JP3789658B2 - Analog video signal AD conversion method and plasma display device driving method using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AD conversion method when converting an analog video signal into a digital signal, and more particularly to an AD conversion method in a driving method of a plasma display device using a subfield method.
[0002]
[Prior art]
For example, a plasma display device, which is expected to be widely used as a digital display device, uses a sub-field method in which one frame is formed from a plurality of sub-fields having different luminance relative ratios (weighting) to display in multiple gradations. The drive system has a configuration as shown in FIG.
[0003]
According to the configuration shown in the figure, an analog video signal is digitally converted by an AD converter (analog / digital converter). In this AD converter, the standard amplitude (theoretical luminance range) of the video signal is black. The amplitude from level (standard minimum luminance level) to white level (standard maximum luminance level) is AD converted according to the number of display gradations. Based on this digital signal, a drive signal is generated by a subfield method to drive a plasma display panel (PDP).
[0004]
[Problems to be solved by the invention]
In AD conversion in the conventional driving method as shown in FIG. 1, the display gradation is determined in accordance with the theoretical luminance range of the video signal. For this reason, for example, when the dynamic range of luminance (actual luminance range) on the actual display screen is narrower than the theoretical luminance range, the gradation corresponding to the difference between the theoretical luminance range and the actual luminance range is not displayed. As a result, the number of display gradations on the actual screen is reduced, resulting in a decrease in image quality. Specifically, in a scene where the actual luminance range is biased toward the black level, such as in a dark scene, the gradation near the white level is not used, so the number of gradations not used is the actual display gradation. As a result of the decrease, there is a problem that the luminance change is not felt and the black color is lost and the translation is unknown.
[0005]
Therefore, the present invention provides an analog video signal AD conversion method that can be adjusted so that the number of gradations in the actual luminance range is as large as possible, and this method is applied to the driving method of the plasma display device.
[0006]
[Means for Solving the Problems]
The present invention that solves such a problem is characterized in that the threshold value of AD conversion is changed according to a predetermined operation in AD conversion using an analog video signal as a digital signal. That is, the threshold value for AD conversion is a threshold value at which the display gradation shifts to the next stage, and this means the level of an analog signal at which the digital value is increased during AD conversion.
[0007]
According to this, for example, in a digital still camera, a digital video camera, or a digital VTR, a night view button is provided for a predetermined operation, and the AD conversion threshold is set to a black level as a whole by operating the night view button. Can be shifted toward As a result, when the night view button is operated, for example, the AD conversion of all gradations can be performed within the range of the half of the black level with respect to the normally set theoretical luminance range, and the number of gradations at low luminance can be reduced. It can increase and increase the definition. Therefore, it becomes possible to record and reproduce a dark scene such as a night view without being blacked out. If a digital display device is equipped with the same button, the number of display gradations can be reduced by shifting the threshold value for AD conversion to the black level by operating the button when there are many dark scenes that are difficult to see. It can be increased to increase the definition and make it easier to see.
[0008]
Furthermore, in the present invention, when AD conversion using an analog video signal as a digital signal, a luminance distribution in the analog video signal to be converted is detected, and a threshold value for AD conversion is changed in accordance with the luminance distribution. And In other words, the threshold value change according to the above-mentioned predetermined operation is automatically controlled by detecting the luminance distribution, and digital images that can be automatically adjusted by detecting extremely bright or extremely dark scenes. Equipment can be provided. At this time, it is also possible to provide a brightness detection button or the like so that automatic adjustment control can be turned on and off. The luminance distribution in this case can be appropriately realized by a technique such as detecting the amplitude of the analog video signal.
[0009]
The present invention provides a driving method for a plasma display device to which the analog video signal AD conversion method as described above is applied. That is, in the driving method of a plasma display device that forms one frame from a plurality of subfields having different luminance relative ratios and performs multi-gradation display, AD conversion using an analog video signal as a digital signal is performed according to a predetermined operation. The conversion threshold value is changed. Alternatively, when AD conversion using an analog video signal as a digital signal, a luminance distribution in the analog video signal to be converted is detected, and a threshold value for AD conversion is changed in accordance with the luminance distribution.
[0010]
In this way, by detecting the luminance distribution of the display screen (one screen or more) by the video signal, the actual luminance range is grasped, and the AD conversion threshold value is changed in accordance with the actual luminance range. For example, when the theoretical luminance range of the video signal is 0 to 1 V, in a scene where the actual luminance range is extremely biased toward the black level, each threshold value is shifted toward the black level (low level). Adjustment can be made so that all gradations are converted in a gradation display range of 0 to 0.5V. Therefore, if the theoretical luminance range is 256 gradations, all 256 gradations can be used even in the actual luminance range, and the image quality can be maintained.
