JP3385705B2 - Gradation correction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver,
The present invention relates to a gradation correction device used for correcting a gradation of a video signal, such as a video tape recorder, a video camera, and a video disk. 2. Description of the Related Art In recent years, as a color television receiver has become larger and has higher image quality, a tone correction device has been developed by passing a video signal through a non-linear amplifier in order to make an image look sharper. It has been regarded as important for correcting the gradation of a video signal and expanding the dynamic range of a video on a CRT. [0003] A conventional tone correction device will be described below. FIG. 2 shows a block diagram of a conventional tone correction device. In FIG. 2, reference numeral 1 denotes an AD converter for converting an input luminance signal into a digital value. Reference numeral 2 denotes a histogram memory for extracting a luminance histogram of the input luminance signal. Generally, a luminance level of the input signal is stored in an address of the memory, and a frequency is included in the data. Reference numeral 3 denotes a histogram operation circuit which calculates an average value, a mode value, a minimum value, a maximum value,
A deviation coefficient, a white area, a black area, and the like are calculated. Based on the calculation results, control values such as a limiter level, a constant addition value, an accumulated start luminance level, an accumulated stop luminance level, and a maximum luminance level are calculated. , Accumulation control register circuit 5, normalization control register circuit 6
Output to Reference numeral 4 denotes a limiter / addition circuit that processes data in the histogram memory 2. That is, the control data transferred from the histogram calculation circuit 3 restricts the frequency of the luminance histogram so that the frequency does not exceed a certain level, or performs an addition calculation of a constant value. Generally, during the period of extracting the luminance histogram (the period of sampling), the data processing ends while the address is accessed once. Reference numeral 5 denotes an accumulation control register circuit, which is supplied with a luminance level at which accumulation is to be started and a luminance level at which accumulation is to be stopped from the histogram operation circuit 3 to obtain an accumulation histogram, and controls the histogram accumulation and addition circuit 7. Reference numeral 6 denotes a normalization control register circuit. When a lookup table is created by normalizing the data of the cumulative histogram, the maximum luminance level of the output luminance signal after the normalization is given from the histogram operation circuit 3. The normalization coefficient used in the lookup table calculation circuit 9 is controlled according to the value of the maximum luminance level so that the maximum cumulative frequency of the cumulative histogram becomes the maximum luminance level. Reference numeral 7 denotes a histogram accumulative addition circuit, which accumulates processing data of the histogram memory 2 according to a control signal of the accumulative control register circuit 5. Reference numeral 8 denotes a cumulative histogram memory, which stores the result of the cumulative operation of the histogram cumulative adding circuit 7. In general, the luminance level is set in the address of the memory, and the frequency is set in the data. Reference numeral 9 denotes a look-up table operation circuit, which normalizes each data of the cumulative histogram memory 8 based on the output signal of the normalization control register circuit 6, and then subtracts the corresponding luminance level from each data to obtain each luminance level. Is calculated. [0005] Reference numeral 10 denotes a look-up table, which stores correction data calculated by the look-up table operation circuit 9. In general, the luminance level is set in the address of the memory and the correction data is set in the data. A timing control circuit 11 controls the order of each operation, controls each memory, and the like. Reference numeral 12 denotes a luminance correction operation circuit, which performs a gradation correction operation by using a luminance signal of each pixel as an address, a correction signal read from a lookup table and a video signal as inputs. Reference numeral 13 denotes a DA converter, which converts a digital signal output from the luminance correction operation circuit 12 into an analog signal. Reference numeral 15 denotes an AD converter for converting an input color signal into a digital value. Reference numeral 16 denotes a color correction operation circuit,
In order to keep the / C ratio constant before and after the gradation correction, a color signal obtained by multiplying the gradation correction data used in the luminance correction operation circuit 12 by C / Y by the luminance level and color level of the corresponding pixel. A / D converter 15 using the gradation correction data of
A gradation correction operation is performed on the color signal output from. 17 is DA
The converter converts a digital signal output from the color correction operation circuit 16 into an analog signal. [0007] The operation of the gradation correction circuit configured as described above will be described below. FIG. 3 shows the operation of each unit. First, the input luminance signal a is input to the AD converter 1, converted into a digital signal, and output as a converted input luminance signal b. The histogram memory 2 uses the converted input luminance signal b as an address, and adds 1 to the data at the address for each data. By performing this operation for one vertical scanning period, a luminance histogram of the input luminance signal a can be extracted. This state is shown in FIG. Next, the data in the histogram memory 2 containing the luminance histogram is read out by the histogram calculation circuit 3, and the average value, mode value, minimum value, maximum value, deviation coefficient, white area, black area of the input luminance signal a are obtained. Calculate etc.
