JP7634898B2 - Display device - Google Patents

Description

The present invention relates to a display device that makes it difficult to recognize the boundary between the inside and outside of the screen of a display means arranged behind a mask means.

In recent years, with the spread of car navigation systems (so-called car navigation systems) and the development of car audio, there has been an increase in the number of cases where display devices (hereinafter referred to as in-vehicle monitors) are installed inside automobiles. Also, an increasing number of automobiles are equipped with a camera (hereinafter referred to as a backup camera) at the rear of the automobile, and an image of the rear view is displayed on the in-vehicle monitor when the vehicle is reversing. Meanwhile, the installation forms of in-vehicle monitors are also diversifying, and include those that are fixedly installed on the dashboard, those that are built into the dashboard, those that are built into the headrest of the driver's seat or passenger seat for use in the back seat, and those that incorporate a liquid crystal display device into the rearview mirror for rear visibility. Hereinafter, a liquid crystal display device incorporated into a rearview mirror will be referred to as a rearview mirror monitor.

The rearview mirror monitor is equipped with a liquid crystal display device on the rear of the rearview mirror, and the portion of the mirror that corresponds to the screen area of the liquid crystal display device is made into a half mirror, so that the image displayed on the liquid crystal display device can be viewed through the mirror surface. In other words, when an image is displayed on the above-mentioned liquid crystal display device, the light from the screen passes through the half mirror area, so the user can view the displayed image.

In contrast, when nothing is displayed on the liquid crystal display device, no light passes through the half mirror area, and the half mirror area mainly reflects external light. For this reason, the half mirror area functions as a mirror, and when nothing is displayed on the liquid crystal display device, the rearview mirror monitor appears at first glance to be no different from an ordinary rearview mirror. Therefore, the part of the rearview mirror in which the half mirror area is formed can be said to be a masking means that makes it difficult to see the boundary between the inside and outside of the screen of the liquid crystal display device.

Patent Document 1 also proposes a conventional structure for a backlight for a liquid crystal display device, in which a resin composition that performs the optical functions of diffusing, concentrating, and refracting transmitted light in a certain direction is formed on the upper surface of a transparent base layer, while a bright line prevention layer is formed on the lower surface of the base layer by performing gradation printing with various inks in the bright line generation zone, such as the outer edge on the lamp side. This bright line prevention layer is composed of a solid area and a gradation area, and this gradation area makes it possible to blur the boundary line of the bright line prevention layer and makes the bright line prevention layer difficult to see on the LCD screen.

Patent document 2 also proposes that in an image display device capable of displaying an image signal with an aspect ratio different from that of the display screen, the blank area around the image area, which is added when converting the image signal to match the aspect ratio of the display screen, be displayed in a gradation to provide a more creative display.

Furthermore, Patent Document 3 proposes a television receiver that, when displaying HD content with an aspect ratio of 16:9 that includes SD content with an aspect ratio of 4:3, performs gradation processing to gradually change the brightness of the band image so that the difference with the brightness of the SD image falls within a specified range in order to avoid screen burn-in at the boundaries between the SD content display area and the band areas on both the left and right sides.

JP 2002-214407 A JP 2007-150502 A JP 2008-300930 A

As described above, in conventional rearview mirror monitors, when no image is displayed on the liquid crystal display device, the screen of the liquid crystal display device is made difficult to see from the outside by the masking means, making it difficult to distinguish from an ordinary rearview mirror. However, when an image from a car navigation system or a backup camera is displayed on the screen of the liquid crystal display device, the displayed image may cause the edges of the screen to become apparent. In such cases, the viewer is made aware of the screen area of the liquid crystal display device, and as a result, the image seen through the rearview mirror is obviously given the impression that it is displayed by a liquid crystal display device that has been retrofitted to the rearview mirror, which may be disappointing to the viewer.

The present invention was made in consideration of the above problems, and aims to provide a display device that can display an image in such a way that the screen area of the display device installed behind the masking means is not made noticeable, giving the impression that the entire area of the masking means is the screen of the display device.

In order to solve the above problems, the present invention provides the following.
(1) a display means for displaying an image on a screen;
A display device comprising: a mask means arranged in front of the screen, the mask means making it difficult to visually recognize a boundary between inside and outside the screen when no image is displayed on the screen;
The display device is characterized in that the display means performs display such that when an image is displayed on the screen, the boundary between inside and outside the screen is difficult to recognize.

The "display means" here may be anything that displays an image, such as a CRT, a liquid crystal display, an organic EL display, or a plasma display. The "mask means" may be, for example, a half-mirror area in the rear-mirror portion of a rear-mirror monitor, or an area consisting of a mirror area and a half-mirror area, or a transparent member with reduced light transmittance such as smoked glass.

According to the invention of (1) described above, when an image is displayed on a screen, the "display means" performs display that makes it difficult to recognize the boundary between inside and outside the screen, so that the screen area of the "display means" installed behind the "mask means" can be made hard to perceive not only when no image is displayed on the screen as in the past, but also when an image is displayed on the screen. In other words, the screen area can always be made hard to perceive. This gives the viewer of the image the impression that the entire area of the mask means is the screen of the display device. It also gives the impression that the entire area of the mask means is the screen of the display device at all times.

In particular, the masking means is preferably configured to make the boundary between the inside and outside of the screen of the display means less visible over the entire area of the boundary. For example, if the screen of the display means is a rectangular screen, the masking means is preferably configured to make the boundary less visible over the entire area of the four sides.
The masking means may be configured to make the boundary between inside and outside the screen less visible over the entire area of the boundary, and may further have a predetermined area extending from the boundary to the outside of the screen.
Furthermore, the masking means may have these configurations as well as a configuration having an area covering the entire screen.

(2) The display device described in (1) above, characterized in that the display means performs display that makes it difficult for subjective contours to appear that are recognized as boundaries between inside and outside the screen.

Here, the term "subjective contour" refers to a contour that is subjectively recognized by the viewer, even though it does not physically exist. For example, it refers to an optical illusion in which a contour is perceived even though there is no change in brightness or color along the contour.

According to the invention of (2) described above, a display is provided that makes it difficult to produce a subjective contour that is recognized as a boundary between inside and outside the screen, thereby reducing the possibility of creating an optical illusion that a boundary between inside and outside the screen exists in a position where such a boundary does not actually exist. The display that makes it difficult to produce a subjective contour that is recognized as a boundary between inside and outside the screen can be configured in the same way as the "display that makes the boundary difficult to recognize" described in (3) and subsequent items, and a configuration having the components of (7) is particularly effective, with a configuration having the components of (8) being the most effective.

(3) The display device according to (1) or (2) above, characterized in that the display means displays the image on the screen in a gradation manner, gradually decreasing the brightness in the direction outside the screen, to make the boundary less recognizable.

Here, the gradation display may start uniformly from a point a fixed distance away from the screen boundary, or the starting point of the gradation display (distance from the screen boundary) may be changed depending on the display color of the image displayed on the screen. For example, for colors that are easily detected by the human eye, the gradation display may start from a point farther away from the screen boundary, and for colors that are less easily detected by the human eye, the gradation display may start from a point closer to the screen boundary.

According to the invention of (3) described above, the information displayed on the screen is displayed so that the brightness gradually decreases toward the outside of the screen, so that it is possible to approach a state in which no image is displayed at the boundary between the inside and outside of the screen. As a result, even when an image is displayed on the screen of the display device, the "mask means" makes it difficult to recognize the boundary between the inside and outside of the screen, and it is possible to give the impression that the entire area of the "mask means" is the screen of the display device.

(4) the screen of the display means is configured as a dot matrix display;
The display device described in (3) above, wherein the display means reduces the brightness of at least some of the dots constituting the screen in the peripheral portion of the screen where the image is displayed, as a display that makes the boundary difficult to recognize.