[0011]
In such a plasma display apparatus driving method, it is preferable to reduce the number of light emission pulses in a predetermined subfield when the maximum luminance level of the detected luminance distribution is lower than the white level. That is, for example, when adjustment is made to adapt to a scene biased to the black level, if the maximum brightness after adjustment is the same as the white level, that is, the standard maximum brightness level in the theoretical brightness range, the scene that should be dark will become abnormally bright. Will not match other scenes. Therefore, in this case, the light emission period in all gradations is shortened by reducing the number of light emission pulses in all subfields, and control is performed to darken the whole. The opposite is also true for the black level. Therefore, when the minimum luminance level of the detected luminance distribution is higher than the black level, it is preferable to increase the number of light emission pulses in a predetermined subfield.
[0012]
According to this, when the luminance distribution is concentrated between the black level and the white level, the number of emission pulses is reduced from the maximum luminance to the central luminance of the distribution, while the number of emission pulses is from the lowest luminance to the central luminance. Can be adjusted so as to approach the center level of the actual luminance range.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a block diagram showing an example of the configuration of the main part of a driving type plasma display apparatus employing the AD conversion method of the present invention.
[0014]
The luminance distribution detector that inputs an analog video signal detects the luminance distribution in the input video signal, and the AD conversion threshold in the AD converter is adjusted based on this data. The luminance distribution detection unit also detects the minimum luminance level and the maximum luminance level of the input video signal, and the pulse number changing unit controls the subfield configuration unit based on this data to adjust the number of light emission pulses in the subfield. .
[0015]
FIG. 3 shows a specific example of an AD converter that can adjust the threshold value. The illustrated example is a parallel comparison type using comparators COM1 to COM7, and has a configuration of 3 bits and 8 gradations. By controlling the resistance values of the variable resistors R1 to R8 according to the detection result of the luminance distribution detector, the reference voltage Vref of each of the comparators COM1 to COM7 can be changed, and therefore each comparison of video signals that are analog inputs is possible. Level = threshold can be changed. Thereby, the gradation display range shown in FIGS. 4 to 8 can be adjusted.
[0016]
4 to 8 show examples of adjustment when the theoretical luminance range of the video signal is set to 0 to 1 V. A partial diagram A shows a state of AD conversion, and a partial diagram B shows a luminance distribution. .
[0017]
FIG. 4 shows an example in which the theoretical luminance range and the actual luminance range match, that is, the luminance distribution is averaged. Since any level of luminance is present on average in one screen, the threshold value for AD conversion is not adjusted. Therefore, a normal gradation display range corresponding to the theoretical luminance range is set. The
[0018]
FIG. 5 shows an example when the luminance distribution is biased toward the black level. This is a scene in which one screen is entirely dark, such as a dark scene, and if the standard specification of FIG. 4 is used as in the prior art, only about half of the eight gradations are used. Therefore, in this example, when such a luminance distribution is detected by the luminance distribution detector, control is performed so that the resistance value of the resistor R1 in FIG. 3 is large and the resistance values of the other resistors R2 to R8 are small. As a result, the threshold value for AD conversion is changed, and adjustment for narrowing the gradation display range toward the lower level is performed. As a result, for example, all 8 gradations are used within a gradation display range of 0 to 0.6 V, and the image quality is maintained.
[0019]
At this time, if the maximum luminance level becomes the same as the white level, the luminance level (0.6 V), which is the middle in FIG. 4, becomes equal to the white level (1 V), and the screen is abnormally displayed. It becomes bright and does not match other scenes. Therefore, adjustment is performed by the pulse number changing unit that receives data from the luminance distribution detection unit, and the light emission period is shortened by reducing the number of light emission pulses in each subfield, so that overall higher luminance is lowered. Is done.
[0020]
FIG. 6 shows an example when the luminance distribution is biased toward the white level. This is a scene where the entire screen is bright, such as a scene taken of the sky. When such a luminance distribution is detected by the luminance distribution detector, the resistance value of the resistor R8 in FIG. 3 is large, and the other resistor R1. By adjusting the resistance values of .about.R7 to be small, the threshold value for AD conversion is changed to adjust the gradation display range to a higher level. As a result, for example, all eight gradations are used within a gradation display range of 0.4 to 1 V, and the image quality is maintained.
