JP2000134559A - Ad converting method for analog video signal and drive system of plasma display device utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AD converting method for an analog video signal capable of adjusting the number of gradations so as to be as many as possible in a dynamic range even when the range of luminance in an actual display screen is narrow. SOLUTION: The luminance distribution of a video signal is detected, and when the luminance distribution is biased to a black level, adjustment that reduces a gradation display range toward a low level is performed by changing AD conversion threshold of when the video signal is made into a digital signal. Consequently, all eight gradations are used within 0 to 0.6 V gradation display range that is narrower than 0 to 1 V normal range and image quality is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AD conversion method for converting an analog video signal into a digital signal.
In particular, the present invention relates to an AD conversion method in a driving method of a plasma display device using a subfield method.

[0002]

2. Description of the Related Art For example, a plasma display device, which is expected to be widely used as a digital display device, uses one or more subfields having different relative ratios (weightings) of luminance.
Although a subfield system for forming a frame and displaying multiple gradations is used, the driving system has a configuration as shown in FIG.

According to the configuration shown in the figure, an analog video signal is converted into a digital signal by an AD converter (analog / digital converter). In the AD converter, the standard amplitude (theoretical luminance range) of the video signal is used. ... The amplitude from the black level (standard minimum luminance level) to the white level (standard maximum luminance level) is AD-converted according to the number of display gradations. Then, a driving signal is generated by a subfield method based on the digital signal to drive a plasma display panel (PDP).

[0004]

In the AD conversion in the conventional driving method as shown in FIG. 1, a display gradation is determined in accordance with a theoretical luminance range of a video signal. For this reason, for example, when the dynamic range (actual luminance range) of the luminance on the actual display screen is narrower than the theoretical luminance range, the gradation of the portion corresponding to the difference between the theoretical luminance range and the actual luminance range is not displayed. In other words, the number of display gradations on the actual screen is reduced, and the image quality is reduced. 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. As a result, there is a problem that a change in luminance is not sensed, black is lost, and the meaning cannot be understood.

Accordingly, the present invention provides an analog video signal AD conversion method that can be adjusted so that the number of gray levels in the actual luminance range is as large as possible, and is applied to a driving method of a plasma display device.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an A / D converter for converting an analog video signal into a digital signal.
At the time of D conversion, a threshold value of AD conversion is changed according to a predetermined operation. The threshold value of the AD conversion is a threshold value at which the display gradation shifts to the next stage, which means a level of an analog signal at which a digital value is raised during AD conversion.

According to this, for example, a digital still camera, a digital video camera, or a digital VTR
In the above, a night view button may be provided for a predetermined operation, and the threshold of the AD conversion may be shifted toward the black level as a whole by operating the night view button. As a result, when the night view button is operated, for example, the A / D conversion of all gradations can be performed within the half range of the black level side with respect to the theoretical luminance range of the normal setting. It can increase the definition and increase the definition. Therefore, recording and reproduction can be performed without darkening even in dark scenes such as night scenes. Also, if the same button is provided on the digital display device, the number of display gradations can be reduced by shifting the threshold value of the AD conversion to the black level side by operating the button when there are many dark scenes and it is difficult to see. It is possible to increase the definition and to make it easier to see.

Further, according to the present invention, at the time of AD conversion in which an analog video signal is converted into a digital signal, a luminance distribution in the analog video signal to be converted is detected, and a threshold value of the AD conversion is changed in accordance with the luminance distribution. It is characterized by the following. In other words, the threshold value change according to the above-mentioned predetermined operation is automatically controlled by detecting a luminance distribution, and a digital image capable of automatically adjusting by detecting an extremely bright scene or an extremely dark scene. Equipment can be provided. At this time, it is also possible to provide a luminance detection button or the like so that the automatic adjustment control can be turned on / off. The luminance distribution in this case can be appropriately realized by a method such as detecting the amplitude of the analog video signal.

Further, the present invention provides a driving method of a plasma display device to which the above-described analog video signal AD conversion method is applied. In other words, in a driving method of a plasma display apparatus that forms one frame from a plurality of subfields having different relative ratios of luminance and performs multi-gradation display, an analog video signal is a digital signal.
At the time of D conversion, a threshold value of AD conversion is changed according to a predetermined operation. Alternatively, at the time of AD conversion that converts an analog video signal into a digital signal, a luminance distribution in the analog video signal to be converted is detected, and a threshold value of the AD conversion is changed in accordance with the luminance distribution.

