JP3685712B2 - Dynamic gamma correction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for dynamically optimizing a gamma correction table in order to improve the contrast of an image.
[0002]
[Prior art]
When displaying a moving image with a variable APL (average luminance level) such as a TV image on a display device such as an LCD or PDP that has a limited display gradation, the contrast of the display image is insufficient. No display image.
On the other hand, there is a method of increasing the gamma value near the APL, but there is a problem that the dynamic range is not sufficiently expanded.
A method for solving these problems is proposed in Japanese Patent Application Laid-Open No. 8-317250.
The method described in this publication will be briefly described according to the processing procedure.
First, the luminance level of the pixel of the video signal for each field or frame is detected, a histogram of the number of pixels for each luminance level is created, and based on the data obtained there, the minimum and maximum levels of the video signal are determined. calculate.
[0003]
FIG. 2 is a diagram showing an example of a histogram created by this conventional method.
The horizontal axis represents the luminance level, and the vertical axis represents the number of pixels (appearance frequency, hereinafter referred to as “frequency”).
On the histogram created in this way, the minimum level is determined as the minimum luminance level whose frequency exceeds a certain value (TH), and the maximum level is determined as the maximum luminance level whose frequency exceeds a certain value (TH). To do.
As this TH value, for example, a value of 1% of the total number of pixels in one field or one frame is set.
The reason for determining the minimum and maximum levels in this way is simply to determine the minimum and maximum brightness levels of all pixels. This is because it cannot be determined.
Next, a gamma correction lookup table having an input / output characteristic in which the minimum level and the maximum level obtained by expanding the range of the calculated minimum level to the maximum level to the full gradation width of the output video signal level is connected by a straight line is created.
[0004]
FIG. 3 is a diagram showing an example of input / output characteristics of the gamma correction lookup table created in this way.
In the figure, c2 is the original linear input / output characteristic, and cl represents the input / output characteristic created by this method.
Finally, the input / output characteristics optimized for each field or frame are applied to the input video signal as a gamma correction lookup table, so that an image with improved contrast can be obtained.
[0005]
[Problems to be solved by the invention]
However, in the above conventional apparatus, the frequency of appearance is counted by a frequency counter for every gradation, a histogram is created, and the minimum level and the maximum level of the luminance of the input video signal are determined. Therefore, the circuit configuration is complicated. There was a problem in terms of cost.
The present invention has been made to solve these problems, and an object of the present invention is to provide a dynamic gamma correction apparatus capable of obtaining the same effects as those of the prior art with a simple circuit configuration.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned purpose, a luminance distribution counter capable of setting the range is introduced, the minimum level and maximum level of the luminance of the input signal are derived, and based on this, the gamma look-up table data is optimized, The contrast is increased.
[0007]
The present invention, in the dynamic gamma correction apparatus of a display device displaying a television image or the like, among all the pixels of the video signal, the minimum pixel brightness level range power and the pixel having the maximum luminance level within the limits set in advance a power, and a counting means for counting for each field or each frame, said from the obtained frequency count means, the next field or the minimum brightness level range to be counted the frequency of pixels in the frame and the maximum luminance level calculation means for calculating the boundary value between the range, the feedback control means and a minimum luminance level range and maximum brightness level range obtained by the calculated detection means, resetting during the blanking period of the video signal , and a minimum boundary value of the maximum boundary value and maximum brightness level range of the minimum brightness level range obtained by the calculation means, profit as the luminance distribution data of the video signal And, for each field or frame, in which so as to optimize the gamma correction table of the input and output characteristics.
[0008]
The present invention further in the dynamic gamma correction apparatus, the count hand stage, the minimum boundary value of the minimum brightness level range is fixed to "0" in the minimum gradation level, change calculated by the calculating means the maximum boundary value of said minimum brightness level range that is as a variable, and the black level power counter for counting the frequency of pixels in said minimum brightness level range of the maximum luminance level range to be changed is calculated by the calculating means Using the minimum boundary value as a variable , the maximum boundary value of the maximum luminance level range is fixed to “maximum gradation level” , and the white level frequency counter is used to count the frequency of pixels in the maximum luminance level range . Is.