From these calculation results, control values such as a limiter level, a fixed addition value, a start brightness level and a stop brightness level for cumulative calculation, and a maximum brightness level after normalization are obtained, and these control signals e are converted to a limiter / addition circuit. 4. Transfer to the accumulation control register circuit 5 and the normalization control register circuit 6. Next, a limiter / adder 4 reads data from the histogram memory 2 and applies a limiter (see FIG. 3B) or a constant to each data based on each control signal transferred from the histogram arithmetic circuit 3. Addition of values (Fig. 3
(See (c)), and outputs the result to the histogram accumulation circuit 7 as corrected histogram data c. Here, the larger the constant value to be added, the closer the cumulatively added curve is to a straight line, and the smaller the value, the closer to the histogram flattening process (see FIG. 3D). The histogram accumulative adding circuit 7
Based on the cumulative start luminance level and the cumulative stop luminance level given from the cumulative control register circuit 5, the cumulative histogram data f of the corrected histogram data c is calculated within the range, and the result is stored in the cumulative histogram memory 8. This situation is shown in FIGS. 3C and 3D. Next, look-up table operation circuit 9
Reads data from the cumulative histogram memory 8,
A normalization coefficient is determined so that the maximum value of the cumulative histogram data becomes the maximum output luminance level h given from the normalization control register circuit 6. Based on this coefficient, normalization processing is performed on each data g of the cumulative histogram. Is performed, the corresponding luminance level is subtracted from each data, and the result i is stored in the look-up table 10. At this time, by controlling the maximum output luminance level h, automatic contrast control (ACL) or automatic bright control (AB) is performed.
Operation L) can be performed. This operation is shown in FIG. Next, the look-up table 10 reads the data j using the converted input luminance signal b as an address, and performs the gradation correction operation by the luminance correction operation circuit 12 using the data j and the converted input luminance signal b as inputs. , A corrected output luminance signal k is obtained. FIG. 3F shows a histogram of the corrected luminance signal. And 13 DA converters A
Converts the corrected output luminance signal k into an analog signal l and outputs it. The input color signal m is digitally converted by the AD converter 15 to obtain a converted input color signal n. Then, the conversion input color signal n is input to the color correction operation circuit 16 together with the luminance gradation correction data j and the conversion input luminance signal b, and the data j for the luminance correction is converted into the conversion input luminance signal b and the conversion input color signal n. Data for color correction is calculated by calculation (C / Y times). Further, a gradation correction operation of the converted input color signal n is performed by using the color correction data to obtain a corrected output color signal p. Then, the DA converter 17 outputs the corrected output color signal p
Is converted to an analog signal q and output. The timing control circuit 14 controls the operation of each circuit so that the operation of each unit is performed in the order described above. However, in the above-described conventional configuration, since the gradation correction data is obtained by using the look-up table of the luminance level of each pixel as an address, when the noise is superimposed on the luminance signal, it is difficult to obtain the gradation correction data. The obtained correction data is also affected by the correction data. For the color signal, the correction signal is C
Since the correction operation is performed using the data multiplied by / Y, the color signal after the correction is also affected by noise superimposed on the luminance signal. The present invention solves the above-mentioned problems. Generally, the color signal band is less than half the luminance signal band, and the general image data often has a two-dimensional correlation. And the color correction operation is performed at half the rate of the luminance correction operation, so that the color gradation correction data also has a half rate of the luminance gradation correction data. An object of the present invention is to provide a tone correction device that can reduce the influence of noise superimposed on a luminance signal on color tone correction by halving the average by taking C / Y times and then averaging the minutes. And In order to solve the above-mentioned problems, a gradation correction apparatus according to the present invention comprises: a first AD converter for converting an input luminance signal into a digital value; A histogram memory for storing a luminance histogram; and an AP of an input luminance signal based on data of the histogram memory.
