JP4474737B2 - Tone correction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradation reduction technique in a display device using a digital drive display device such as a liquid crystal display or a plasma display.
[0002]
[Prior art]
Conventionally, a video signal output from a personal computer (hereinafter referred to as a PC) is generally a high gradation analog signal, whereas a digitally driven display with a small number of output gradations typified by an STN liquid crystal display. In the apparatus, the input analog video signal is converted into a digital signal (hereinafter referred to as A / D conversion), and then the gradation is reduced and output to the display device.
[0003]
In such a display device having A / D conversion, weak fluctuations and jitter noise of an analog signal are quantized by A / D conversion and are displayed on the screen as noise of one gradation amplitude (denoted as quantization noise). It is output and becomes a problem.
[0004]
Such a problem will be described with reference to FIG. FIG. 8 shows a state in which a video signal with an analog luminance level of 0.2V is A / D converted with a threshold value in increments of 0.1V, and the change in the video signal is sufficiently smaller than the step size of the threshold. Depending on the sampling timings 1F, 2F, and 3F, the converted data outputs values that fluctuate as “1”, “2”, and “1”, and this is output as noise.
[0005]
In order to solve such a problem, as shown in FIG. 9 in Japanese Patent Laid-Open No. 5-284425, two threshold value storage means (threshold value group 1, threshold value group 2) are selected according to the analog input level. ) To achieve a stable A / D conversion output and reduce quantization noise. In the case of the signal in FIG. 8, quantization noise is not generated by using the threshold value group 2.
[0006]
[Problems to be solved by the invention]
However, the quantization noise reduction method described above has to prepare threshold groups for each gradation of A / D conversion in advance, and cannot cope with various video signals in detail. was there.
[0007]
Further, in the above-described conventional low gradation display device, there is an inevitable problem that a luminance difference between input video signals is lost due to gradation reduction.
[0008]
[Means for Solving the Problems]
Therefore, in the gradation correction apparatus of the present invention, focusing on the fact that the quantization noise holds the amplitude of one gradation and exists on the luminance distribution together with the video data, the luminance distribution of the digital signal after A / D conversion is detected. Thus, the quantization noise output to the screen is reduced by positioning the gradation reduction threshold value in the luminance region where the video data is small (and hence the quantization noise is low), that is, in the valley of the luminance distribution. .
[0009]
In addition, by dividing the luminance distribution of the video signal input to the gradation reduction circuit equally into each gradation data output from the gradation reduction circuit, the limited number of output gradations can be used effectively, and the contrast feeling can be effectively utilized. It is intended to realize an image display with
[0010]
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the present invention, in the display device that performs analog-to-digital conversion of an analog video signal to a high-gradation digital video signal and then outputs the result to a low-gradation display device after reducing the gradation. A gradation correction apparatus, wherein the amplitude and black level of the analog signal are set so that a threshold for gradation reduction is positioned in a trough of a luminance distribution of a tone digital video signal. The generated quantization noise is reduced when the gradation is reduced, and a screen display with less noise is realized.
[0011]
According to a second aspect of the present invention, there is provided a video amplifier for adjusting the amplitude and black level of an analog video signal, an A / D converter for converting the output of the video amplifier into a high-gradation digital video signal, and the A luminance distribution detection circuit for detecting a luminance distribution of a high gradation digital video signal, a gradation reduction circuit for reducing the gradation of the high gradation digital video signal to the number of gradations of a display device, and a threshold of the gradation reduction circuit Is a gradation correction device composed of a microcontroller that controls the video amplifier so as to be located in the valley of the luminance distribution, and reduces quantization noise generated by A / D conversion at the time of gradation reduction, resulting in less noise It is what realizes the screen display.
[0012]
According to a third aspect of the present invention, there is provided a display device that performs analog-to-digital conversion of an analog video signal into a high-gradation digital video signal and then reduces the gradation and outputs it to a low-gradation display device. A gradation correction apparatus, characterized in that the threshold value is set so that the threshold value for gradation reduction is located in the valley of the luminance distribution of the digital video signal, and quantization generated by A / D conversion Noise is reduced at the time of gradation reduction, and a screen display with less noise is realized.