According to the invention of (4) described above, when an image is displayed on the screen, the brightness near the border of the screen is reduced, so that the border between the inside and outside of the screen can be made to approach a state where no display is present. As a result, even when an image is displayed on the screen of the display device, the "mask means" can make the border between the inside and outside of the screen difficult to recognize, giving the impression that the entire area of the "mask means" is the screen of the display device.

(5) The display device described in (4) above, characterized in that the display means has a brightness adjustment means for adjusting the brightness of the image displayed on the screen in the peripheral portion of the screen.

According to the invention of (5) described above, the "brightness adjustment means" adjusts the brightness of the image displayed on the periphery of the screen, so that the "masking means" can make the boundary between the inside and outside of the screen difficult to perceive, even when an image is displayed on the screen of the display device. In addition, because the brightness can be adjusted, it is possible to make appropriate adjustments to make the boundary between the inside and outside of the screen difficult to perceive.

(6) The display device described in (5) above, wherein the brightness adjustment means, when displaying the peripheral portion of the screen based on image data representing the content to be displayed on the screen, displays the brightness of the display of the peripheral portion of the screen at a lower brightness than the brightness indicated by the image data.

Here, "image data" refers to anything that indicates the content to be displayed on a screen. For example, in addition to image data that shows photographs or figures, "image data" also includes text data that shows the characters to be displayed and their attribute data (such as the color, size, and font of the characters).

A specific embodiment of the brightness adjustment means may be, for example, a configuration in which the brightness of the display at the periphery of the screen is reduced by software processing when performing display control based on "image data." This allows the "masking means" to make it difficult to distinguish the boundary between the inside and outside of the screen without making any changes to the hardware configuration, so it is possible to keep costs down while still giving the impression that the entire area of the "masking means" is the screen of the display device.

(7) The display device described in (6) above, characterized in that the brightness adjustment means changes the position of the dot at which the gradation display begins or the gradient of the gradation when the gradation display is performed.

According to the invention of (7) described above, the width of the gradation area added to the displayed image or the slope of the brightness change in the image displayed within the gradation area is not uniform, making it difficult to create a subjective contour that is recognized as the boundary between the inside and outside of the screen.

(8) The display device described in (7) above, wherein the brightness adjustment means changes the position of the dot at which the gradation display starts or the gradient of the gradation when the gradation display is performed at a predetermined timing.

According to the invention of (8) described above, the width of the gradation area added to the displayed image, or the slope of the brightness change in the image displayed within the gradation area, changes at a predetermined timing, making it less likely that a subjective contour that is recognized as a boundary between the inside and outside of the screen will occur.

(9) The display means is
a storage means having a storage area corresponding to each dot of the dot matrix display;
a display data writing means for writing display data relating to display at a corresponding dot into each storage area of the storage means based on the image data;
an image display means for displaying an image on the dot matrix display based on the display data written in each memory area of the memory means;
The display device according to any one of (6) to (8) above, wherein the data writing means writes display data to memory areas among the memory areas corresponding to dots on the periphery of the screen, such that the display of the dots will be at a brightness lower than the brightness specified by the image data.

According to the invention of (9) described above, when performing image display control based on image data, the brightness of the image displayed on the periphery of the screen can be reduced simply by changing the writing process of the display data for each dot based on the image data. This makes it difficult to distinguish the boundary between the inside and outside of the screen by the "masking means" without making any changes to the hardware configuration, so it is possible to keep costs down while giving the impression that the entire area of the "masking means" is the screen of the display device.

(10) The display device described in (9) above, characterized in that when the data writing means writes the display data to each memory area of the storage means in order to display an object on the screen based on the image data, the data writing means changes the display data to one in which the peripheral portion of the object is displayed with a gradation.

According to the invention of (10) described above, not only is the brightness of the peripheral parts of the screen reduced, but the peripheral parts of the image representing the object are also displayed with a gradation. As a result, for example, if the shape of the displayed object is a polygon made up of straight lines, one of whose sides is a straight line parallel to the boundary between the inside and outside of the screen, the side forming the outline of the object may appear to be the boundary between the inside and outside of the screen. Therefore, in order to avoid such misconception, the peripheral parts of the object are also displayed with a gradation, thereby reducing the possibility of the user being aware of the screen area of the display device, and giving the impression that the entire area of the masking means is the screen of the display device.

(11) The data writing means
determining whether the object to be displayed within the screen is entirely displayed;
The display device described in (9) above is characterized in that when it is determined that a portion of the display of the object is not displayed within the screen, display data is written to a memory area corresponding to the dot in the peripheral part of the screen for the object displayed within the screen, such that the display of the dot has a brightness lower than the brightness specified by the image data.

According to the invention of (11) described above, when the entire image of the object to be displayed does not fit within the screen and part of the object is cut off at the edge of the screen, the display of the object at the edge of the screen is displayed in a gradation. This makes it possible to reduce the possibility that a viewer of the object becomes aware of the screen area of the display device due to part of the object being cut off at the edge of the screen.

(12) The data writing means comprises:
In the screen,
The display device according to (9) above, characterized in that when there are a plurality of objects that are not entirely displayed, the gradation display in the peripheral portion of the screen for each of these objects is made different from one another.

According to the invention of (12) described above, when there are multiple objects in the image to be displayed that are displayed all the way to the edge of the screen, the gradation display of the peripheral portion of the screen is different for each of these objects, so that the edges of each object do not align linearly along the edge of the screen, making it difficult to create a subjective contour that is recognized as a boundary between inside and outside the screen.

(13) The display device described in (4) above, characterized in that the display means is provided with a transmittance reduction means for reducing light transmittance on the front side and peripheral portion of the screen.

According to the invention of (13) mentioned above, by providing a "transmittance reducing means" around the periphery of the screen, the brightness of the image displayed near the boundary of the screen is reduced, so that the "masking means" makes it difficult to recognize the boundary between the inside and outside of the screen even when an image is displayed on the screen of the display device. Therefore, by adding a simple configuration, it is possible to give the impression that the entire area of the "masking means" is the screen of the display device.

(14) The display means includes an illumination means for illuminating the screen from the rear side to make the image displayed on the screen visible;
The display device according to (4) above, further comprising: a dimming means provided on the rear side and peripheral portion of the screen for dimming the light from the illumination means.

According to the invention of (14) described above, the light from the "illumination means" that illuminates the back side of the screen of the "display means" is dimmed by the "dimming means" for the peripheral parts of the screen, so that even when an image is displayed on the screen of the display device, the "masking means" makes it difficult to recognize the boundary between the inside and outside of the screen. Therefore, with a simple configuration, it is possible to give the impression that the entire area of the "masking means" is the screen of the display device.

(15) The display means includes an illumination means for illuminating the screen from the rear side to make the image displayed on the screen visible,
The display device described in (4) above, wherein the illumination means has a central illumination section that illuminates the center of the screen and a peripheral illumination section that illuminates the peripheral portion, and the amount of light of the peripheral illumination section is less than the amount of light of the central illumination section.

According to the invention of (15) above, the lighting that illuminates the back side of the screen is darker at the periphery of the screen than at the center of the screen, so that the "masking means" makes it difficult to distinguish the boundary between the inside and outside of the screen even when it is displayed on the screen of the display device. Therefore, it is possible to give the impression that the entire area of the "masking means" is the screen of the display device without using any additional means other than the "lighting means".

As described above, according to the present invention, by performing a display that does not draw attention to the screen area of the display device installed behind the masking means, it is possible to give the impression that the entire area of the masking means is the screen of the display device.