[0021]
At this time, if the minimum luminance level is the same as the black level, the luminance level (0.4V), which is the middle in FIG. 4, becomes equal to the black level (0V), and the screen is abnormally displayed. It becomes dark and no longer matches other scenes. Therefore, adjustment is performed by the pulse number changing unit that receives data from the luminance distribution detection unit, and the light emission period is lengthened by increasing the number of light emission pulses in each subfield so that the overall lower luminance is increased. Is done.
[0022]
FIG. 7 shows an example where the luminance distribution is concentrated between the black level and the white level. This is a scene where there is no bright and dark poles in one screen, and when such a luminance distribution is detected by the luminance distribution detector, the resistance values of the resistors R1 and R8 in FIG. By adjusting the resistance value of R7 to be small, the threshold value for AD conversion is changed to adjust the gradation display range to an intermediate level. As a result, for example, all eight gradations are used within a gradation display range of 0.2 to 0.8 V, and the image quality is maintained.
[0023]
At this time, if the highest luminance level is the same as the white level and the lowest luminance level is the same as the black level, the bright areas on the screen are significantly brighter and the dark areas are significantly darker. A difference comes out and it doesn't match with other scenes. Therefore, adjustment is performed by the pulse number changing unit that receives data from the luminance distribution detecting unit, and light emission is performed in the lower subfield from the lowest luminance level (0.2V) to the central luminance level (0.5V) of the distribution. While the number of pulses is increased, the upper side subfield from the central luminance level (0.5 V) to the maximum luminance level (0.8 V) is controlled to decrease the number of light emission pulses (the central luminance level is controlled by the number of light emission pulses). None). As a result, the brightness near the distribution center is approached as a whole, so that an abnormal contrast is prevented.
[0024]
FIG. 8 shows an example in which the luminance distribution is biased toward both the black level and the white level. This is a scene where there is an extreme brightness difference in one screen, and when such a luminance distribution is detected by the luminance distribution detector, the resistance values of the resistors R4 and R5 in FIG. 3 are large, and the other resistors R1 By adjusting the resistance values of .about.R3, R6.about.R8 to be small, the threshold value of AD conversion is changed, and the gradation display range is narrowed to the bipolar level, and the adjustment is made to leave the middle. As a result, for example, four gradations are used in both gradation display ranges of 0 to 0.3 V and 0.7 to 1 V, and all eight gradations are used, and the image quality is maintained. At this time, it is not necessary to change the number of light emission pulses.
[0025]
【The invention's effect】
According to the present invention, an optimum gradation display range corresponding to the luminance distribution of the display screen is set, and it is possible to use as many gradations as possible within the actual luminance range. Even in bright scenes, blackening and whitening are not lost, and the overall image quality can be improved. In addition, if the number of light emission pulses is not controlled in the case described with reference to FIG. 5, it becomes possible to intentionally brighten a dark scene so that it can be viewed brightly so that a night image can be clearly understood. Convenient applications such as are also possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a driving method of a conventional plasma display apparatus.
FIG. 2 is a block diagram showing a driving method of the plasma display device according to the present invention.
FIG. 3 is a circuit diagram showing an example of an AD conversion unit in FIG. 2;
FIG. 4 is an explanatory diagram showing AD conversion when the theoretical luminance range and the actual luminance range match.
FIG. 5 is an explanatory diagram showing AD conversion when the actual luminance range is biased toward the black level.
FIG. 6 is an explanatory diagram showing AD conversion when the actual luminance range is biased toward the white level.
FIG. 7 is an explanatory diagram showing AD conversion when the actual luminance range is concentrated to an intermediate level between a black level and a white level.
FIG. 8 is an explanatory diagram showing AD conversion when the actual luminance range is biased toward both the black level and the white level.

Claims (2)

In a driving method of a plasma display device that constitutes one frame from a plurality of subfields having different luminance relative ratios and performs multi-tone display,
At the time of AD conversion using an analog video signal as a digital signal, the luminance distribution in the analog video signal to be converted is detected, the threshold value for AD conversion is changed in accordance with the luminance distribution ,
When adjustment for narrowing the gradation display range to a lower level by changing the threshold value of AD conversion is performed, control is performed to reduce the number of light emission pulses in a predetermined subfield. Characteristic drive system. In a driving method of a plasma display device that constitutes one frame from a plurality of subfields having different luminance relative ratios and performs multi-tone display,
At the time of AD conversion using an analog video signal as a digital signal, the luminance distribution in the analog video signal to be converted is detected, the threshold value for AD conversion is changed in accordance with the luminance distribution ,
When adjustment is performed by changing the threshold value for AD conversion to narrow the gradation display range toward a higher level, control is performed to increase the number of light emission pulses in a predetermined subfield. Characteristic drive system.

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