JP3312509B2 - Gamma correction luminance level complementer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit,
The present invention relates to a device for compensating for a jump in luminance level caused by gamma correction.

[0002]

2. Description of the Related Art Since an NTSC signal has a characteristic (inverse gamma correction characteristic) corrected in advance so that it is displayed at an appropriate luminance level when displayed on a cathode ray tube, an input voltage-display output characteristic is obtained. Is displayed on a PDP (plasma display panel) or the like, which is different from a cathode ray tube, an appropriate luminance level cannot be obtained unless correction is performed. For this reason, a gamma correction circuit is provided to correct the luminance level characteristic. In this correction, for example, as shown in FIG. 3, correction is performed so that the luminance level in the middle region of the input signal becomes steep (→). When this correction is performed by digital processing, for example, a correction coefficient When the (gamma value) is 2, as shown in FIG.
Brightness level number = 8 output signal luminance level number 4 against, i.e. the number of luminance level is a half intensity level
Le jump occurs, there is a problem that image quality is significantly impaired.

[0003]

SUMMARY OF THE INVENTION In view of the above, the present invention considers pixels to be gamma-corrected on each pixel.
Find the average of the brightness levels of the bottom, left, and right pixels,
The purpose of this invention is to complement the luminance level of the gamma-corrected pixel with this average value and to moderate the luminance level difference from the surrounding pixels to prevent image quality deterioration.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention converts a video signal into a digital signal and performs gamma correction using a required gamma correction coefficient. Above the pixel to be processed,
Lower, an average value calculation means for calculating an average value of the brightness levels of the left and right of the pixel, the brightness level obtained by adding the required value on the luminance levels of the processed pixels and the upper limit of the threshold value, than the average value calculating means an upper limit threshold value comparing means for outputting a signal when the value exceeds the comparison upper threshold and upper threshold, bright obtained by subtracting the required value than the luminance level of the processed pixel
The degree levels and lower threshold, the lower threshold comparing means for outputting a signal if the does not reach a value of from the average value calculating means to the lower limit of the lower limit is compared with the threshold value threshold limit The luminance level of the pixel to be processed is
Bright summing the required value to the bell, or lower threshold comparison in signal from means formed by providing a brightness level complementary means for subtracting a predetermined value from the luminance level of the processed pixel gamma correction
A degree-level complement circuit is provided.

[0005]

With the above configuration, the gamma correction luminance level complementing circuit according to the present invention employs a
Calculate the average of the luminance levels of the lower, left and right pixels,
The luminance level of the pixel is complemented according to the calculated value. As a result, the jump of the luminance level caused by the gamma correction is reduced, and the deterioration of the image quality can be prevented.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a gamma correction luminance level complement circuit according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a main part of an embodiment of a gamma correction luminance level complementing circuit according to the present invention. In the figure, reference numeral 1 denotes an input terminal for inputting R (red), G (green) and B (blue) video signals. Reference numeral 2 denotes an A / D converter, which converts a video signal from the input terminal 1 into digital data. A gamma correction circuit 3 corrects the video signal of each color from the A / D conversion unit 2 using a required gamma correction coefficient. 4 is a delay circuit,
The data from the gamma correction circuit 3 is delayed by one clock (clock used in the signal processing system) and input to the adder 11. 5
Is a line memory, which stores data from the gamma correction circuit 3 as 1
After the line is recorded, it is read and input to the adder 11. A delay circuit 6 delays data from the line memory 5 by one clock. Reference numeral 7 denotes data to be processed which is extracted through the delay circuit 6. A delay circuit 8 delays the data from the delay circuit 6 by one clock and inputs the data to the adder 11. Reference numeral 9 denotes a line memory for recording one line of data read from the line memory 5. A delay circuit 10 delays the data read from the line memory 9 by one clock and inputs the data to the adder 11. A divider 12 divides the data from the adder 11 by the number of additions to calculate an average value.

Reference numeral 13 denotes a -n processing circuit which controls the brightness of the data 7 to be processed.
The n luminance level (n = 1 when the gamma correction value = 2) is subtracted from the degree level . Numeral 14 denotes a + n processing circuit which adds n luminance levels (n = 1 when the gamma correction value = 2) to the luminance level of the data 7 to be processed. A comparator 15 compares the data B from the divider 12 with the data A from the -n processing circuit 13, and outputs a signal a when B <A. 16 is a comparator,
The data B from the divider 12 is compared with the data A from the + n processing circuit 14, and if B> A, a signal b is output. Reference numeral 17 denotes a selector control gate which switches the selector 18 to the mn side by a signal a from the comparator 15 and switches the selector 18 to the m + n side by a signal b from the comparator 16;
When no signal is output, the selector 18 is switched to the m side.

