JPH05211659A - Gamma correcting circuit and method - Google Patents

Abstract

PURPOSE: To shorten the time required for gamma correction by simplifying the process of gamma correction by performing gamma correction with software so that the hardware constitution can be made simpler. CONSTITUTION: Gamma correction is performed by using operational expressions for gamma correction for each state of a gamma correcting circuit 300 by comparing the magnitude of inputted R, G, or B signals with the magnitudes of relative values A and B corresponding to the R, G, or B signals by means of a comparing section 100 when the values of the R, G, or B signals are assumed to be 100% and the final video signal is 100 IRE and switching the switch SW4 of a switching section 200 based on the compared results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing system such as a color television or a video camera, and more particularly to a real-time digital image processor capable of high-speed operation without the need for a separate external hardware configuration. The present invention relates to a gamma correction circuit and method in which an input is classified into a plurality of types and a subroutine is created for each of the inputs to enable gamma correction in real time.

[0002]

2. Description of the Related Art Generally, a gamma correction circuit is a correction circuit which is inserted on the image sending side in order to reproduce a sufficient color when a video signal is processed by a color television or a video camera. That is, since the luminance signal has a non-linearity such as a log waveform that is not directly proportional to the input signal on the image receiving side, this is a circuit to be inserted on the image transmitting side to compensate for the linearity.

FIG. 1 shows a conventional gamma correction circuit diagram.
R (Red), which is analog / digital converted by bits,
Each signal such as G (Green) and B (Blue) is accepted via the switches SW1 to SW3. Meanwhile, 256
The gamma-corrected data is stored and stored in a ram array having a capacity of × 8 bits. The above-mentioned lam array is called a lookup table, and its concept is schematically shown in FIG.
As shown in FIG. 2, it has 256 addresses. Since each of R, G, and B is composed of 8-bit data, it represents 256 kinds of states of the input signal, and thus has such a memory structure. At this time, the 8-bit R, G, B signals are not yet gamma-corrected, so this data is considered as an address and the data at the specific address of the lamb array is designated and called, and this signal is gamma-corrected. Output as. For this reason, gamma-corrected signals are closely packed in the RAM array, and no matter what data is input as an input signal, the central processing unit (CPU) controls the address to output the corresponding data,
The control generates a control signal to perform the gamma correction as described above during the blanking period.

Therefore, in a conventional gamma correction circuit, a digital image processing ASIC (Applicati
On Specific IC) is required, and at the same time, a microcomputer (central processing unit) and a central processing unit that control it must be used. At this time, since the central processing unit and the digital image processing chip have to be separated from each other, there is a drawback that the hardware for the interface of the two ICs becomes complicated. In addition, since it is difficult to know the exact change relation for gamma-correcting the input of the ram array, when the ASIC chip is developed, the cut-and-try method is used to repeatedly store the data in the memory, so that the gam array can be accurately corrected. There is a problem in that much time is consumed to store the corrected data.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve such a problem, and an object of the present invention is to utilize a real-time digital image processing processor capable of high-speed operation and to implement the same in the processor. It is an object of the present invention to provide a gamma correction circuit and method capable of performing gamma correction with a simple hardware configuration by performing gamma correction by software.

[0006]

The features of the present invention for attaining the above object are that R, G, or R which is connected to an input terminal IN of an R, G, or B signal and is input from the input terminal IN. A comparison unit 100 that compares the magnitude of the B signal with the magnitudes of relative values A and B when the R, G, or B signal value when the final video signal is 100 IRE is assumed to be 100%; A switching unit 200 connected to the input terminal IN and switched to perform gamma correction corresponding to the output of the comparison unit 100;
Gamma correction circuit 30 connected to 00 to perform gamma correction corresponding to the switching result of the switching unit 200.
0 in the gamma correction circuit.

A different feature of the present invention is a gamma correction method using a real-time digital image processor,
Comparing the magnitude of the input R, G, or B signal with the magnitude of the relative value A, B relative to that when the R, G, or B signal value when the final video signal is 100 IRE is assumed to be 100%. The first process to do,
And a second step L2 for performing gamma correction based on the comparison result of the first step.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 3A and 3B are a block diagram and a detailed circuit diagram of a gamma correction circuit using the real-time digital image processor of this embodiment. The comparison unit 100 and the switching unit 200 are connected to an input terminal IN of an R, G, or B signal (hereinafter described as “X”). The comparison unit 100 determines that the size of X input from the input terminal IN and the final video signal are 100IR.
The magnitudes of relative values A and B based on the X value when E is 100% are compared. The switching unit 200 uses a switch SW to perform gamma correction corresponding to the output of the comparison unit 100.
4 is switched. In the above, for example, 5 ≦ A ≦ 7,28
≦ B ≦ 32.

