JP3344521B2 - A / D converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D converter for converting an analog video signal into a digital signal.

[0002]

2. Description of the Related Art Conventionally, the input of an analog video signal is converted into a digital signal using A / D conversion. However, when a video signal is input at a level around a threshold value, a conversion error occurs. This is likely to occur, and even with a constant input analog signal, the value of the digital signal output may change, and these appear as noise on the display screen, deteriorating the image quality.

[0003]

In the conventional method, A /
When converting into a digital signal by D conversion, conversion errors may occur, which appear as noise on the display screen, deteriorating the image quality. The present invention detects whether an input video signal is lower than the resolution of an A / D converter, and corrects and outputs a converted digital signal if a video signal input having a resolution lower than the resolution has discrete characteristics. Accordingly, an object of the present invention is to provide an A / D converter capable of reducing noise such as a conversion error and obtaining good image quality.

[0004]

Means for Solving the Problems The first invention of the present application is an RG
Signal conversion means for converting a video signal input of a B signal into a digital signal, each gradation detection means for detecting a distribution of each gradation from the digital signal, and a signal generated when the signal conversion means converts the signal into a digital signal. Correction means for correcting the conversion error to be performed, for each of the RGB signals, a discrimination means for discriminating between a discrete gradation and a random gradation from the detection signal of each gradation detection means, and a discrimination by this discrimination means A control unit that controls a correction coefficient of the correction unit based on a result and a detection signal of each of the gradation detection units. The second invention of the present application is directed to a second aspect of the present invention, wherein each of the tone detection means detects a predetermined number of codes of the digital signal, and each of the code detection sections is connected to each of the code detection sections. It is characterized by comprising a counter for counting the number of occurrences, and a selector for sequentially switching and outputting the count number input from the counter.

According to a third aspect of the present invention, there is provided a field memory in which the correcting means delays the digital signal converted by the signal converting means by one field and outputs the digital signal, and a memory provided with a conversion table for correcting the output from the field memory. Wherein the conversion coefficient of the conversion table is rewritten by a control signal from the control unit to correct the digital signal. According to a fourth aspect of the present invention, the discriminating unit compares the calculated difference value with a calculation unit that calculates a difference value between the gradations of adjacent peaks with respect to a detection signal input from each gradation detection unit. And a determining unit for determining whether the tone is discrete. In the fifth invention of the present application, when the discriminating means determines that the tone is a discrete tone, the control unit discriminates a tone deviating from the discrete tone from the detection signal of each tone detecting means, It is characterized in that a control signal for rewriting the conversion coefficient of the conversion table is output, and rounding processing is performed so that a tone deviating from the discrete tone falls into a nearby peak tone.

[0006]

In the A / D converter of the first invention of the present application,
Signal conversion means for converting each primary color signal of a video signal input as an RGB signal into a digital signal; each gradation detection means for detecting a distribution of each gradation from the converted digital signal; Correction means for correcting a conversion error generated when converting into a digital signal, wherein the detection signals from the respective gradation detection means are respectively inputted to the discrimination means, and the detection signals are inputted from the discrimination means. The control unit controls the correction coefficient of the correction unit by determining whether the gradation is a discrete gradation or a random gradation. When the gradation is a discrete gradation, the gradation is discrete from the detection signal from each of the gradation detection units. To correct the gradation signal that deviates from
When the gradation is random, the same gradation code is used to output, so that noise such as a conversion error can be reduced.

In an A / D converter according to a second aspect of the present invention, in the first aspect, each gradation detecting means detects each code of a number corresponding to the number of bits of the digital signal converted by the signal converting means. A code detecting unit, a counter connected to each of the code detecting units for counting the number of occurrences of the same code detected by the code detecting unit, and a selector for sequentially switching and outputting the count number input from the counter And therefore,
It is possible to detect the distribution of each gradation of the digital signal. In an A / D converter according to a third aspect of the present invention, in the first aspect of the invention, the correcting means delays the digital signal converted by the signal converting means by one field and outputs the field signal, and the output from the field memory. And a memory provided with a conversion table for correcting the conversion coefficient, and the conversion coefficient of the conversion table is rewritten by a control signal from the control unit. Therefore, noise such as a conversion error is corrected by the rewritten conversion table. Output can be performed, so that noise can be reduced.

