JPH0797824B2 - Image processing device - Google Patents

Description

The present invention relates to an image processing device, and more particularly to a characteristic conversion process for converting a characteristic of an input image signal.

[Prior Art] An image processing apparatus which compares the levels of a multi-valued image signal and a predetermined pattern signal to form a pulse width modulated image signal and forms an image based on the image signal has already been proposed by the present applicant.
FIG. 5 is a block diagram of the image processing apparatus proposed by the applicant of the present application. The image processing apparatus includes an optical reading device 1 such as a CCD Sukiyana for outputting connexion analog image signal VA ₁ reading an original image, the analog image signal VA ₁ and A / D converter 2 for converting the digital image signal VD ₁ , A γ-conversion unit 30 for gamma (γ) -correcting the digital image signal VD ₁ to output a corrected digital image signal VD ₂ ′ to obtain a constant density image characteristic from the luminance image information, and the corrected γ-conversion unit 30 D / A that converts digital image signal VD ₂ ′ to analog image signal VA ₂ ′
A converter 4, a pattern signal generating means 5 for generating a predetermined pattern signal PS for comparison, and the analog image signal
A comparator 6 for forming a binary image signal PW which is pulse width modulated by comparing the level of VA ₂ ′ and the pattern signal PS, and a beam of a laser beam printer or the like based on the binary image signal PW. A laser driver 7 for controlling ON / OFF is provided. By this method, the applicant of the present invention has obtained an image having a very excellent gradation, which is superior to the conventional analog copying machine.

[Problems to be Solved by the Invention] However, upon further study, the following inconveniences have occurred in practical use. In short, it is impossible to obtain an image with a desired density because there is no suitable density adjusting means. The details will be described below.

6 to 8 relate to the inconvenience when trying to adjust the density in the proposed device, FIG. 6 is the operation timing chart of the device of FIG. 5, and FIG. 7 is the case of lowering the pattern signal level. And FIG. 8 is an explanatory view of the inconvenience that occurs when the pattern signal level is raised. As described above, the apparatus of FIG. 5 forms the pulse width modulated binary image signal PW by comparing the levels of the analog image signal VA ₂ ′ and the pattern signal PS. For example, as shown in FIG. The laser beam is turned on only at a place where the level of the pattern signal PS is higher than the level of the analog image signal VA ₂ ′, and although not shown in the figure, the printing portion on the pre-charged photoconductor is exposed to expose the electrostatic latent image. Form an image,
Then, the exposed portion is developed by a reversal development method, then transferred to plain paper by a corona transfer method or the like, fixed, and discharged to the outside of the apparatus.

Now, referring to FIG. 7, for example, the analog image signal VA ₂ ′
Is close to the white level, and you may want to skip (whiten) such an image in such a light area. In such a case, the level of the pattern signal PS may be shifted downward as it is to form the pattern signal PS '. However, in this case, when the analog image signal of the black level comes, the laser beam is lit up only for the pulse width t ₁ , so that a so-called solid black state cannot be obtained. In this way, when the image of the light portion is skipped, the density of the dark portion is lowered.

On the other hand, on the other hand, there are cases where it is desired to make the image of the light portion darker or thicker. In such a case, as shown in FIG. 8, the level of the pattern signal PS may be shifted upward as it is to form the pattern signal PS ″. As a result, the original level of the analog image signal VA ₂ ′ having a low level may be changed. Since the pulse width t ₂ is expanded in the direction of the arrow a, it can be made relatively thick or thick, but if this is done, the laser beam will be turned on even when an image signal of a white level is received, so that a so-called solid white state is obtained. Instead, the image becomes black with fog on the white background.

The above-mentioned drawback is development which similarly occurs in a conventional analog copying machine, although the density adjusting method is different. Further, although there is a dither method as a method for obtaining a high gradation conventionally, a plurality of dither ROMs are used as a density adjusting method in this dither method.
There is a method in which the gradation pattern is changed by selecting one of them to select the density. However, the dither method has a drawback that the resolution is extremely lowered and characters and the like are hardly readable, and it can be applied only to images such as photographs.

The present invention has been made in view of the above-mentioned drawbacks,
The point is that the user can adjust the characteristics of the input image signal to obtain a reproduced image desired by the user,
An object of the present invention is to provide an image processing device that can automatically obtain an optimum reproduced image by automatically adjusting an image signal.