[0009]
The present invention further in the dynamic gamma correction apparatus, the calculating means for calculating the minimum luminance level range and the maximum luminance level range, and the frequency of the pixels in the minimum luminance level range obtained from each of said counter means a frequency of the pixels in the maximum luminance level range, as set by changing the minimum boundary value of the maximum boundary value and a maximum brightness level range of the minimum brightness level range so as to approach a predetermined frequency a predetermined It is a thing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a dynamic gamma correction apparatus according to the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a configuration of a dynamic gamma correction apparatus according to the present invention.
The dynamic gamma correction apparatus of the present invention counts the total number of pixels within a specified range of the luminance level for each field or frame, and an A / D converter 1 that converts an input video signal into digital data. A luminance count unit 2, a range generating unit 3 for resetting the range from the frequency obtained by the luminance counter unit 2, a gamma generating unit 4 for generating an optimized gamma correction lookup table, and a gamma correction lookup The gamma correction unit 5 performs gamma correction according to the table, and the D / A conversion unit 6 converts the analog data.
[0011]
The input video signal is a Y (luminance) signal or an RGB signal.
In the case of an RGB signal, three systems are required for the A / D conversion unit 1, the gamma correction unit 5, and the D / A conversion unit 6, and the RGB signal is converted into a luminance signal through a matrix circuit (not shown). In addition, the luminance count is sent to the evening part 2.
Further, the luminance signal has an 8-bit gradation.
In the A / D conversion unit 1, the video signal converted into digital data is sent to the luminance count unit 2, and the frequency of the luminance distribution is counted.
[0012]
In the conventional method, the minimum level of the input video signal, in order to calculate the maximum level, and the count for each all gradation, had a histogram, luminance counter unit 2 in the present invention, all gradation A black level counter that counts the frequency of pixels in the range from the fixed value 0 of the minimum boundary value to the variable X of the maximum boundary value as the minimum luminance level range , instead of counting the frequency of each pixel ; The brightness level is composed of only two counters, a white level counter that counts the frequency of pixels in the range from the minimum boundary value variable Y to the maximum boundary value fixed value 255 (maximum gradation value) as the maximum brightness level range. ing.
These two counters are reset for each field or frame by synchronizing the video signal.
Here, the count values counted by the black level counter and the white level counter are referred to as a black level frequency and a white level frequency, respectively.
These are sent to the range generator 3 via the path 2a for each field or frame.
[0013]
In the range generation unit 3, if a value of 1% of the total number of pixels in one field or one frame (similar to the conventional example) is set to a predetermined predetermined frequency TH from the received black level frequency and white level frequency, Variables X and Y are changed as follows.
When black level frequency> TH, X → X-1
When black level frequency ≤ TH, X → X + 1
When white level frequency ≧ TH, Y → Y + 1
When white level frequency <TH, Y → Y-1
[0014]
The X and Y values changed in the range generating unit 3 in this way are returned to the luminance count unit 2 during the blanking period of the video signal through the path 3a, and the black level counter and the white level counter are respectively set. It is reset as a new boundary value indicating the minimum luminance level range and the maximum luminance level range to be counted , and the next field or frame is counted in this reset range.
The luminance count unit 2 and the range generation unit 3 constitute a feedback loop.
By forming such a feedback loop, when the video signal is a still image, the black level frequency and the white level frequency converge to the TH value.
Therefore, the variable X at that time is a luminance level at which the luminance level corresponds to a position having a frequency of 1% from the smallest. That is, the value of the minimum level calculated from the conventional histogram is almost equal to the value of X.
Similarly, the maximum level value calculated from the conventional histogram and the Y value are substantially equal.
[0015]
Therefore, in the present invention, the variable X indicating the maximum boundary value of the minimum luminance level range is set as the minimum level of the luminance level, and the variable Y indicating the minimum boundary value of the maximum luminance level range is set as the maximum level of the luminance level. Similarly, a gamma correction lookup table having input / output characteristics in which the range from the minimum level X to the maximum level Y is expanded to the full gradation width of the output video signal level is created.
On the other hand, when the video signal is a moving image, the values of the minimum level and the maximum level determined by the method of the present invention are not accurate as the video information at that moment because the feedback cannot follow. Become.
On the other hand, in the case of actually performing dynamic gamma correction, the gamma correction table is not optimized according to the information at that moment, and the LPF is applied in the time axis direction to change the table in the time axis direction. It is slowing down. This is because if the gamma correction table is changed greatly for each moment, problems such as flashing of background brightness occur.