Next, the operation of the luminance level complement circuit for gamma correction according to the present invention will be described. The video signals of each color of R, G, and B from the terminal 1 are converted into digital signals by the A / D converter 2 and input to the gamma correction circuit 3, and the image is displayed at an appropriate luminance level on a display used. Perform gamma correction to display. For example, when the display device is a PDP, the gamma correction is performed such that the luminance level in the middle range becomes steep as shown in the input data having the luminance level characteristic shown in FIG. The corrected data is input to the delay circuit 4 and the line memory 5, respectively. The delay circuit 4 delays the input data by one clock and inputs the data to the adder 11, and the line memory 5 records the input data for one line and reads it out. Enter 11 The data read from the line memory 5 is simultaneously input to the delay circuit 6 and the line memory 9, respectively. The data input to the delay circuit 6 is delayed by one clock, then further delayed by one clock in the delay circuit 8, input to the adder 11, and the data written in the line memory 9 is read out with one line delay. , 1 in delay circuit 10
The clock is delayed and input to the adder 11.

Thus, the processed data 7 output from the delay circuit 6 is added to the delay circuit 4 input to the adder 11.
Is the data of the pixel below the pixel to be processed,
The data from the line memory 5 is the data of the pixel to the right of the pixel to be processed, the data from the delay circuit 8 is the data of the pixel to the left of the pixel to be processed, and the data from the delay circuit 10 is the data of the pixel above the pixel to be processed. Data. On these in adder 11,
The four data of lower, left and right are added, and this is divided by a quarter by the divider 12 to calculate the average value B of the upper, lower, left and right pixels of the pixel to be processed.

The processed data 7 from the delay circuit 6 is
Input to the n processing circuit 13 and the + n processing circuit 14, for example,
When the gamma correction value is 2, the -n processing circuit 13 determines that the luminance level of the data 7 to be processed is one half of the gamma correction value from the luminance level.
The luminance level is subtracted to obtain a lower limit threshold value. This data is applied to the A terminal of the comparator 15 and the mn terminal of the selector 18, and the + n processing circuit 14 sets the luminance level of the data 7 to be processed.
The above-mentioned one luminance level is added to the threshold value to obtain an upper limit threshold value, which is applied to the A terminal of the comparator 16 and the m + n terminal of the selector 18. Then, the data B from the divider 12 is input to the comparator 15, and when data B <threshold A, a signal a is output to the selector control gate 17 as shown in FIG.
The data is switched to the n side, and the data obtained by subtracting one luminance level from the -n processing circuit 13 is output. Further, the data B from the divider 12 is input to the comparator 16, and when the data B> the threshold value A, the signal b is output to the selector control gate 17, and the selector b is output.
18 is switched to the m + n side, and one brightness from the + n processing circuit 14 is obtained.
The data with the level added is output. If the data from the divider 12 is greater than or equal to the lower threshold and less than or equal to the upper threshold, that is, if the signal a is not output from the comparator 15 and the signal b is not output from the comparator 16, the selector
18 is switched to the m side, and the data from the delay circuit 6 is output without complementation.

In the above description, the gamma correction value is 2, but when the gamma correction value is larger than 2, for example, 3, the upper and lower thresholds are set to ± 1/3 and ± 2. / 3 etc., and the data of the pixel to be processed is ± 1 /
If it is less than 3, output without complementing, + ／ to +2
If / 3 adds 1/3 of the gamma correction value to the luminance level of the processed pixel, + 2/3 or more bright of the processed pixel when
Adds 2/3 of the gamma correction value to the degree level , and subtracts 1/3 of the gamma correction value from the luminance level of the pixel to be processed when the data of the pixel to be processed is -1/3 to -2/3. Then-
For more than two-thirds may be to complement the jump luminance level by subtracting 2/3 of the gamma correction value from the brightness level of the processed pixel.