[Means for Solving the Problems] In order to achieve the above object, the image processing apparatus of the present invention has the following configuration. That is, input means for inputting an image signal, density conversion means for converting the density characteristics of the image signal input by the input means using a conversion table, and density distribution of the image signal input by the input means are detected. Adjustment having a density detecting means for adjusting, a manual adjusting mode for adjusting the conversion characteristic of the density converting means by a manual operation, and an automatic adjusting mode for adjusting the conversion characteristic of the density converting means according to the output of the density detecting means. Means, and a switching means for selectively switching between a manual adjustment mode and an automatic adjustment mode, wherein the density conversion means has a plurality of conversion tables having different conversion characteristics, and the adjustment means includes the manual adjustment mode and In both of the automatic adjustment modes, select a desired conversion table from the plurality of conversion tables

[Operation] With the above configuration, in order to convert the density characteristic of the image signal, either the manual adjustment mode or the automatic adjustment mode is selected, the user manually selects the manual adjustment mode, and detects the automatic adjustment mode. The conversion characteristic is automatically adjusted according to the density distribution of the image signal thus adjusted, and the density characteristic of the input image signal is converted using a conversion table according to the adjusted conversion characteristic.

Embodiments Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

1 to 4 relate to the description of an embodiment of the present invention.
FIG. 1 is a block diagram of the image forming apparatus of the embodiment, and FIGS. 2 to 4 are graphs showing some examples of .gamma. Conversion patterns. The same components as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, when it is desired to adjust the density manually, switch 92 is opened and the automatic density adjustment mode signal AUTO
Set / (/ indicates negative logic) to logic "1". As a result, the data selector 10 selects the B side input and outputs the manually set adjustment amount (address) MA. For example, the manual adjustment of the concentration is performed by the operation unit 93 such as the concentration adjustment dial or lever.
Done in. The constant voltage (+ V) is divided by a variable resistor that is interlocked with the operation unit 93, and is output as a voltage VC corresponding to the operation amount. The A / D converter 91 digitally converts this voltage VC to form an adjustment amount MA. The adjustment amount MA works to determine the upper address UA of the characteristic conversion ROM 3 and select any one of the γ conversion patterns P0 to Pn. On the other hand, the digital image signal VD ₁ determines the lower address LA of the characteristic conversion ROM 3. Therefore, an arbitrary density conversion characteristic is determined by the upper address UA, and the digital image signal VD ₁ is read out as the density-converted digital image signal VD ₂ .

In the description of FIGS. 2 to 4, the digital image signals VD ₁ and VD ₂ are represented by 6 bits for simplification, and “00” H (H
Is a white level, and "3F" H is a black level. Therefore, the relationship between the white level and the black level is reversed from the relationship shown in FIGS. 6 to 8, but if the digital image signal VD ₂ is inverted at an appropriate place, it can be applied to the above-described inversion development method. In FIG. 2, for example, the conversion pattern P4 is a normal case where density conversion is unnecessary. In this embodiment, the operation unit 93
Is the base point of the density adjustment when the conversion pattern P4 is selected. Next, when it is desired to skip (whiten) the portion having a low density, the density adjustment dial 93 is used to move the selection of the γ conversion conversion pattern characteristic toward P5, P6, P7, P8. For example, when it is desired to skip the image from white to "0F" H, the conversion pattern P5 may be selected. The image signal VD ₁ of “05” H is output as the image signal VD ₂ of “00” H after conversion, so that it can be skipped completely. Even in this case, since the "3F" H image signal VD ₁ is directly converted to the "3F" H image signal VD ₂ , the so-called solid black density does not decrease. Moreover, since the level in the vicinity of "3F" H is converted into the vicinity of "3F" H almost as it is, the image density in the dark region is preserved and only the image in the light portion can be skipped. Next, when it is desired to skip the image signal VD _{1 up} to “2F” H, the γ conversion pattern P8 is selected. In this way, the image signal VD ₁ up to “2F” H can be skipped while maintaining the solid black density.

On the contrary, if you have an image of a light portion, you may want to make it darker. In this case, change the γ conversion pattern to P3, P2, P
Select in the direction of 1, P0. For example, if you select the conversion pattern P2 is "0F" image signals VD ₁ of H is "23" image of a thin portion becomes dark because it is converted into an image signal VD ₂ of H, is put out and Tsukiri. Moreover, the image signal VD ₁ of "00" H is "00" as it is.
Since it is converted into the H image signal VD ₂ , no background fog occurs.

That is, in the density adjustment of the present embodiment, even if the operation unit 93 is moved from its base point to the side of lighter density, the image density of the dark portion does not decrease, and conversely, even if it is moved from its base point to the side of darker density, No fog occurs. Although such density adjustment is desired for this type of image processing apparatus, it has not been possible in the past.

FIG. 3 shows an example of another conversion pattern. Here, the conversion patterns P0 to P4 work in the same manner as in FIG. However, the conversion patterns P5 to P8 are different. When the selection is advanced in the direction of the conversion patterns P4, P5, P6, and P7, the image in the light portion tends to become lighter and the image in the dark portion tends to become darker. If this tendency is further strengthened and, for example, the conversion pattern P8 is selected, the intermediate density is divided into white or black, and there is a tendency of being polarized.