However, the determination result of the minimum level and the maximum level according to the present invention is not much different from that obtained by multiplying the LPF in the time axis direction, and functions sufficiently as a parameter for dynamic gamma correction. Therefore, the LPF circuit in the time axis direction can be omitted.
[0016]
The minimum level and maximum level determined by the method of the present invention are sent to the gamma generation unit 4 and, as in the conventional method, from the obtained minimum level and maximum level, as shown in FIG. Generate a gamma correction look-up table connecting the lines with straight lines.
Then, the gamma correction unit 5 performs gamma correction on the video signal supplied from the A / D conversion unit 1 according to the gamma correction lookup table generated by the gamma generation unit 4.
Finally, the D / A converter 6 converts the dynamic gamma-corrected digital data into an analog signal to be supplied to a display unit (not shown) composed of an LCD or PDP, and the final output video Complete the signal.
With this output video signal, as described in the conventional method, a video with good contrast utilizing the maximum output dynamic range can be obtained.
[0017]
The method for changing the variables X and Y described above is the simplest method.
Actually, in order to stabilize the values of X and Y, when the frequency approaches the TH value, a dead zone for maintaining the values of X and Y as they are is provided, or a hysteresis characteristic is provided so as not to vibrate, When the frequency is significantly different from the TH value, the value of X or Y may be increased or decreased at once.
Further, in addition to the gamma correction characteristic in which the minimum level and the maximum level shown in FIG. 3 are connected by a straight line, the number of counters can be increased, and intermediate luminance distribution information can be introduced for use in optimizing the gamma table. Is possible.
It is also possible to use elements other than the minimum level and the maximum level, such as APL, for optimizing the gamma table.
[0018]
【The invention's effect】
As described above, according to the dynamic gamma correction apparatus according to the present invention, the histogram is created from the frequency counters for all the gradations of the video signal as in the prior art, and the minimum level and the maximum level are calculated. Thus, the number of frequency counters can be significantly reduced.
In addition, since there is an LPF effect on the time axis, a smooth change on the time axis of the gamma table is facilitated.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a configuration of a dynamic gamma correction apparatus according to the present invention.
FIG. 2 is a diagram showing an example of a histogram created by a conventional method.
FIG. 3 is a diagram illustrating an example of input / output characteristics of a gamma correction lookup table.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... A / D conversion part, 2 ... Luminance counter part, 3 ... Range generation part, 4 ... Gamma generation part, 5 ... Gamma correction part, 6 ... D / A conversion part

Claims (3)

In dynamic gamma correction apparatus of a display device displaying a television image or the like, among all the pixels of the video signal, the pixels of the frequency and maximum brightness levels within range of the pixels in the minimum luminance level range set in advance and the frequency, boundary counting means for counting each or every frame field, from the obtained frequency by said counting means, a minimum luminance level range and maximum brightness level range to be counted the frequency of pixels in the next field or frame calculation means for calculating a value, and feedback control means for the minimum luminance level range and maximum brightness level range obtained by the calculated detection means, resetting during the blanking period of the video signal, the calculating means a minimum boundary value of the maximum boundary value and maximum brightness level range of the minimum brightness level range obtained by, using the luminance distribution data of the video signal, 1 off Rudo or every frame, dynamic gamma correction apparatus characterized by optimizing the gamma correction table of the input and output characteristics. The count hand stage, the minimum minimum boundary value of the luminance level range is fixed to "0" of the minimum gradation level, the maximum boundary value variables said minimum brightness level range is changed calculated by said calculation means and a, outermost and the black level power counter for counting the frequency of pixels in a small luminance level range, the minimum boundary value of the maximum luminance level range to be changed is calculated as a variable by the calculation means, the said maximum luminance level range 2. The dynamic gamma correction according to claim 1, comprising a white level frequency counter for fixing the maximum boundary value to “maximum gradation level” and counting the frequency of pixels in the maximum luminance level range. apparatus. Minimum luminance level range and said calculating means for calculating the maximum luminance level range, a frequency of the pixels in the frequency and the maximum brightness level range of the pixels in the minimum luminance level range obtained from each of said counter means and said, 3. The dynamic gamma correction according to claim 1, wherein the maximum boundary value of the minimum luminance level range and the minimum boundary value of the maximum luminance level range are changed and set so as to approach a predetermined frequency. apparatus.

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