1A and 1B are diagrams showing the appearance of a radar detector equipped with a display device according to an embodiment of the present invention, where FIG. 1A is a front view and FIG. FIG. 2 is a functional block diagram of the radar detector and its remote control. 1A and 1B are explanatory diagrams for explaining the contents of images displayed on the display device of the radar detector, in which (a) shows an image on the standby screen, and (b) shows the contents of an image on the radar scope screen. 2 is an explanatory diagram for explaining a display mode of an image displayed on the display device. FIG. 11 is an explanatory diagram for explaining the contents of gradation data for adding gradation to an image displayed on the display device. FIG. 11 is an explanatory diagram for explaining a case where a gradation is added to an object displayed on the display device. FIG. 13 is an explanatory diagram for explaining a case where different gradations are added to a plurality of objects having different display colors in a map image displayed on the display device. FIG. 13 is an explanatory diagram for explaining a structure for adding a gradation area to an image to be displayed in the display device. FIG. 13 is an explanatory diagram for explaining the structure of an illumination means for adding a gradation area to a displayed image in the display device. FIG.

The display device according to the embodiment of the present invention will be described below with reference to the drawings. In the embodiment described below, the overall configuration of the display device will first be described.

<Overall configuration of a radar detector>
1(a) and (b) show the external appearance of a radar detector equipped with an embodiment of a display device of the present invention. The radar detector 10 is equipped with various mechanisms shown in Fig. 2 inside and outside a rectangular parallelepiped housing 11 that forms the main body, and the radar detector 10 is fixed in place by clamping a rearview mirror (not shown) installed inside the vehicle from above and below with fasteners 12a and 12b provided on the back of the housing 11.

As shown in FIG. 1(a), the front of the housing 11 (the surface facing the driver) is provided with a rectangular mirror member 13, which is a mirror for reflecting the rear of the vehicle, and the right rear of the mirror member 13 is provided with a display unit 14 (hereinafter, also referred to as "screen 14" depending on the explanation). In this embodiment, a small 2.8-inch liquid crystal display is used as the display unit 14. In the mirror surface of the mirror member 13, the area facing the screen of the display unit 14 (area HM shown by the dashed line in FIG. 1(a)) is a half mirror. In the following, the area shown by the dashed line in FIG. 1(a) is referred to as the half mirror area HM. Also, the area other than the half mirror area HM is referred to as the mirror area M. The area consisting of the half mirror area HM and the mirror area M corresponds to a masking means, and as a result, when some image is displayed on the screen of the display unit 14, the image can be viewed through the half mirror area HM. Furthermore, when the display unit 14 is not displaying any image (when the screen is completely black), the surrounding scenery is reflected in the half mirror area HM, making it extremely difficult to see the screen of the display unit 14 located behind it. An infrared receiving unit 15 for receiving infrared signals from a remote control 28 (see Figure 2) is provided above the half mirror area HM.

As shown in FIG. 1(b), a sound emission hole 18 is formed on the right side of the rear surface of the housing 11 (the surface facing the front window) in the figure, which allows sound output from a speaker 17 as a sound output means to pass to the outside. In addition, an insertion hole 19 for a DC power jack is formed on the rear surface of the housing 11 at approximately the upper center in the figure. Although not shown, in this embodiment, the power supply for the main body side of the radar detection device 10 is obtained from the cigarette lighter socket (i.e., the secondary battery, which is the battery of the vehicle) via a cigarette plug cord that electrically connects the DC jack to the cigarette lighter socket of the vehicle. Furthermore, a microwave receiver 22 and a wireless receiver 23 are built in below the insertion hole 19, and a GPS receiver 21 is built in to the right of the microwave receiver 22 and the wireless receiver 23.

The left side of the housing 11 shown in FIG. 1(b) is formed with a slot 20 for inserting a memory card 25 as a storage medium into a memory card reader 24 (see FIG. 2 for both). The memory card reader 24 can import data stored in the memory card 25, and write the contents of the database 27 and memory of the control unit 26 shown in FIG. 2 to the memory card 25. More specifically, if the data stored in the memory card 25 contains updated information about new alarm target information (location information including longitude and latitude, type information, etc.), the control unit 26 stores (downloads) the updated information in the database 27 built into the device, and updates the data in the database 27.

In FIG. 2, database 27 is a non-volatile memory (e.g., EEPROM) inside the microcomputer that is control unit 26 or externally attached to the microcomputer. Information about certain alarm targets is registered in database 27 at the time of shipment, and information about new alarm targets that are added later can be updated in the manner described above.

The wireless receiver 23 receives wireless signals of a specific frequency. The infrared receiver 15 communicates data with a remote control (portable device: child device) 28 via infrared rays, and performs various settings for the device. The remote control 28 is equipped with a standby switch button, a first setting button, a second setting button, a selection button, a cancel button, a decision button, and up, down, left and right cross buttons (all not shown).

The control unit 26 is a microcomputer equipped with a CPU 260, ROM 262, RAM 264, VRAM 266, I/O, etc. (not shown), and executes predetermined processing based on information input from the various input devices mentioned above, and outputs predetermined warnings, messages, and information using output devices. Note that the VRAM 266 has memory areas that correspond to each pixel that constitutes the screen of the display unit 14. These basic configurations can basically be the same as those of conventional devices.

The functions of the radar detector 10 of this embodiment are stored as programs in the EEPROM of the control unit 26, and are realized by the CPU of the control unit 26 executing these programs. Functions executed by the CPU through programs include a GPS log function, a standby screen display function, a radar scope display function, a GPS warning function, a radar wave warning function, and a wireless warning function, and the warning means of the present invention is embodied as one function of the CPU of the control unit 26.

The GPS log function is a function in which the control unit 26 associates the current position detected by the GPS receiver 21 every second with the detection time and speed (vehicle speed) and stores the position history in non-volatile memory. This position history is recorded, for example, in the NMEA (National Marine Electronics Association) format.

The standby screen display function is a function that displays the vehicle's speed 141, latitude 142, and longitude 143 detected by the GPS receiver 21 on the display unit 14, as shown in FIG. 3(a).

When the standby screen display function, GPS warning function, radar wave warning function, or wireless warning function is being executed, the screen display area 140 of the display unit 14 is divided into a main display area 140A and an icon display area 140B, and information related to each function is displayed exclusively in the main display area 140A. On the other hand, a compass icon 144, a road selection icon 145, a radar reception sensitivity mode icon 146, and a mode selection icon 147 are displayed in the icon display area 140B. Furthermore, the current time 148 is displayed at the right end of the icon display area 140B.

The radar scope display function, as shown in FIG. 3(b), searches for alarm targets within a predetermined range (for example, within about 1 km) from the current position detected by the GPS receiver 21 based on the position information stored in the database 27, and displays the relative positional relationship between the vehicle and the alarm targets on the display unit 14.
Note that the diagrams shown in Figures 3(a) and (b) are both intended to explain the contents that are displayed while each function is being executed, and the specific manner in which these contents are displayed will be explained in detail later.

When the radarscope display function is being executed, a map 151 based on the map information stored in the database 27 is displayed in the main display area 140A, and an arrow-shaped vehicle icon 152 indicating the vehicle's position is displayed on this map 151. Furthermore, if an event occurs while the radarscope display function is being executed (if a predetermined condition for issuing an alarm is met), an alarm target icon 153 having letters such as "L", "RD", "P", "N", etc. is displayed on the map 151 to indicate the type and position of the alarm target. Furthermore, when the radarscope display function is being executed, the legal speed limit 154 of the road the vehicle is traveling on and the vehicle's current speed 155 are displayed in the lower right corner of the main display area 140A.