Video features such as L value, maximum value, minimum value, etc. are extracted, and clip data, addition value, cumulative start value,
A histogram calculation circuit that calculates a control parameter such as an accumulated stop value; and a control data from the histogram calculation circuit that limits the maximum value of the data in the histogram memory, or adds a certain value to each data to add the data in the histogram memory. A limiter / adder circuit for processing, a histogram cumulative adder circuit for cumulatively adding the data of the histogram memory, a cumulative histogram memory for storing the calculation result, and the histogram cumulative adder circuit based on the control data obtained by the histogram calculator. A cumulative control register circuit for controlling the start and stop values of the histogram cumulative addition process, and a normalization process for the data of the cumulative histogram memory based on the maximum value of the cumulative histogram memory obtained by the histogram arithmetic circuit. And-normalized control register circuit,
A look-up table operation circuit for subtracting the corresponding luminance level from the data obtained after normalizing the data of the cumulative histogram memory under the control of the normalization control register circuit to calculate gradation correction data;
A look-up table for storing the calculation result, a luminance correction calculation circuit for performing gradation correction using a correction signal obtained from the look-up table using the same signal as the output signal of the first AD converter as an address; A first D / A converter for converting the subsequent video signal into an analog value, a second A / D converter for converting an input color signal into a digital value, and a luminance level of a pixel corresponding to the output correction signal of the look-up table. And an average value calculating circuit for calculating an average value of two pixels of the obtained data, and an output of the average value calculating circuit.
Power data and the output color signal of the second A / D converter.
And a color correction operation circuit for calculating the color correction data, and then performing the gradation correction, and a second DA converter for converting the calculated color signal into an analog value. According to the present invention, with the above-described structure, by obtaining gradation correction data in accordance with a luminance level for each pixel,
When performing gradation correction on the luminance and color signals, the calculation rate of the color gradation correction calculation is reduced compared to the luminance correction calculation,
By taking the average of two pixels of the luminance correction data of the corresponding pixels as the color gradation correction data and multiplying the data by C / Y, the influence of the noise superimposed on the luminance signal on the color gradation correction can be reduced. It is possible to realize gradation correction that can be reduced by half. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a tone correction device showing one embodiment of the present invention. In FIG. 1, the same parts as those in FIG. An average value calculation circuit 14 divides the gradation correction data used in the luminance correction operation circuit 12 by the luminance level of the corresponding pixel, and calculates 2
Take the average value of the data obtained in pixel units. 16 denotes a color correction operation circuit, and the output data of the average value calculating circuit 14
The color correction data is calculated by multiplying the color signal by a corresponding color signal, and a gradation correction operation is performed on the color signal output from the AD converter 15 using the correction data. The operation of the gradation correction circuit configured as described above will be described below. FIG. 3 shows the operation of each unit. As can be seen from the block diagram of FIG. 1, the operation of the gradation correction circuit for the luminance signal is the same as that of the conventional example. The difference from the conventional example is the operation of the gradation correction circuit for the color signal. That is, the luminance signal b of the pixel corresponding to the output signal j from the look-up table 10 is input to the average calculation circuit 14, and the luminance correction signal j is divided by the luminance signal b. And outputs correction data o. The input color signal m is digitally converted by the AD converter 15 to obtain a converted input color signal n. Then, the conversion input color signal n is input to the color correction operation circuit 16 together with the correction data o, and data for color correction is calculated by multiplying the correction data o by the conversion input color signal n. Further, a gradation correction operation of the converted input color signal n is performed by using the color correction data to obtain a corrected output color signal p. Then, the DA converter 17 