[0012]

As described above, according to the luminance level complementing circuit for gamma correction according to the present invention, the jump in luminance level caused by gamma correction is complemented according to the average luminance level of the pixels surrounding each pixel. And the brightness between adjacent pixels
Since the step of the degree level is made gentle, it is possible to prevent the image quality from deteriorating due to the gamma correction.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a luminance level complementing circuit for gamma correction according to the present invention.

FIG. 2 is a diagram for explaining outputs of comparators 15, 16 and a selector 18.

FIG. 3 is a diagram for explaining a luminance level jump.
(A) is an overall view, and (B) is a partially enlarged view.

[Explanation of symbols]

 3 Gamma correction circuit 4 1 clock delay circuit 5 Line memory 6 1 clock delay circuit 7 Data to be processed 8 1 clock delay circuit 9 Line memory 10 1 clock delay circuit 11 Adder 12 Divider 13 Δn processing circuit 14 + n processing circuit 15 Comparator 16 Comparator 17 Selector control gate 18 Selector

Claims (8)

(57) [Claims] A gamma correction circuit for converting a video signal into a digital signal and performing gamma correction with a required gamma correction coefficient;
Lower, an average value calculation means for calculating an average value of the brightness levels of the left and right of the pixel, the brightness level obtained by adding the required value on the luminance levels of the processed pixels and the upper limit of the threshold value, than the average value calculating means an upper limit threshold value comparing means for outputting a signal when the value exceeds the comparison upper threshold and upper threshold, bright obtained by subtracting the required value than the luminance level of the processed pixel
The degree levels and lower threshold, the lower threshold comparing means for outputting a signal if the does not reach a value of from the average value calculating means to the lower limit of the lower limit is compared with the threshold value threshold limit The luminance level of the pixel to be processed is
Bright summing the required value to the bell, or lower threshold comparison in signal from means formed by providing a brightness level complementary means for subtracting a predetermined value from the luminance level of the processed pixel gamma correction
Degree level completion circuit. 2. When the gamma correction value by the gamma correction circuit = 2, the upper limit threshold value is set to
Luminance les obtained by adding one-half of the gamma correction value to the luminance level
And Bell, the lower limit of the threshold, the luminance Le to be processed pixel
The luminance level complement circuit for gamma correction according to claim 1, wherein the luminance level is obtained by subtracting half of the gamma correction value from the bell . 3. The luminance level complementer adds one half of a gamma correction value to a luminance level of a pixel to be processed or a lower limit of a luminance when a signal from the comparator exceeds an upper threshold. If the threshold is not reached, the brightness of the pixel to be processed
Gamma corrected luminance level interpolation circuit of claim 2, wherein the the level to be subtracted one-half of the gamma correction value. 4. The means for calculating the average value of the pixels above and below the pixel to be processed, stores the data from the gamma correction circuit as 1
A first line memory for storing lines and a second line memory for storing data read from the first line memory for one line are provided, and data from the gamma correction circuit and data read from the second line memory are provided. 4. The gamma correction gradation complement circuit according to claim 1, wherein the circuit performs averaging. 5. An apparatus for calculating an average value of left and right pixels of a pixel to be processed, comprising:
A first delay circuit for delaying a clock, and a second delay circuit for delaying data from the first delay circuit by one clock, and averaging data from the gamma correction circuit and data from the second delay circuit. The gamma correction gradation complement circuit according to claim 1, 2 or 3. 6. An average value calculating means for upper, lower, left and right pixels of the pixel to be processed, comprising: a first line memory for storing one line of data from the gamma correction circuit; A second line memory that stores the read data for one line, a third delay circuit that delays the data from the gamma correction circuit by one clock, and a fourth delay that delays the data read from the first line memory by one clock A fifth delay circuit for delaying the data from the fourth delay circuit by one clock; and a sixth delay circuit for delaying the data read from the second line memory by one clock. 4. The method according to claim 1, wherein the data, the data from the first line memory, the data from the fifth delay circuit, and the data from the sixth delay circuit are added and averaged. The described gamma correction gradation complement circuit. 7. The averaging is performed by adding data from the third delay circuit, data from the first line memory, data from the fifth delay circuit, and data from the sixth delay circuit using an adder, and dividing the data. 7. The gamma correction gradation complement circuit according to claim 6, wherein the signal is divided by a factor of four. 8. The gamma correction gradation complement according to claim 7, wherein said divider uses two shift registers, shifts one bit at a time in each shift register, and calculates a quarter. circuit.