When the control unit 26 detects that the standby switch button on the remote control 17 is pressed while the standby screen display function shown in Fig. 3(a) is being executed, the control unit 26 switches to the radarscope display function shown in Fig. 3(b). Also, when the control unit 26 detects that the standby switch button on the remote control 17 is pressed while the radarscope display function is being executed, the control unit 26 performs processing to switch to the standby screen display function.

When an event occurs while the standby screen display function or the radar scope display function (hereinafter, these functions are collectively referred to as the standby functions) is being executed, the control unit 26 executes processing to realize each of the GPS warning function, the radar wave warning function, and the wireless warning function. The priority of each function is set in the order of highest to lowest: radar wave warning function, wireless warning function, and GPS warning function.

The GPS warning function is a process executed at a predetermined time interval (1 second intervals) in response to an event from a timer in the control unit 26. It calculates the distance between the object of warning stored in the database 27 and the current latitude and longitude of the vehicle detected by the GPS receiver 21, and when the calculated distance becomes a predetermined approach distance (for example, within 2 km), it displays a warning on the display unit 14 and outputs a warning sound such as sound effects, background music, or voice from the speaker 17.

Targets that the GPS warning function may warn of include, for example, speed measuring devices (loop coils, LH systems, H systems, radar speed cameras, etc.), speed trap areas, mobile speed cameras areas, tracking enforcement areas, stop enforcement areas, intersection enforcement areas, other enforcement areas, seat belt checkpoints, drunk driving checkpoints, cell phone checkpoints, other checkpoints, intersection monitoring points, signal ignoring prevention systems, highway traffic police, N systems, traffic monitoring systems, police stations, accident-prone areas, service areas, parking areas, highway oases, long/continuous highway tunnels, highway radio receiving areas, roadside stations, view point parking, parking lots, public toilets, etc., and information on the type of target to be warned, latitude and longitude information indicating its location, schematic or photographic data to be displayed on the display unit 14, and audio data are stored in the database 27 in association with each other.

The radar wave warning function is a warning function that displays a warning on the display unit 14 and outputs a warning sound from the speaker 17 when the microwave receiver 22 detects radio waves equivalent to microwaves of a specific frequency band emitted by a speed measuring device. For example, when microwaves of a specific frequency band emitted by a speed measuring device are detected by the microwave receiver 22, a schematic diagram or photo of a radar stored in the database 27 is displayed as a warning on the display unit 14, and audio data stored in the database 27 is read out and a voice saying "This is radar. Watch your speed" is output from the speaker 17.

The radio warning function is a function that issues a warning when radio waves emitted by an emergency vehicle or the like are received by the radio receiver 23 so as not to interfere with the driving of the vehicle. The radio warning function scans the frequencies of police radio, car location radio, digital radio, special small radio, police station radio, police telephone, police activity radio, tow truck radio, helicopter radio, fire helicopter radio, fire radio, emergency radio, highway radio, security radio, etc., and when a radio signal is received at a scanned frequency, a schematic diagram indicating that a radio signal corresponding to the frequency stored in the database 27 for each radio type is received is displayed on the display unit 14 as a warning screen, and audio data stored in the database 27 for each radio type is read out and an alarm sound indicating the type of radio signal is output from the speaker 17. For example, when a police radio signal is received, a sound such as "This is a police radio. Watch your speed" is output.

Here, as described above, the radarscope display function, GPS warning function, radar wave warning function, and wireless warning function are set with multiple different types of warning targets, and a priority order is set according to the type of warning target. The priority order of each warning target is visualized, for example, by color-coding the warning target icon 153 shown in FIG. 3(b) into groups of "red," "yellow," "blue," or "green" in order of decreasing priority. For example, for warning targets belonging to the "red" group with the highest priority, a warning is issued in the characteristic display mode of this embodiment described below, and for warning targets belonging to the "yellow," "blue," or "green" groups with the second or lower priority, a warning is issued in the same general display mode (not shown) as in the past.

<Display mode of image on the screen of the display device>
Next, the display mode of the image displayed on the screen of the display device in this embodiment will be described with reference to Fig. 4. The display mode shown in Fig. 4 is obtained by applying the display mode of the display device in this embodiment to the image displayed during execution of the radarscope display function shown in Fig. 3(b). Moreover, the display mode shown in Fig. 4 illustrates the mode displayed on the screen of the display unit 14, and does not illustrate the display mode visually recognized through the half mirror region HM of the mirror member 13.

As shown in FIG. 4, the image displayed on the display device of this embodiment has a gradation area G of a constant width W that gradually becomes brighter from the outermost edge (hereinafter also referred to as the edge) of the screen of the display unit 14 toward the inside of the screen, and the original brightness of the displayed image is reached when the boundary of the gradation area G, shown by the dashed line in the figure, is reached. In other words, within the gradation area G, the image becomes darker as it moves from the boundary toward the outside (the edge of the screen), and by the time it reaches the outermost edge of the screen of the display unit 14, it is completely black with nothing displayed. This gradation area G corresponds to the "peripheral part of the display area." In addition, hereinafter, the area of the screen of the display unit 14 that is not the gradation area G (the area within the dashed line in FIG. 4) is referred to as the normal area N.

It goes without saying that the dashed lines indicating the boundaries of the gradation area G in FIG. 4 are not displayed on the screen of the display unit 14. Furthermore, the shape and position of the gradation area G are constant, and even if the display of the vehicle icon 152 moves or the display of the map 151 scrolls as a result of the vehicle equipped with the radar detector 10 traveling, for example, the gradation area G does not move or deform accordingly.

The width of the gradation area G refers to the length in the vertical direction relative to the edge of the screen. The width of the gradation area G and the degree of change in brightness in the direction of width W (hereinafter also referred to as the brightness gradient) can be determined appropriately depending on the size of the half-mirror area HM in the mirror member 13 relative to the size of the screen of the display unit 14, the light transmittance of the half-mirror area HM, and the specifications related to the image display of the display unit 14. In other words, the gradation area G can be determined so that when an image displayed across the entire screen of the display unit 14 is viewed through the half-mirror area HM of the mirror unit 13, the edges of the screen are difficult to see.

(Action and Effects)
In this way, by adding the gradation area G as shown in FIG. 4 to the image to be displayed, the following effects are achieved.
First, in the front view of the radar detector 10 shown in FIG. 1(a), when no image is displayed on the screen of the display unit 14, it is difficult to distinguish between the half mirror area HM and the mirror area M, and the front of the mirror member 13 looks like a uniform mirror. For this reason, the boundary between the inside and outside of the screen of the display unit 14 is difficult to see. In this state, for example, assume that an image is displayed on the screen of the display unit 14 in which the image portion to be displayed is bright and the other background portions are dark. When this image is viewed through the half mirror area HM of the mirror member 13, the image to be displayed can be clearly seen, but the background portion looks like a mirror because the light transmitted through the half mirror area HM (except for the image portion to be displayed) is weak and the reflected light is dominant. As a result, in the mirror member 13, it looks as if only the image to be displayed is floating in the mirror.

In contrast to this, when a bright image is displayed across the entire screen of display unit 14 as in the conventional case, there are areas where the difference between light and dark is noticeable inside and outside the edges of the screen of display unit 14, and when such an image is viewed through the half-mirror area HM, the shape of the screen of display unit 14 (usually rectangular) becomes clearly noticeable.
Also, for example, if a road is drawn up to the edge of the screen of the display unit 14, a viewer will feel as if the display is cut off because the road extending outside the screen has reached the edge of the screen. In this way, if an image that reaches the edge of the screen and has a portion that continues outside the screen (for example, an image in which only a portion of an object having a predetermined shape as a whole is displayed) is cut off at the edge of the screen, the shape of the screen of the display unit 14 will be brought into focus.
This makes the viewer aware that he or she is not looking at an image reflected in the mirror of the mirror member 13, but is simply looking at the screen of the display unit 14 provided on the back side of the mirror member 13, which may cause the viewer to lose interest or feel dull.