[0013]
According to a fourth aspect of the present invention, there is provided an A / D converter that converts an analog video signal into a high gradation digital video signal, a luminance distribution detection circuit that detects a luminance distribution of the high gradation digital video signal, and the Consists of a gradation reduction circuit that reduces the gradation of a high gradation digital video signal to the number of gradations of the display device by a variable threshold and a microcontroller that sets the threshold of the gradation reduction circuit in the valley of the luminance distribution This is a gradation correction device that reduces quantization noise generated by A / D conversion when reducing gradation and realizes screen display with less noise.
[0014]
According to a fifth aspect of the present invention, in a display device that outputs a high gradation digital video signal to a low gradation display device by reducing the gradation, each luminance distribution of the digital video signal after gradation reduction is provided. The gradation correction apparatus is characterized in that the threshold value for gradation reduction is set so that the frequency is equalized, and the frequency distribution of the luminance distribution of the video data after gradation reduction is almost uniform. The number of output tones is effectively utilized, and an image display with a sense of contrast is realized.
[0015]
According to a sixth aspect of the present invention, there is provided a luminance distribution detection circuit for detecting a luminance distribution of a high gradation digital video signal, and the gradation of the high gradation digital video signal according to a variable threshold. A gradation composed of a gradation reduction circuit for gradation reduction and a microcontroller for setting a threshold value of the gradation reduction circuit so that each frequency of the luminance distribution of the digital video signal output from the gradation reduction circuit is equal. It is a correction device, and each frequency of the luminance distribution of the video data after gradation reduction is almost uniform, so that the output gradation number of the display device is effectively used and an image display with a sense of contrast is realized. .
[0016]
Hereinafter, an example of an embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.
[0017]
(Embodiment 1)
FIG. 1 is a block structure diagram of a gradation correction apparatus according to Embodiment 1 of the present invention.
[0018]
In FIG. 1, reference numeral 101 denotes a video amplifier that adjusts the amplitude and black level of an analog video signal, and reference numeral 102 denotes an A / D that performs A / D conversion of the analog video signal output from the video amplifier 101 into an M-gradation digital video signal. A converter 103 is a luminance distribution detection circuit for detecting the luminance distribution of the M gradation digital video signal output from the A / D converter 102, and 104 is an N gradation (M> N) a gradation reduction circuit for reducing gradation in the digital video signal, and 105 controls the gradation reduction threshold of the gradation reduction circuit 104 and the video amplifier 101 based on the detection result of the luminance distribution detection circuit 103. Then, the microcontroller adjusts the black level and amplitude of the analog video signal input to the A / D converter 102.
[0019]
As an example of this embodiment, FIG. 2 shows an internal configuration example of the gradation reduction circuit 104 when the number of gradations in FIG. 1 is M = 16 and N = 4.
[0020]
2A is a diagram showing the block configuration of 104. In FIG. 2A, reference numerals 401, 402, and 403 denote input 4-bit video data, threshold value TH1, threshold value TH2, and threshold value TH3 ( TH1 <TH2 <TH3), and a comparator that outputs 1 if the video data is equal to or greater than the threshold value, and 0 if the video data is less than the threshold. 404 is a comparator 401, comparator 402, and 2B is a decoder that outputs the values shown in FIG. 2B from the output, and 405 is a register that holds threshold values TH1, TH2, and TH3 set by the microcontroller 105 (FIG. 1). .
[0021]
Further, FIG. 3 shows a detection result of the luminance distribution detection circuit 103 when a specific video signal is inputted, and a gradation reduction circuit when the threshold values TH1, TH2, and TH3 are set at equal intervals. FIG. 3 shows a correspondence relationship between the output data of 104, and in FIG. 3, since there is a large amount of luminance data and quantization noise before and after the threshold values TH2 and TH3, the output data of the gradation reduction circuit 104 is displayed. In addition, values in which “1” and “2” and “2” and “3” fluctuate are output and recognized as noise on the display screen.
[0022]
FIG. 4 shows how the microcontroller 105 increases the black level of the video amplifier 101 by one gradation of the output of the A / D converter 102 with such a configuration. In FIG. 4, since there is no video data before or after the threshold value TH1 and threshold value TH2, there is no quantization noise, and the video data before and after the threshold value TH3 is also less than in the case of FIG. The quantization noise of the output data of the gradation reduction circuit is also reduced as compared with the case of FIG.