The switching unit 200 includes:
According to the switching result of the switching unit 200,
The gamma correction circuit 300 that performs the corresponding gamma correction is connected. When the input X value is smaller than the relative value A defined above, the gamma correction circuit 300 calculates the arithmetic expression Y.
= First gamma correction unit 310 that performs gamma correction with aX
When the input X value is an intermediate value between the relative values A and B defined above, the second gamma correction unit 320 that performs gamma correction by the arithmetic expression Y = bX + c, and the input X value is When it is larger than the relative value B to be defined, the arithmetic expression Y = dX
And a third gamma correction unit 330 that performs gamma correction with + e.

FIG. 5 is a flow chart for carrying out the gamma correction method using the real-time digital image processor of this embodiment. Compare the magnitude of the input R, G, or B signal with the magnitude of the relative value A, B relative to it, assuming that the R, G, or B signal value when the various video signals are 100 IRE is 100%. The first process L1 and the second process L2 that performs gamma correction based on the comparison result of the first process L1.

As described above, in this embodiment, the comparison unit 100
When assuming that the X value when the final video signal is 100 IRE is 100%, the X value input from is compared with the relative value (A, B) to the X value, and the switch of the switching unit 200 is switched according to this comparison result. SW4 is switched. That is, when the comparison result X value of the signal is smaller than A, the switch SW4 is switched to the terminal P1 to perform the gamma correction with the arithmetic expression "Y = aX", and when X is between A and B, The switch SW4 is switched to the terminal P2 so that the arithmetic expression “Y = bX
The gamma correction is performed by + c ", and when X is larger than B, the switch SW4 is switched to the terminal P3 so that the gamma correction is performed by the arithmetic expression" Y = dX + e ". ≦ 6,1 ≦ b ≦ 1.5, 20 ≦ c
≤25, 0.5 ≤ d ≤ 0.59, 41 ≤ e ≤ 45 are values selected from the experimental values so that the gamma correction is preferably performed.

The process L2 of performing the gamma correction will be described in more detail with reference to the flowchart of FIG. First, the subroutine created by the corresponding equations is executed according to the X value. That is, the X value is compared with the A and B values (S1),
When X <A, the gamma correction is performed by executing the subroutine of the arithmetic expression Y = aX (S2), and when A ≦ X ≦ B, Y
= BX + c subroutine to perform gamma correction (S3). When B <X, Y = dX +
Subroutine e is performed to perform gamma correction (S
4). That is, when the gamma correction is performed as described above, the gamma correction has a waveform diagram having an input / output transfer characteristic as shown in FIG. 4A.

A specific example of performing the gamma correction by the above arithmetic expression is as follows. For example, A =
6, B = 30, a = 5, b = 5/4, c = 22.5, d
= 4/7 and e = 300/7, the input / output transfer characteristic waveform diagram is as shown in FIG. 4B, where (1) section is Y = 5X and (2) section is Y = 5. / 4X
The +22.5 and (3) sections are gamma-corrected by Y = 4 / 7X + 300/7. In the drawing, E is a case where the input X value when the final video signal is 100 IRE is assumed to be 100% as in the case of A and B, and the value is a relative value to "100".

As described above, the present embodiment assumes that the magnitude of the input R, G or B signal and the R or G or B signal value when the final video signal is 100 IRE is 100%. In this case, the switch SW4 of the switching unit 200 is switched according to the comparison result of the comparison unit 100 that compares the relative values A and B with the relative values A and B, and the gamma correction is performed according to each state of the gamma correction circuit 300. The gamma correction is performed by the arithmetic expression of.

In this embodiment, three gamma correction units are provided to perform the approximation, but it is naturally possible to correct more accurately by providing a large number of gamma correction units. Further, depending on the type of image to be processed and the characteristics of the processing elements, it is possible to provide a rough correction part performed by one gamma correction part and an accurate correction part by a large number of gamma correction parts. Further, the number of gamma correction units is also determined from the image quality requirement and cost.