converts the corrected output color signal p into an analog signal q and outputs the analog signal q. As described above, according to the present embodiment, it is possible to realize gradation correction that can reduce the influence of noise superimposed on a luminance signal on color gradation correction by half. As described above, according to the present invention, the second AD converter for converting an input color signal into a digital value and the output correction signal of the look-up table are divided by the luminance level of the corresponding pixel. And an average value calculation circuit for calculating an average value of two pixels of the obtained data, and an output color signal of the second AD converter and a tone correction signal of a pixel corresponding to the output color signal as inputs. By providing a color correction operation circuit for multiplying the two signals to obtain color correction data and thereafter performing gradation correction, and a DA converter B for converting the color signal after the calculation into an analog value, the color gradation correction is performed. And a halftone correction device capable of halving the influence of noise superimposed on the luminance signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a tone correction device showing one embodiment of the present invention. FIG. 2 is a block diagram of a conventional tone correction device. FIG. Histogram (b) Histogram of corrected luminance data when frequency is limited (c) Histogram of corrected luminance data when frequency is limited and a fixed value is added (d) Cumulative histogram of corrected luminance data (e) Output luminance level distribution diagram when the maximum output luminance level is controlled (f) Histogram of corrected luminance data after gradation correction operation [Description of Signs] 1 AD converter 2 Histogram memory 3 Histogram operation circuit 4 Limiter / addition circuit 5 Cumulative control register circuit 6 Normalization control register circuit 7 Histogram cumulative addition circuit 8 Cumulative histogram memory 9 Lookup Table arithmetic circuit 10 a look-up table 11 timing control circuit 12 the luminance correction operation circuit 13 DA converter 14 Average value calculating circuit 15 AD converter 16 color correction operation circuit 17 DA converter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/20, 9/68

Claims (1)

(57) A first AD converter for converting an input luminance signal into a digital value, a histogram memory for storing a luminance histogram of the input luminance signal, and data of the histogram memory A histogram calculation circuit for extracting video characteristics such as APL value, maximum value and minimum value of the input luminance signal and calculating control parameters such as a clip value, an addition value, a cumulative start value and a cumulative stop value from these data; Limiting the maximum value of the data in the histogram memory by the control data from the histogram arithmetic circuit,
A limiter / adder circuit for adding a constant value to each data and processing the data in the histogram memory; a histogram cumulative adder circuit for cumulatively adding the data in the histogram memory; a cumulative histogram memory for storing the operation result; An accumulative control register circuit for controlling start and stop values of the histogram accumulative addition processing in the histogram accumulative addition circuit based on the control data obtained by the arithmetic circuit, and a maximum value of the accumulative histogram memory obtained by the histogram arithmetic circuit A normalization control register circuit for controlling a normalization process of the data of the cumulative histogram memory; and a data corresponding to the data obtained after normalizing the data of the cumulative histogram memory under the control of the normalization control register circuit. A lookup table calculation circuit for calculating a subtraction gradation correction data in degrees level, and a look-up table which stores the result of the calculation, the first AD
A luminance correction operation circuit for performing gradation correction using a correction signal obtained from the look-up table using the output signal of the converter and the same signal as an address, and a first DA converter for converting the video signal after the calculation into an analog value And a second AD converter for converting an input color signal into a digital value, and dividing the output correction signal of the look-up table by a luminance level of a corresponding pixel to calculate an average value of two pixels of obtained data. Average value calculating circuit, and output data of the average value calculating circuit.
Multiplying the output color signal of the second A / D converter by
Gradation correcting apparatus calculates color correction data, then a color correction operation circuit for performing gradation correction, wherein the color signal after the operation to have a second DA converter for converting into an analog value by.