[0023]
As described above, according to the present embodiment, it is possible to eliminate quantization noise at the time of gradation reduction even when a gradation reduction circuit that cannot variably set the threshold value is used.
[0024]
Further, although the black level is adjusted in this embodiment, the threshold can be positioned more finely in the valley of the luminance distribution by adding the amplitude adjustment, so that it is possible to effectively reduce noise.
[0025]
(Embodiment 2)
Next, another embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG. Note that the same constituent elements as those of the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted.
[0026]
FIG. 1 is a block diagram showing the structure of a gradation correction apparatus according to this embodiment of the present invention. The block diagram is the same as the structure of the gradation correction apparatus described in (Embodiment 1). .
[0027]
With such a configuration, in FIG. 5, the threshold TH1 is left as it is from the state shown in FIG. 3, and the threshold TH2 and the threshold TH3 are increased in luminance by one gradation of the output of the A / D converter 102. In this figure, there is no image data before or after the threshold value TH1, threshold value TH2, or threshold value TH3, so there is no quantization noise. No noise is output. In other words, all the quantization noise can be eliminated by the gradation reduction circuit.
[0028]
Therefore, each threshold value can be freely set in the gradation correction apparatus according to the present embodiment, so that it is more effective than the example of the gradation correction apparatus described in the above (Embodiment 1). Noise can be reduced.
[0029]
(Embodiment 3)
Next, another embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, FIG. Note that the same constituent elements as those of the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted.
[0030]
FIG. 1 is a block diagram showing the structure of a gradation correction apparatus according to an embodiment of the present invention. The block diagram is the same as that described in (Embodiment 1) and (Embodiment 2). is there.
[0031]
With this configuration, FIG. 6 shows that the threshold TH3 is left unchanged from the state shown in FIG. 3 so that the frequencies of the luminance distribution of the digital video signal after gradation reduction are equal, and the threshold TH1 is set to two gradations. And the threshold value TH2 is set to a brightness higher by one gradation.
[0032]
7A shows the output luminance distribution of the gradation reduction circuit 104 according to the threshold shown in FIG. 3, and FIG. 7B shows the output luminance distribution of the gradation reduction circuit 104 according to the threshold shown in FIG. Represents the output luminance distribution. In FIG. 7A, most of the luminance data exists in 3 gradations, whereas in FIG. 7B, the output data exists almost uniformly in all 4 output gradations. It is possible to output an image with a sense of contrast using all of the tone.
[0033]
【The invention's effect】
As described above, according to the gradation correction apparatus of the present invention, it is possible to reduce the quantization noise generated by A / D conversion during gradation reduction and realize a screen display with less noise.
[0034]
In addition, it is possible to realize an image display with a sense of contrast by effectively utilizing the number of output gradations of the display device.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a gradation correction apparatus according to the present invention. FIG. 2 is a block diagram showing a configuration of a gradation reduction circuit of the gradation correction apparatus. FIG. 4 is a diagram showing a previous luminance distribution. FIG. 4 is a diagram showing a first example of a luminance distribution after gradation reduction of the gradation correction device. FIG. FIG. 6 is a diagram showing a third example of luminance distribution after gradation reduction of the gradation correction device. FIG. 7 is an output luminance from a gradation reduction circuit of the gradation correction device. Fig. 8 is a diagram showing an example of distribution. Fig. 8 is a diagram showing the cause of quantization noise. Fig. 9 is a block diagram of conventional quantization noise suppression technology.
101 Video Amplifier 102 A / D Converter 103 Luminance Distribution Detection Circuit 104 Gradation Reduction Circuit 105 Microcontroller 301 Threshold Storage Unit 1
302 Threshold storage unit 2
303 Switcher 304 A / D Converter 401, 402, 403 Comparator 404 Decoder 405 for Outputting Gradation Reduction Data from Comparator Result Register for Holding Threshold for Gradation Reduction

Claims (1)

An A / D converter that converts an analog video signal into a digital video signal;
A luminance distribution detection circuit for detecting a luminance distribution of the digital video signal;
A gradation reduction circuit that holds a plurality of thresholds for reducing the number of gradations of the digital video signal;
A microcontroller for individually controlling the plurality of threshold values so as to be located in valleys of the luminance distribution;
A gradation correction circuit comprising:

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