In this embodiment, a gradation area G of a certain width W is provided from the edge of the screen of the display unit 14, and the image displayed near the edge of the screen of the display unit 14 gradually transitions from "light" to "dark" as it moves toward the edge of the screen, making the edges of the screen of the display unit 14 less noticeable when the image is viewed through the half mirror area HM. This has the effect of making it difficult to be aware of the shape of the screen of the display unit 14 at all times, whether an image is being displayed on the screen of the display unit 14 or not, reducing the likelihood that the person viewing the displayed image will feel disappointed or dull.

<Embodiments for adding gradation areas to an image>
Next, various embodiments for adding the gradation area G shown in FIG. 4 to the image displayed on the display unit 14 will be described.

First Embodiment
First, a first embodiment will be described. In the first embodiment, a gradation area G as shown in Fig. 4 is added by image processing carried out when an image is displayed on the screen of the display unit 14. Hereinafter, this image processing will be referred to as gradation addition processing, and the details thereof will be described below.

First, the CPU 260 determines the display data for one pixel in a predetermined order based on the image data to be displayed, among the image data stored in the database 27 shown in FIG. 2.

Here, the "predetermined order" refers to, for example, assuming that the pixels constituting the screen of the display unit 14 are arranged in a matrix of m rows and n columns, the order is from the pixel in the first column to the pixel in the nth column for each pixel row, starting from the first row, through to the mth row, in that order. That is, the order is from (first row, first column) to (first row, nth column), then from (second row, first column) to (second row, nth column), then from (third row, first column) to (third row, nth column), ... and finally from (mth row, first column) to (mth row, nth column).
Moreover, the "display data" is data that specifies the display color for each pixel, and is, for example, data that indicates the gradation (0 to 255) for each of the three primary colors (RGB).

Next, the CPU 260 refers to the gradation data stored in the ROM 262 shown in FIG. 2, and recognizes the brightness coefficient (hereinafter referred to as the brightness coefficient) that is predetermined for the pixel whose display data has been determined based on the image data. This gradation data specifies the brightness coefficient described above for each pixel that constitutes the screen of the display unit 14. This brightness coefficient takes values ranging from 0 to 1, with "0" meaning that the brightness is "0" (i.e., black), and "1" meaning that the brightness of the determined display data remains the same. Values greater than "0" and less than "1" indicate the percentage by which the brightness is to be reduced relative to the brightness of the determined display data.

The CPU 260 then multiplies the recognized brightness coefficient value by the display data determined above, i.e., the values indicating the gradations for each of the RGB colors, and sets the result as the display data to be used for actual display (hereinafter referred to as converted display data). The converted display data calculated for one pixel is then stored in the memory area corresponding to that pixel in the VRAM 266 (see FIG. 2), and the converted display data for the next pixel is calculated according to the predetermined order described above. Once the converted display data has been calculated for all pixels constituting the screen of the display unit 14 in this manner, the CPU 260 displays an image by driving each pixel constituting the screen of the display unit 14 according to the converted display data stored in the VRAM 266.

Next, the contents of the gradation data stored in the ROM 262 described above will be explained. As described above, the gradation data is composed of a brightness coefficient for each pixel that constitutes the screen of the display unit 14. For example, in the screen shown in FIG. 4, the brightness coefficient value is "1" for pixels included in the normal area N. In addition, the brightness coefficient value is "0" for pixels at the outermost edge of the screen of the display unit 14 (i.e., the pixels in the first to nth columns in the first and mth rows, and the pixels in the first to mth rows in the first and nth columns). Furthermore, the brightness coefficient value for pixels from the boundary B (shown by a dashed line in FIG. 4) between the normal area N and the gradation area G to the outermost edge of the screen gradually decreases from "1" to approach "0". Here, the slope of the change in the brightness coefficient value from "1" to "0" may be a straight line or a curve.

Here, if the width W of the gradation area G is constant and the gradient of the brightness coefficient value for each pixel within the gradation area G in the gradation data is uniform, the subjective contour is easily recognized due to human cognitive characteristics. Here, the "subjective contour" refers to an optical illusion in which a contour is perceived even though there is no change in brightness or color along the contour. Note that the "subjective contour" of concern in this embodiment is a non-existent edge of the screen that is perceived by the viewer of the image due to changes in brightness or color of the image viewed through the half-mirror area of the mirror member 13. Therefore, hereinafter, when the term "subjective contour" is used simply, it means "a non-existent edge of the screen that is perceived by the viewer of the image."

The content of the displayed image may also make the "subjective contour" easier to recognize. For example, in the icon display area 140B shown in FIG. 3, four square icons (compass icon 144, road selection icon 145, radar reception sensitivity mode icon 146, and mode selection icon 147) are displayed in a horizontal row on the left side of the figure, and the current time is displayed on the right side of the figure. When displayed in this manner, there is a possibility that the subjective contour will be recognized by the lines connecting the bottom sides of the four icons to the bottom of each letter and number of the current time.

In addition, in the map 151 of Fig. 6, because the three roads reach the left edge of the screen, it is perceived as if the display of the roads that should continue further is cut off, and this makes it easy to recognize that the edge of the screen is in that area. Moreover, a line connecting the ends of these three roads from a certain direction (for example, from above) is recognized as the subjective contour. Since this line coincides with the left edge of the screen, the edge of the screen is ultimately recognized as the subjective contour as well.
Therefore, by applying a gradation of a certain width w as explained above, it is possible to make the ends of the road less noticeable, and by reducing the feeling that the display of the road is being cut off, it is possible to make the edges of the screen less noticeable.

For example, in order to make the above-mentioned "subjective contour" less noticeable, the gradation data stored in the ROM 262 may be set to the content shown in FIG. 5. That is, to impart a gradation of a certain width w as shown in FIG. 4, the brightness coefficient value for each pixel is set to decrease uniformly from "1" to "0" from the pixel located on the boundary B shown in FIG. 5 toward the pixel located on the edge of the screen. Here, the pixel located on the boundary B is the pixel located on the line connecting the four pixels of the wth row and wth column, the wth row and n-wth column, the m-wth row and wth column, and the m-wth row and n-wth column. That is, the shape of the boundary B is a rectangle (shown by a thin dashed line in FIG. 5), and the brightness coefficient is decreased uniformly from the pixel located on each boundary B toward the pixel located on the edge of the screen. In the following, for example, the pixel located on the wth row and wth column will be written as the pixel (w, w).

However, if the shape of boundary B is similar to the shape of the edge of the screen, there remains the possibility that the edge of the screen will be recognized as a subjective contour. Therefore, in order to make the "subjective contour" less noticeable, the shape of boundary B is deformed so that it is an arbitrary curve, for example, as shown by the thick dashed line B' in FIG. 5, rather than a rectangle, and gradation data is set so that the brightness coefficient value for each pixel decreases from "1" to "0" from the pixel located on boundary B' after the deformation to the pixel located on the edge of the screen. How boundary B is deformed can be determined as appropriate, but for example, using the pixels located on boundary B as a reference, the pixels after moving each pixel a number of pixels in the row or column direction within a predetermined maximum movement width are regarded as pixels located on boundary B'.

For example, as described above, the pixels located on the boundary B are pixels located on the line connecting the four pixels (w,w), (w,n-w), (m-w,w), and (m-w,n-w). For pixels located on the line connecting (w,w) and (w,n-w) and on the line connecting (m-w,w) and (m-w,n-w), the column value is increased or decreased arbitrarily within a predetermined numerical range (for example, ±30). For pixels located on the line connecting (w,w) and (m-w,w) and on the line connecting (w,n-w) and (m-w,n-w), the row value is increased or decreased arbitrarily within a predetermined numerical range (for example, ±30). After the pixels located on the boundary B' are thus determined, the gradation data is set so that the brightness coefficient value for each pixel decreases from "1" to "0" from each of these pixels toward the pixels located on the edge of the screen.