In the A / D converter according to a fourth aspect of the present invention, in the first aspect, the discriminating means may be configured such that the detection signal input from each of the gradation detecting means is used to determine whether the gradations of adjacent peaks correspond to each other. And a discriminator for comparing the calculated difference value to determine whether the gradation is a discrete gradation. When the video signal input is a gradation that is less than the resolution of the signal conversion means, If there is, the difference value calculated by the calculation unit is constant, and if it is a random gradation, the difference value is not constant, so it is possible to determine whether the gradation is discrete or random. Becomes In the A / D converter according to the fifth aspect of the present invention, in the first to fourth aspects, when the discriminating means determines that the tone is discrete, the control section detects the detection signal of each tone detecting means. From the discrete gradations, and rewrite the conversion coefficient in the conversion table to round the gradations indicating noise such as a conversion error out of the discrete gradations to the nearest peak gradation. Processing is performed, so that noise can be reduced.

[0009]

FIG. 1 is a block diagram showing an embodiment of an A / D converter according to the present invention. RGB for video signal input
Signals, and among them, the R signal is input to the input terminal 11,
The G signal is input to the input terminal 21 and the B signal is input to the input terminal 31.
Is being entered. R signal converter 12, G signal converter 22
And the B signal converter 32 have the same configuration, the R signal is input to the R signal converter 12 via the input terminal 11, the G signal is input to the G signal converter 22 via the input terminal 21, and the B signal is The signal is input to the B signal converter 32 via the input terminal 31. The R signal conversion unit 12 includes an A / D converter 1 for converting an input R signal into a digital signal, and a gradation detection unit 2 for detecting a distribution of each gradation from the converted digital signal.
And a selector 3 for correcting a conversion error or the like of a converted digital signal, and a correction means including a field memory 4 and a memory 5 provided with a conversion table. ing.

FIG. 2 is a block diagram showing the configuration of each tone detector 2 of FIG. Assuming that the digital signal is converted into an 8-bit digital signal by the A / D converter 1, the code detectors 100 to 1FF for detecting each code of 256 gradations are connected to the code detectors 100 to 1FF. Each gradation detection unit 2 is composed of counters 200 to 2FF that count the number of occurrences of a part, and the counters 200 to 2FF count the number of occurrences of the same code in one field, and the count number is sequentially switched by a selector 3 and output. I do.

FIG. 3 is an explanatory diagram showing an example of a detection signal of each gradation detector 2 in FIG. In the figure, the horizontal axis represents each code (gradation) detected by each of the code detection units 100 to 1FF.
And the vertical axis indicates the count result of the number of occurrences in each of the counters 200 to 2FF. If the R signal input to the input terminal 11 is lower than the resolution of the A / D converter 1, for example, 64
When the signal is a gray scale signal, a peak frequently occurs every four steps as shown in the figure, and when the input R signal is a signal of 32 gray scales, the peak frequently occurs every eight steps. A peak occurs. When a conversion error occurs in the A / D converter 1 or when a signal input to the A / D converter 1 includes noise, for example, d3, d4, and d5
As shown in the figure, the peaks (d1 and d2
Etc.) are generated.

FIG. 4 is a flowchart showing a control procedure of the microcomputer 6. Hereinafter, an embodiment will be described with reference to FIG. For example, a microcomputer is used as the control unit 6,
The control program is stored in the ROM 7 in advance, and the control unit 6 reads out the control program stored in the ROM 7 and controls each unit. First, in step S1, the input terminal 1
A vertical synchronizing signal (VD) synchronized with the video signal input via the interface 1 is fetched, and in step S2, a detection signal of each gradation shown in FIG. 3 is fetched from the selector 3 and transferred to the RAM 8 for storage. The detection signal detected by the selector 3 is
The discriminating means for discriminating between a discrete gradation and a random gradation is composed of a computing unit 9 and a discriminating unit 10.
Then, the data stored in the RAM 8 is read out, and the arithmetic unit 9 calculates a difference value by subtracting adjacent peaks of the number of occurrences, and proceeds to step S4. Step S4
, The calculation result of the calculation unit 9 is input to the determination unit 10, and the determination unit 10 compares the difference values. In step S5, it is determined whether the comparison result has regularity.

In the example shown in FIG. 3, since the comparison result between the difference values is four steps, the A / D converter 1 can determine that the signal is a signal of a discrete gradation.
The video signal input can be determined to be a video signal input such as a random moving image or a video signal input exceeding the resolution of the A / D converter 1. On the other hand, the digital signal from the A / D converter 1 is input to the field memory 4, delayed by one field in the field memory 4, output and input to the memory 5, and the input is converted by the conversion table provided in the memory 5. The output can be corrected. If it is determined in step S5 that there is no regularity as a result of the comparison, the process proceeds to step S7, and the control unit 6 determines in step S7.
, The signal conversion in the conversion table in the memory 5 is stopped by the control signal input from the memory 5, and the input gradation is output as it is, and the processing is terminated.