[0016]

As described above, the present invention is based on TI (Texas Ins
By using a real-time digital image processor capable of high-speed computation such as SVP (Senal Video Precessor) of Trument), the input is classified into a plurality of types, and a subroutine is created for each to perform gamma correction. , The circuit is simpler because no separate hardware configuration is required, and the gamma correction is processed by software, so that the processing is simpler and the time consumption is smaller than when using a conventional lamb array. is there.

[Brief description of drawings]

FIG. 1 is a conventional gamma correction circuit diagram.

FIG. 2 is a schematic representation of a look-up table used in a conventional gamma correction circuit.

FIG. 3A is a block diagram of a gamma correction circuit using the real-time digital image processor of the present embodiment.

FIG. 3B is a detailed circuit diagram of a gamma correction circuit using the real-time digital image processor of the present embodiment.

FIG. 4A is a waveform diagram of input / output transfer characteristics of the present embodiment.

FIG. 4B is a diagram showing a specific example of a waveform diagram of the input / output transfer characteristic of the present embodiment.

FIG. 5 is a flow chart for performing a gamma correction method using the real-time digital image processor of the present embodiment.

Claims (12)

[Claims] 1. An input terminal I for R, G or B signals.
The size of the R, G, or B signal that is connected to N and is input from the input terminal IN and the final video signal is 10
Relative values A and B when the R, G, or B signal value when 0IRE is assumed to be 100%
And a switching unit 200 connected to the input terminal IN and switched to perform gamma correction corresponding to the output of the comparison unit 100, and a switching unit 200 connected to the switching unit 200. And a gamma correction circuit 300 that performs gamma correction corresponding to the switching result of the switching unit 200. 2. The gamma correction circuit 300, when the input R, G, or B signal value is smaller than the relative value A, performs gamma correction by an arithmetic expression Y = aX (R, G, or B signal value). When the input R, G, or B signal value is an intermediate value between the relative values A, B, the first gamma correction unit 310 and the gamma correction by the arithmetic expression Y = bX (R, G, or B signal value) + C And a second gamma correction section 320 for performing the gamma correction with the arithmetic expression Y = dX (R or G or B signal value) + e when the input R, G or B signal value is larger than the relative value B. The gamma correction circuit according to claim 1, further comprising a third gamma correction unit 330. 3. The gamma correction circuit according to claim 1, wherein the magnitudes of the relative values A and B are 5 ≦ A ≦ 728 ≦ B ≦ 32. 4. The gamma correction circuit according to claim 2, wherein the magnitude of the a value is 4 ≦ a ≦ b. 5. The gamma correction circuit according to claim 2, wherein the magnitudes of the b and c values are 1 ≦ b ≦ 1.5 20 ≦ c ≦ 25. 6. The gamma correction circuit according to claim 2, wherein the magnitudes of the d and e values are 0.55 ≦ d ≦ 0.594 1 ≦ e ≦ 45. 7. A gamma correction method using a real-time digital image processor, wherein the R or G or B signal input and the R, G or B signal when the final video signal is 100 IRE. It is characterized by comprising a first step of comparing relative values A and B with respect to the value assuming that the value is 100%, and a second step L2 of performing gamma correction according to the comparison result of the first step. Gamma correction method. 8. In the second step, when the value of the R, G, or B signal input as a result of the comparison in the first step L1 is smaller than the relative value A, the arithmetic expression Y = aX (R, G, or B If the value of the R, G, or B signal input as a result of the comparison in the first process L1 is an intermediate value of the relative values A and B, a calculation formula Y = bX (R or G or B signal value) + c, and a step of performing gamma correction, and if the value of the R, G or B signal input as the comparison result of the first process L1 is larger than the relative value, an arithmetic expression 8. The gamma correction method according to claim 7, further comprising the step of performing gamma correction according to Y = dX (R or G or B signal value) + e. 9. The gamma correction method according to claim 8, wherein the magnitudes of the relative values A and B are 5 ≦ A ≦ 728 ≦ B ≦ 32. 10. The gamma correction method according to claim 8, wherein the range of the a value is 4 ≦ a ≦ b. 11. The gamma correction method according to claim 8, wherein the magnitudes of the b and c values are 1 ≦ b ≦ 1.5 20 ≦ c ≦ 25. 12. The gamma correction method according to claim 8, wherein the magnitudes of the d and e values are 0.55 ≦ d ≦ 0.594 1 ≦ e ≦ 45.