The gradation data as described above may be determined in advance and stored in ROM 262 shown in FIG. 2, or may be generated by CPU 260 based on a function or the like. For example, information that can identify pixels located on the reference boundary B is stored in ROM 262, and CPU 260 determines boundary B' shown in FIG. 5 based on that information. Next, CPU 260 obtains gradation data in which the brightness coefficient value decreases from pixels located on the determined boundary B' toward pixels located on the edge of the screen. The gradation data obtained by this process is then stored in database 27 shown in FIG. 2. As a result, when CPU 260 displays the image shown in FIG. 4, CPU 260 adds a gradation based on the gradation data stored in database 27.

The above-mentioned gradation data arbitrarily changes the width of the gradation area by arbitrarily changing the shape of the boundary B. Alternatively, the gradient of the brightness coefficient value may be arbitrarily changed when decreasing the brightness coefficient value for each pixel from "1" to "0" from each pixel located on the rectangular boundary B toward the pixel located on the edge of the screen. For example, the brightness coefficient value may change linearly from "1" to "0" from the position on the rectangular boundary B to the position on the edge of the screen, the brightness coefficient value may become "0" from the position on the boundary B to a position closer to the boundary B than the edge of the screen, the gradient of the change may be steep, or the brightness coefficient value may change in a curved manner (convex curve or concave curve). In the following, the gradient of the change in the brightness coefficient is referred to as the brightness gradient.

In this way, by changing the brightness gradient in the gradation data, the aspect of the gradation added to the image can be changed arbitrarily, making it difficult for the viewer to recognize the "subjective contour". In this method as well, gradation data with a changed brightness gradient may be stored in ROM 262 in advance, or information that can identify pixels located on boundary B may be stored in ROM 262, and CPU 260 may arbitrarily change the brightness gradient from each pixel to the image located on the edge of the screen based on that information, and store the obtained gradation data in database 27. Furthermore, the above two methods may be combined to first determine a deformed boundary B', and then arbitrarily change the brightness gradient from each pixel located on boundary B' to the pixel located on the edge of the screen.

When the gradation data is determined by the CPU 260, it is even better to update the gradation data at a predetermined timing. Examples of the predetermined timing may be when the radar detector 10 is turned on, when a predetermined number of days have passed, when a predetermined time has passed, when the displayed screen is changed, etc. In this way, it is possible to suppress not only subjective contours that match or are close to the edges of the screen, but also subjective contours that may be caused by the boundary B or gradation pattern.

Furthermore, to make it difficult for viewers to recognize the "subjective contours," it is advisable to eliminate displays that tend to make subjective contours more noticeable as much as possible. For example, as described above, in the icon display area 140B shown in FIG. 3, four square icons are displayed in a horizontal row on the left side of the figure, and the current time is displayed on the right side of the figure, so that the subjective contours are easily recognized by the lines connecting the bottom sides of each icon to the bottom of the letters and numbers that represent the current time.

Therefore, in order to prevent the four icons and the current time from being aligned in a straight line, the display positions of each icon in the vertical direction in the figure may be shifted appropriately, or the shape of the icons may be changed so that the outline of each icon is not parallel to the edge of the screen. Possible icon shapes that make it difficult to recognize the subjective outline include, for example, icons whose outline is made up of diagonal straight or curved lines so that the outline of the icon is not parallel to the edge of the screen, or icons that omit the outline. Also, when text is displayed, the text may be displayed in color, but it is recommended that the entire area around the text be black.

In this way, the control unit 26, which performs the above-mentioned gradation addition process when displaying an image, can be said to correspond to the "brightness adjustment means." In addition, the above-mentioned VRAM corresponds to the "storage means," and the control unit 26 can also be said to correspond to the "data writing means" and "image display means."

(Modification of the first embodiment)
As a method of adding the gradation area G, instead of writing display data that is darker than the actual brightness based on the image data and written to the storage area corresponding to each pixel of the VRAM as described above, the number of pixels for displaying the image may be gradually reduced. That is, instead of writing the display data that would normally be used to display the map 151 to the storage area corresponding to each pixel of the VRAM, display data that is the same as the background image (e.g., black) is written, and the number of such pixels is gradually increased from the boundary between the normal area N and the gradation area G toward the periphery of the screen.

Specifically, as the aforementioned gradation data, for pixels included in gradation area G, data indicating that fact is defined, as well as data indicating whether to use the display data determined in step S10 of FIG. 5 or to use the same display data as the background image (hereinafter referred to as conversion specification data). Then, as a result of the determination process in step S12 of FIG. 5, when CPU 260 performs the process of step S14, it stores the display data determined in step S10 of FIG. 5 or the same display data as the background image in the corresponding storage area of the VRAM according to the conversion specification data corresponding to that pixel.

Therefore, in the gradation data of this modified example, the closer one gets to the edge of the screen, the greater the proportion of pixels within a certain area that display the same as the background image, and as a result, a gradation area G as shown in Figure 4 is added.
As with the gradation data that specifies the brightness coefficient, the proportion of pixels that display the same as the background image using the conversion specification data described above can be changed so that the boundary between the normal area N and the gradation area G becomes boundary B' shown in Figure 5, or so that the change in the proportion of pixels that display the same as the background image does not become uniform as one approaches the edge of the screen, thereby making it difficult to perceive subjective contours.

(Application example 1 of the first embodiment)
As described above, in this embodiment, the display data for each pixel in the gradation area G is converted to display data that is darker than the original brightness depending on the position of each pixel. Therefore, by changing the pixels that are the subject of the above-mentioned display data conversion, the gradation area on the screen of the display unit 14 can be changed.

For example, when the map 151 and the vehicle icon 152 shown in FIG. 3B are displayed three-dimensionally (3D display), the display position of the horizon H parallel to the long side of the screen is fixed as shown in FIG. 6A, and the background image (area corresponding to the sky) BG of the area above the horizon H in the figure is displayed uniformly darker than the display of the map 151. If the gradation area G shown in FIG. 4 is added to such an image, the brightness gradient in the gradation area G is reflected in the image of the map 151 near the left and right sides and the bottom side of the screen, but the brightness gradient in the gradation area G is not reflected in the image of the map 151 near the horizon H. For this reason, the contrast between the image of the map 151 and the background image BG becomes noticeable with the horizon H as the boundary, and when such an image is viewed through the half mirror area HM of the mirror member 13, the horizon H of the map 151 is clearly visible and may be recognized as if it were the edge of the screen.

Therefore, in this embodiment or its modified example, the display data can be converted so that, in addition to the gradation areas of constant width W from the left and right sides and bottom side of the screen, a gradation area of constant width W is added to the gradation area on the top side from the horizon H downward, as in the gradation area G' shown in FIG. 6(b). In this way, by converting the display data so that a gradation area is added to an area that is not actually an edge of the screen but may be perceived as if it were an edge of the screen depending on the content of the image to be displayed, it is possible to prevent the screen area of the display unit 14 from being perceived as being based on a mistake.

To add the gradation as described above, first, gradation data for adding the gradation area G shown in FIG. 4 and gradation data for adding the gradation area G' shown in FIG. 6(b) are stored in advance in the ROM 262 in FIG. 2. Then, when a map 151 or the like is to be displayed in 3D, the processes in steps S12 to S16 in FIG. 5 are performed based on the latter gradation data.

(Application Example 2 of the First Embodiment)
In the above-mentioned application example 1, the position or range of the gradation area G on the screen is changed according to the image to be displayed. In contrast, in application example 2, the width of the gradation area is changed for each object (hereinafter, referred to as an object) to be displayed as an image.