If it is determined in step S5 that there is regularity, the process proceeds to step S6, and in step S6,
The data of the gradation distribution shown in FIG. 3 stored in the RAM 8 is read out, and a control signal input from the control unit 6 causes a gradation signal deviating from discrete gradations, for example, a gradation signal of d3, d4 and d5. The conversion coefficient in the conversion table of the memory 5 for correcting the d is rewritten so that d3 (gradation 53) and d4 (gradation 5
5) is converted so as to fall within the near peak gradation, d1 (54 gradation), and d5 (gradation 57) is similarly transformed into the nearby peak gradation, d2 (58 gradation). to correct.
By rewriting the conversion coefficient of the conversion table, a rounding process can be performed so that a tone indicating a noise such as a conversion error deviating from a discrete tone falls within a nearby peak tone, and thus noise such as a conversion error can be reduced. Since correction can be performed, noise can be reduced.

Although the circuit operation of the R signal conversion unit 12 has been mainly described above, the G signal conversion unit 22 and the B signal conversion unit 32 have the same configuration as the R signal conversion unit 12. Since noise such as a conversion error can be corrected and output for the B signal as well, noise can be reduced. For example, when a signal such as a moving image is input as a video signal input, the signal conversion in the conversion table is stopped, and the input gradation is output as it is so that the image quality is not impaired. Is detected, whether the resolution is lower than the resolution of the A / D converter 1 is detected.
Since noise such as a conversion error is corrected and output, good image quality with less noise can be obtained.

[0016]

As described above, according to the present invention,
Each gradation detecting means detects the distribution of each gradation, and the discriminating means detects whether or not the video signal input is lower than the resolution of the A / D converter. And an A / D converter capable of correcting the converted digital signal and outputting the corrected digital signal. Therefore, it is possible to provide an A / D converter capable of reducing noise such as a conversion error and obtaining good image quality. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an A / D converter according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of each gradation detection unit in FIG. 1;

FIG. 3 is an explanatory diagram illustrating an example of a detection signal of each gradation detection unit in FIG. 1;

FIG. 4 is a flowchart illustrating a control procedure of a control unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 Each gradation detection part 3 Selector 4 Field memory 5 Memory 6 Control part 7 ROM 8 RAM 9 Operation part 10 Discrimination part 11 Input terminal 12 R signal conversion part 21 Input terminal 22 G signal conversion part 31 Input terminal 32 B signal conversion unit 100 Code detection unit 200 Counter

Claims (5)

(57) [Claims] 1. A signal conversion means for converting a video signal input of an RGB signal into a digital signal, each gradation detection means for detecting a distribution of each gradation from the digital signal,
A correction means for correcting a conversion error generated when converting to a digital signal by the signal conversion means, for each of the RGB signals, wherein a discrete or random gradation is detected from a detection signal of each of the gradation detection means. An A / D conversion device comprising: a determination unit for determining whether the correction is performed; and a control unit that controls a correction coefficient of the correction unit based on a determination result of the determination unit and a detection signal of each of the gradation detection units. . 2. A method according to claim 1, wherein each of said tone detecting means detects each code of the digital signal, and said code detecting section is connected to each of said code detecting sections, and the number of occurrences of the same code detected by said code detecting section. 2. The A / A converter according to claim 1, further comprising: a counter for counting each of the count values; and a selector for sequentially switching and outputting the count number input from the counter.
D conversion device. 3. A field memory in which the correction means delays the digital signal converted by the signal conversion means by one field and outputs the data, and a memory provided with a conversion table for correcting the output from the field memory. 2. The A / D converter according to claim 1, wherein the conversion coefficient of the conversion table is rewritten by a control signal from a control unit to correct the digital signal. 4. An arithmetic unit for calculating a difference between adjacent peak gray scales with respect to a detection signal input from each of the gray scale detecting units, and a gray scale obtained by comparing the calculated difference values with each other. 2. The A / D converter according to claim 1, further comprising a determination unit that determines whether the gradation is a random gradation. 5. When the discriminating means determines that the tone is a discrete tone, the control unit discriminates a tone deviating from the discrete tone from the detection signal of each tone detecting means, And outputting a control signal for rewriting the conversion coefficient of (1), and performing rounding processing so that a tone deviating from the discrete tone falls into a nearby peak tone. The A / D converter according to claim 3 or 4.