As described above, the display screen (1) based on the video signal
By detecting the actual luminance range by detecting the luminance distribution of (screen or more) and changing the threshold value of the AD conversion according to the actual luminance range, for example, the theoretical luminance range of the video signal can be set to 0 to 0. In the case where the actual luminance range is extremely biased toward the black level when 1 V is set, each threshold is shifted toward the black level (low level), and the threshold is shifted in the gradation display range of 0 to 0.5 V. It can be adjusted so that conversion of all gradations is performed. 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.

In such a driving method of the plasma display apparatus, when the highest luminance level of the detected luminance distribution is lower than the white level, it is preferable to reduce the number of light emission pulses in a predetermined subfield. That is, for example, when adjustment is performed to adapt to a scene biased toward the black level, if the adjusted maximum luminance is the same as the white level, that is, the standard maximum luminance level in the theoretical luminance range, the scene that should be dark becomes abnormally bright. Will not match other scenes. Therefore, in this case, control is performed to reduce the number of light emission pulses in all subfields, thereby shortening the light emission period in all gradations and making the whole dark. Since the opposite is true for the black level, if the lowest 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.

According to this, when the luminance distribution is concentrated in the middle between the black level and the white level, the number of light emission pulses is reduced from the highest luminance to the center luminance of the distribution, while the number of light emission pulses is reduced from the lowest luminance to the center luminance. It is also possible to increase the number of light emission pulses and make adjustments so as to approach the center level of the actual luminance range.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram showing an example of the configuration of a main part of a driving type plasma display apparatus employing the AD conversion method of the present invention.

A luminance distribution detecting section for inputting an analog video signal detects a luminance distribution in the input video signal, and adjusts an AD conversion threshold in the AD converting section based on this data. In addition, the luminance distribution detection unit includes:
The minimum luminance level and the maximum luminance level of the input video signal are also detected, and based on this data, the pulse number changing unit controls the subfield forming unit, and the number of light emission pulses in the subfield is adjusted.

FIG. 3 shows a specific example of an AD converter in which the threshold value can be adjusted. The illustrated example is the comparators COM1 to COM7.
And a 3-bit, 8-gradation configuration. By controlling the resistance values of the variable resistors R1 to R8 in accordance with the detection result of the luminance distribution detection unit, the reference voltage Vref of each of the comparators COM1 to COM7 can be changed. Level = threshold can be changed. As a result, FIGS.
Can be adjusted.

FIGS. 4 to 8 show adjustment examples when the theoretical luminance range of the video signal is set to 0 to 1 V. FIG. 4A shows the state of AD conversion, and FIG. Is shown.

FIG. 4 shows an example in which the theoretical luminance range matches the actual luminance range, that is, the luminance distribution is averaged. Since the luminance of any level exists in one screen on average, the threshold value of the AD conversion is not adjusted. Therefore, the normal gradation display range corresponding to the theoretical luminance range is set. You.

FIG. 5 shows an example in which 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 only about half of the eight gradations are used if the standard specifications of FIG. Therefore, in this example, when such a luminance distribution is detected by the luminance distribution detecting unit, the resistor R1 shown in FIG.
Is controlled so that the resistance values of the resistors R2 to R8 are low and the resistance values of the other resistors R2 to R8 are low, thereby changing the threshold value of the AD conversion and narrowing the gradation display range toward the lower level. . As a result, for example, all eight gradations are used within the gradation display range of 0 to 0.6 V, and the image quality is maintained.

At this time, if the highest luminance level becomes the same as the white level, the luminance level (0.6 V), which is in the middle in FIG. 4, becomes equal to the white level (1 V), and the abnormal level is obtained. The screen becomes brighter and does not match other scenes. Therefore, adjustment is performed by the pulse number changing unit that receives data from the luminance distribution detecting unit, and the number of light emitting pulses in each subfield is reduced to shorten the light emitting period and control so as to lower the overall higher luminance. Is done.

FIG. 6 shows an example in which the luminance distribution is biased toward the white level. This is a scene taken of the sky 1
When such a luminance distribution is detected by the luminance distribution detecting section in a scene where the screen is entirely bright, the resistance value of the resistor R8 in FIG. 3 is large, and the resistance values of the other resistors R1 to R7 are small. By performing such control, the threshold value of the AD conversion is changed, and adjustment is performed to narrow the gradation display range toward a higher level.
As a result, for example, within the gradation display range of 0.4 to 1 V, 8
All gradations will be used and image quality will be maintained.