That is, when the operation unit 93 is moved from the base point (conversion pattern P4) to the conversion pattern P5 side, the image density of the multi-valued image signal increases to the side where the predetermined density is increased to the side where the white density and the black density increase, respectively.
It will be polarized. According to this adjustment, the line drawing and the characters can be extracted from the color original or the original that is soiled, or the original can be reproduced in a sticky manner. Although such density adjustment is desired for this type of image processing apparatus, it has not been possible in the past.

FIG. 4 shows another example of the conversion pattern. Here, the same density adjustment as that shown in FIG. 2 can be performed, and .gamma. Correction and various device-specific corrections can be collectively performed. Therefore, the ideal density adjustment of the final result product can be performed, and the effect is excellent especially when dealing with complicated color signals.

Next, when it is desired to automatically perform the density adjustment, the switch 92 is closed and the automatic density adjustment mode signal AUTO / is set to logic "0". As a result, the data selector 10 selects the input A side and outputs the automatically set adjustment amount AA to the ROM 3. In the automatic density adjusting means 8, the density detecting section 81 obtains the average density from the maximum and minimum image signal densities for each main scanning line or more, or collects all the densities to obtain the average density. Alternatively, the density histogram is aggregated to obtain the density distribution. Of course, a predetermined area or one screen may be totaled. Next calculated concentration signal VDH
Address the density adjustment ROM 82 with. In the density adjustment ROM 82, density adjustment information correlated in advance with the density signal VDH is written in a table. For example, when the total aggregated average density is high, or when the density distribution is concentrated in a dark area, the patterns P5, P6, P7, etc. of FIG. 2 are correlated so as to be automatically selected. When the density distribution is polarized into a light portion and a dark portion, the patterns P5, P6, P7, etc. in FIG. 3 are correlated so as to be automatically selected. In this way, the data AA read from the ROM 82 changes, for example, the γ conversion pattern used for the next main scanning line in real time.

The various γ conversion patterns shown in FIGS. 2 to 4 are merely examples, and it goes without saying that various other γ conversion patterns can be considered.

Further, in the present embodiment, various γ conversion patterns are selected, but the density conversion characteristics may be changed by electronic circuit parameters.

[Effects of the Invention] As described above, the image processing apparatus of the present invention allows the user to manually adjust the characteristics of the input image signal in the manual adjustment mode or automatically in the automatic adjustment mode. In each mode, a reproduced image desired by the user can be obtained, and an optimum reproduced image can be automatically obtained, which has the effect of improving operability.

Further, since the common conversion table is used in the manual adjustment mode and the automatic adjustment mode, it is possible to prevent an increase in the required memory capacity without increasing the number of conversion tables.

Further, since the conversion table used for converting the characteristics of the input image signal is selected from a plurality of conversion tables set in advance, the conversion characteristics can be set instantaneously,
The conversion process can be spoiled quickly.

[Brief description of drawings]

FIG. 1 is a block diagram of the image forming apparatus of the embodiment, FIGS. 2 to 4 are graphs showing several examples of .gamma. Conversion patterns, and FIG. 5 is an image forming apparatus already proposed by the applicant. FIG. 6 is a block configuration diagram of FIG. 6, FIG. 6 is an operation timing chart of the apparatus of FIG. 5, FIG. 7 is an explanatory diagram of inconvenience caused when the pattern signal level is lowered, and FIG. 8 is caused when the pattern signal level is raised. It is explanatory drawing of inconvenience. In the figure, 1 ... CCD scanner, 2,91 ... A / D converter, 3 ...
Characteristic conversion ROM, 4 ... D / A converter, 5 ... Pattern signal generating means, 6 ... Comparator, 7 ... Laser driver, 8 ...
Automatic concentration adjustment means, 9 ... Manual concentration adjustment means, 10
…… Data selector, 93 …… Operation part, 94 …… Variable resistor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Moto Kato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsuo Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Yukihiro Ozeki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takahiro Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 56) References JP 60-153263 (JP, A) JP 60-125064 (JP, A) JP 60-84085 (JP, A) JP 56-1666 (JP, A)

Claims (1)

[Claims] 1. An input unit for inputting an image signal, a density conversion unit for converting a density characteristic of the image signal input by the input unit using a conversion table, and a density of the image signal input by the input unit. Density detection means for detecting the distribution, a manual adjustment mode for adjusting the conversion characteristics of the density conversion means by manual operation, and an automatic adjustment mode for adjusting the conversion characteristics of the density conversion means according to the output of the density detection means. And a switching means for selectively switching between a manual adjustment mode and an automatic adjustment mode, wherein the density conversion means has a plurality of conversion tables having different conversion characteristics, and the adjustment means is the manual operation mode. A desired conversion table is selected from the plurality of conversion tables in both the adjustment mode and the automatic adjustment mode. The image processing apparatus characterized by.