Figure 7(a) shows an example of the display mode of an image in application example 2. The image shown in this figure is basically the same as the image shown in Figure 4, but in order to more clearly illustrate the features of application example 2, the icon display area 140B is not shown. Also, in this figure, the same parts as those shown in Figure 4 are given the same reference numerals and detailed explanations are omitted. Note that in Figure 6, the roads in the map 151, various icons (own vehicle icon 152, warning target icon 153), legal speed limit 154 and current speed 155, as well as other numbers, letters, lines, etc., displayed as images, are treated as individual objects.

In application example 2, for objects that cannot be displayed entirely within the screen and are partially cut off by the edge of the screen, a gradation area is added to the object from the cutoff point. For example, in the object "road" displayed on the map 151 shown in FIG. 7(a), the roads that reach the edge of the screen are as follows: a wide road R1 that extends vertically in the approximate center of the screen, a wide road R2 that extends horizontally from the left side of the screen to the right and meets road R1, a narrow road R3 that branches off from road R2, a narrow road R4 that extends horizontally from the left side of the screen to the right and intersects with road R1 slightly above road R2, a narrow road R5 that extends diagonally upwards from the upper left side of the screen to the right, intersects with road R4, merges with road R1, and continues to the top of the screen, and a narrow road R6 that extends diagonally upwards to the left and intersects with road R5 at the approximate upper center of the screen.

At the ends of the above-mentioned roads R1 to R6, gradation areas with random widths w1 to w5, w5', and w6 are added from the edge of the screen. As a result, for example, on the left side of the screen shown in FIG. 7(a), the widths w4, w5, w2, and w3 of the gradation areas at the ends of roads R4, R5, R2, and R3, starting from the top in the figure, are different from one another, so that the positions at which the ends of each road are difficult to see do not line up vertically in a straight line. Therefore, when such a screen is viewed through the half-mirror area of the mirror member 13, it is possible to make the viewer less aware of the edges of the screen.

In addition, since the positions of the ends of each road are no longer aligned in a straight line parallel to the edges of the screen of the display unit 14 at the screen edge, no subjective contours (coincident with or parallel to the edges of the screen of the display unit 14) connecting the ends of each road are generated, and the screen area of the display unit 14 can be made unconscious. In particular, when drawing multiple objects close to the edge of the screen, it is advisable to determine the positions of the ends of the objects so that the virtual lines connecting the ends of the multiple objects in a direction parallel to the edge of the screen are not parallel to the lines of the edge of the screen. For example, it is advisable to set the lines connecting the positions where the roads completely disappear by gradation processing (for example, virtual lines connecting in order from X=0 to X=m, or virtual lines connecting in order from Y=0 to Y=m) in random positions so that they are not parallel to the four sides of the screen.

The starting position of the gradation may also be set in the same way. In other words, the starting position of the gradation of an object may be determined so that a virtual line connecting the gradation starting positions of multiple objects in a direction parallel to the edge of the screen is not parallel to the edge of the screen. Furthermore, it is advisable to make the gradation pattern (for example, how far it should be and how dark it should be) different for each object. By doing this, it is possible to prevent the occurrence of subjective contours parallel to the edge of the screen, making the edge of the screen less noticeable.

In application example 2, the display of the road changes in response to the movement of the vehicle, so the gradation data described above cannot be determined in advance. For this reason, when displaying a road object, the CPU 260 identifies roads that reach the edge of the screen, and for each road that reaches the edge, it arbitrarily determines the width of the gradation from the edge of the screen. Then, it performs a process to add a gradation of the determined width to each road. As described above, this process gradually reduces the brightness of the pixels involved in drawing the road as they approach the edge of the screen, or increases the number of pixels that display the same as the background image.

In addition, in the above example, the object is a "road," but similar processing may be performed for other objects (e.g., text). For example, when displaying a certain text, the CPU 260 determines whether the entire text is displayed on the screen. If it is determined that the entire text is displayed on the screen, no gradation is added to the text. In contrast, if it is determined that the text is partially cut off by the screen, for example because the vehicle has moved, a gradation of any width is added to the text.

(Application Example 3 of the First Embodiment)
In the above-mentioned Application Example 2, the range of the gradation area G within the screen is changed for each object displayed as an image. In contrast, in Application Example 3, the brightness gradient of the gradation is changed for each display color of each object.

Figure 7(b) shows an example of the display mode of an image in application example 3. The image shown in this figure is basically the same as the image shown in Figure 4, but in order to more clearly illustrate the features of application example 3, the icon display area 140B is not shown. Also, in this figure, the same parts as those shown in Figure 4 are given the same reference numerals and detailed explanations are omitted. Note that in Figure 7(b), the roads in the map 151, various icons (own vehicle icon 152, warning target icon 153), legal speed limit 154, current speed 155, and other numbers and lines displayed as images are treated as individual objects.

In the image of map 151 shown in FIG. 7(b), road GR, which extends vertically in the approximate center of the screen, is generally displayed in green, a color that is easily detected by the human eye (a color with high sensitivity). Road BR, which extends horizontally from the left edge of the screen toward the center and meets the above-mentioned road GR, is generally displayed in blue, a color that is difficult for the human eye to detect (a color with low sensitivity). Furthermore, areas other than roads are displayed in a color with intermediate sensitivity between green and blue (e.g. orange).

As shown in FIG. 7(b), the width Wa of the gradation area for the road GR, an object displayed in a highly sensitive color (corresponding to the "periphery of the object") is wider than the width W of the gradation area G in areas other than the road. This is because the road GR is displayed in a color that is easily detected by the human eye, so by starting the gradation at a position farther away from the edge of the screen, the apparent change in brightness of the road GR can be made to match the apparent change in brightness of the areas other than the road GR.

Conversely, the width Wb (corresponding to the "periphery of the object") of the gradation area for the road BR, an object displayed in a low-sensitivity color, is narrower than the width W of the gradation area G in areas other than the road. This is because the road BR is displayed in a color that is difficult for the human eye to detect, so by starting the gradation at a position closer to the edge of the screen, it is possible to match the apparent change in brightness of the road BR with the apparent change in brightness of areas other than the road BR.

In this way, by adding a gradation according to the display color of each "road" object on the displayed map, it is possible to adjust the change in brightness of the image in the gradation area G so that it becomes uniform when the screen is viewed as a whole.

Second Embodiment
A second embodiment for adding a gradation region G to a displayed image is shown in Fig. 8. Fig. 8 shows a schematic exploded perspective view of the display unit 14. In this figure, the liquid crystal panel 50 is a well-known liquid crystal panel constituting a rectangular screen for displaying an image, and is composed of a liquid crystal layer, a transparent electrode, a color filter, a polarizing plate, and the like. The illumination means 51 illuminates the liquid crystal panel 50 from behind in order to make the image displayed on the liquid crystal panel 50 visible, and is composed of a rod-shaped cold cathode tube 52 and a rectangular light guide plate 53. The cold cathode tube 52 is provided along one short side of the light guide plate 53, and the light guide plate 53 takes in the light of the cold cathode tube 52 from the short side cross section on the side where the cold cathode tube 52 is provided, and emits it from the surface on the liquid crystal panel 50 side, thereby illuminating the liquid crystal panel 50 from behind.

The gradation adding filter 54 is a sheet-like filter for adding the gradation area G shown in FIG. 4 to the image displayed on the liquid crystal panel 50, and its shape and dimensions match the image display area of the liquid crystal panel 50. The gradation adding filter 54 is formed so that in the area corresponding to the gradation area G shown in FIG. 4, the light transmittance gradually decreases from the boundary (shown by the dashed line in FIG. 4) toward the periphery of the gradation adding filter 54, and a light-blocking state is achieved when the periphery is reached. Note that it is desirable to make the light transmittance in the normal area N of the gradation adding filter 54 as high as possible. Also, for example, the normal area N may be cut out to form a rectangular frame-shaped sheet having a certain width W.