At this time, if the lowest luminance level becomes the same as the black level, the luminance level (0.4 V), which is in the middle in FIG. 4, becomes equal to the black level (0 V). The screen darkens and no longer matches the other scenes. Therefore, the adjustment is performed by the pulse number changing unit that receives the data from the luminance distribution detecting unit. By increasing the number of light emitting pulses in each subfield, the light emitting period is lengthened, and control is performed so as to increase the lower luminance as a whole. Is done.

FIG. 7 shows an example in which the luminance distribution is concentrated in the middle between the black level and the white level. This is a scene in which there is no bright or dark pole in one screen. When such a luminance distribution is detected by the luminance distribution detection unit, the resistors R1 and R1 in FIG.
By controlling the resistance value of R8 to be large and the resistance values of the other resistors R2 to R7 to be small, the threshold value of the AD conversion is changed, and adjustment for narrowing the gradation display range to an intermediate level is performed. As a result, for example, all eight gradations are used within the gradation display range of 0.2 to 0.8 V, and the image quality is maintained.

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, bright portions on the screen are significantly brighter, and dark portions are significantly darker. Unusual differences in light and darkness make it unmatched with other scenes. Therefore, the adjustment is performed by the pulse number changing unit that receives the data from the luminance distribution detecting unit, and light is emitted in the lower subfield from the lowest luminance level (0.2 V) to the central luminance level (0.5 V) of the distribution. While increasing the number of pulses, the center luminance level (0.5
V) to the highest luminance level (0.8 V) is controlled so as to reduce the number of light emission pulses (the center luminance level is not controlled by the number of light emission pulses). As a result, the brightness approaches the luminance at the distribution center as a whole, so that an abnormal brightness difference is prevented.

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 in which there is an extreme brightness difference in one screen. When such a brightness distribution is detected by the brightness distribution detecting unit, the resistance R4 in FIG.
The resistance value of R5 is large, and the other resistors R1 to R3, R6 to
By controlling the resistance value of R8 to be small, AD
The threshold value of the conversion is changed, the gradation display range is narrowed toward the bipolar level, and the adjustment is performed with a middle level. As a result, for example, in both gradation display ranges of 0 to 0.3 V and 0.7 to 1 V, 4
All eight gradations are used for each gradation, and the image quality is maintained. At this time, there is no need to change the number of light emission pulses.

[0025]

According to the present invention, an optimum gradation display range is set according to the luminance distribution of the display screen, and it is possible to use as many gradations as possible within the actual luminance range. Even in a dark scene or an extremely bright scene, black and white are not lost, and the image quality can be improved as a whole. If the number of light emission pulses is not controlled in the case described with reference to FIG.
Since it is possible to intentionally brighten a dark scene for viewing, convenient applications such as brightening and watching a nighttime image so that it can be easily understood are also possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a driving method of a conventional plasma display device.

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 converter in FIG. 2;

FIG. 4 shows A when the theoretical luminance range and the actual luminance range match.
FIG. 4 is an explanatory diagram showing D conversion.

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 at an intermediate level between the black level and the white level.

FIG. 8 is an explanatory diagram showing AD conversion when the actual luminance range is biased to both the black level and the white level.

Claims (6)

[Claims] 1. An AD conversion method for an analog video signal, wherein the AD conversion threshold is changed in accordance with a predetermined operation when the analog video signal is converted into a digital signal. 2. The method according to claim 1, wherein a luminance distribution in the analog video signal to be converted is detected and a threshold value of the AD conversion is changed in accordance with the luminance distribution in the AD conversion in which the analog video signal is converted into a digital signal. A / D conversion method for an analog video signal. 3. A method of driving a plasma display apparatus, in which one frame is composed of a plurality of subfields having different relative ratios of luminance and which performs multi-gradation display, performs a predetermined operation when performing an AD conversion that converts an analog video signal into a digital signal. A driving method characterized in that a threshold value of the AD conversion is changed according to the following. 4. A driving method for a plasma display device which constitutes one frame from a plurality of subfields having different relative ratios of luminance and performs multi-gradation display, in an AD conversion in which an analog video signal is a digital signal, A driving method wherein a luminance distribution in an analog video signal is detected, and a threshold value of AD conversion is changed in accordance with the luminance distribution. 5. The driving method according to claim 4, wherein when the highest luminance level of the detected luminance distribution is lower than the white level, the number of light emission pulses in a predetermined subfield is reduced. 6. The driving method according to claim 4, wherein when the lowest luminance level of the detected luminance distribution is higher than the black level, the number of light emission pulses in a predetermined subfield is increased.