The gradation adding filter 54 corresponds to a "transmittance reducing means" that reduces the brightness of the image displayed on the liquid crystal panel 50 according to the light transmittance in the gradation region G.

(Modification of the second embodiment)
8, the gradation adding filter 54 is disposed on the front surface (the surface facing the driver) of the liquid crystal panel 50, but as a modification, the gradation adding filter 54 may be disposed between the liquid crystal panel 50 and the lighting means 51 (on the rear surface side of the screen). In this case, the gradation adding filter 54 functions as a "light reducing means" that reduces the light from the lighting means 51 in accordance with the light transmittance in the gradation region G.

In addition, instead of providing the gradation adding filter 54 shown in FIG. 8, the light transmittance in the half mirror region HM of the mirror member 13 in the region corresponding to the gradation region G shown in FIG. 4 may be gradually changed. In addition, in the gradation adding filter 54, the boundary B between the normal region N and the gradation region G shown in FIG. 4 may be a curve that varies within a predetermined range, like the boundary B' shown in FIG. 5.

Third Embodiment
Fig. 9 shows a third embodiment for adding a gradation region G. In the above-mentioned second embodiment, a gradation adding filter 54 is added to the configuration of the display unit 14, but in this embodiment, instead of adding a gradation adding filter 54, a feature is added to the lighting means 51 constituting the display unit 14. Here, Fig. 9 is a front view showing the appearance of the lighting means 51 (see Fig. 8) constituting the display unit 14, (a) showing a schematic diagram of a general lighting means, and (b) showing a schematic diagram of the lighting means in the second embodiment. In this figure, the same components as those shown in Fig. 8 are assigned the same reference numerals, and detailed description thereof will be omitted.

First, the light guide plate 53a shown in FIG. 9(a) is used for a general lighting means 51 (for example, the lighting means shown in FIG. 8). On the surface of this light guide plate 53a opposite to the surface facing the liquid crystal panel (hereinafter referred to as the back surface), a large number of white dots WD are formed to reflect the light incident from one short side of the light guide plate 53a toward the back surface of the liquid crystal panel. The white dots WD are formed, for example, by printing white ink on the back surface of the light guide plate 53a, and in this embodiment, they are circular in shape. In order to illuminate the back surface of the liquid crystal panel with as uniform brightness as possible, the size and density of the white dots WD are smaller and sparser the closer they are to the cold cathode fluorescent lamp 52, which is the light source, and larger and denser the farther they are from the light source.

On the other hand, in the case of the light guide plate 53a of the third embodiment shown in FIG. 9(b), the size and density of the white dots WD in the normal region N within the dashed line in the figure show a tendency similar to that of the general light guide plate 53a shown in FIG. 9(a). In contrast, in the gradation region G shown by hatching, compared to the white dots WD shown in FIG. 9(a), the closer to the edge of the light guide plate 53b, the smaller and sparser the dots tend to be. By forming the white dots WD on the back surface of the light guide plate 53b in this way, the image displayed in the gradation region G can be displayed so that it gradually becomes darker as it approaches the edge of the screen.

That is, by forming the white dots WD in the "normal area N" corresponding to the "central illumination area" and the "gradation area G" corresponding to the "peripheral illumination area" as in the light guide plate 53b shown in FIG. 9(b), it is possible to "make the amount of light in the peripheral illumination area less than the amount of light in the central illumination area." Note that in FIG. 9(b), the boundary B between the normal area N and the gradation area G is shown as a straight line, but the size and arrangement density of the white dots WD may be determined so that it becomes a curve that varies within a predetermined range, like the boundary B' shown in FIG. 5.

(Modification of the third embodiment)
9 is mainly composed of cold cathode fluorescent lamps and a light guide plate, but instead, for example, a substrate on which a plurality of white LEDs are arranged in a matrix may be provided behind the liquid crystal panel, and the brightness of each white LED may be made adjustable.Then, by adjusting the amount of light of each white LED arranged in the area corresponding to the gradation area G to be less than the amount of light of each white LED arranged in the area corresponding to the normal area N, it is possible to make the "amount of light of the peripheral illumination section less than the amount of light of the central illumination section."

This brightness adjustment is possible by changing the current supplied to the LED, or by using pulse width modulation (PWM) to change the time during which current is supplied to the LED (pulse width) and the ratio of the time during which current is supplied to the LED to the time during which it is not (duty ratio). In this way, the means for making it possible to adjust the brightness of each white LED is included in the "brightness adjustment means".

<Other changes>
The "mask means" in the display device according to the present invention is not limited to the area consisting of the mirror area M and the half mirror area HM formed on the mirror member 13 functioning as a room mirror in the vehicle as in the above-mentioned embodiment. For example, the mirror area M may also be configured as the half mirror area so that the entire area of the mirror is configured as the half mirror area. In addition, a transparent member with a reduced light transmittance, such as smoked glass installed on the driver's side of an image display device or various instruments in an instrument panel of a vehicle (so-called instrument panel), is also included in the "mask means" of the present invention. In this case, it is preferable that the smoked glass is configured to include an area facing the screen and have an area having a predetermined width around the area. In this way, it is possible to make it difficult to feel the screen area not only when an image is not displayed on the screen but also when an image is displayed on the screen. This gives the viewer of the image the impression that the entire area of the mask means is the screen of the display device.

<Action and Effects>
The half mirror area HM and the mirror area M work to make the screen boundary less noticeable when the liquid crystal of the display unit 14 is turned off, thereby increasing the sense of unity between the mirror and the liquid crystal. However, in the conventional configuration, as soon as the liquid crystal of the display unit 14 is turned on, the screen boundary becomes noticeable, and it looks as if a square photo or picture sticker has been stuck on the mirror area M, which is uninteresting. One of the reasons for this is that the image is clearly displayed up to the square frame at the edge of the screen. According to the configuration of each of the above-mentioned embodiments, when the screen is viewed through the half mirror area HM, the square liquid crystal frame at the edge of the screen is not felt, so the image, letters, etc. appear to be floating on the mirror. In other words, the masking means consisting of the half mirror area HM and the mirror area M can have a stronger sense of unity with the image.

REFERENCE SIGNS LIST 10 Radar detector 11 Housing 12a, 12b Fixture 13 Mirror member 14 Display unit 14 (display means)
15 Infrared receiving unit 17 Speaker 18 Sound emission hole 19 Insertion hole for DC power jack 20 Slot 21 GPS receiver 22 Microwave receiver 23 Radio receiver 24 Memory card reader 25 Memory card 26 Control unit (brightness adjustment means, storage means, data writing means, image display means)
27 Database 28 Remote control 50 Liquid crystal panel 51 Illumination means 52 Cold cathode fluorescent tube 53 Light guide plate 54 Gradation addition filter (transmittance reduction means, dimming means)
140 Screen display area 140A Main display area 140B Icon display area 141 Speed 142 Latitude 143 Longitude 144 Compass icon 145 Road selection icon 146 Radar reception sensitivity mode icon 147 Mode selection icon 148 Current time 151 Map 152 Vehicle icon 153 Warning target icon 154 Legal speed 155 Current speed of vehicle

Claims (2)

A function of displaying an object on a screen based on image data;
The function of displaying is
a display device which, when a part of the object is not displayed within the screen, displays the object in a gradation so that the brightness of the peripheral part of the screen of the object is lower than the brightness specified by the image data. A program for causing a computer to realize the display function of the display device described in claim 1.