KR101257757B1 - Real time gamma correction - Google Patents

Abstract

The present invention relates to a real-time gamma correction method capable of processing gamma correction at zero cycle in an FPGA logic by performing gamma correction using only a subtractive operation. The present invention comprises the steps of: (a) calculating a first gamma correction output using a first gamma value that is a natural number; (b) calculating a second gamma correction output using a second gamma value that is a natural number higher than the first gamma value; (c) subtracting the second gamma correction output from the first gamma correction output to calculate a gamma correction output difference; calculating a third gamma correction output by multiplying and / or dividing a gamma correction output difference by a gamma factor corresponding to a value below a floating point of an actual gamma value; And (e) subtracting the third gamma correction output from the first gamma correction output, or adding the third gamma correction output to the second gamma correction output to calculate a final gamma correction output. Provide a calibration method.

Description

Real-time gamma correction method {REAL TIME GAMMA CORRECTION}

The present invention relates to a method for performing gamma correction in real time, and more particularly, to a real time gamma correction method for processing gamma correction in real time in a display device including an LED display.

In general, the human eye is more sensitive to brightness than color. This is because sensor cells in the human eye have an absolute number of cells that respond to brightness than cells that respond to color. However, the screen appears dark due to the distortion of the display device, and gamma correction is used to solve this problem.

Traditionally, gamma correction has been used to correct the nonlinearity of the CRT (Cathode Ray Tube). In the CRT, the luminance characteristic curve has a specific curve due to the use of fluorescent materials. In order to correct this, the broadcast station transmits the broadcast by inverse gamma using a nonlinear transfer function. The television receiver side gamma corrects the received broadcast signal to reproduce the image. Currently, display devices such as Plasma Display Panel (PDP), Liquid Crystal Display (LCD), Active Matrix Organic Light Emitting Diodes (AMOLED), and Light Emitting Diode (LED) display boards are being replaced by CRTs. It has a high market share. These new displays have high linearity unlike CRTs. However, broadcast equipment still transmits the image by inverse gamma, so gamma correction is required in new display devices.

Typically, the gamma value of CRT is 2.2, and gamma correction is performed using the formula "Y = X ^ 2.2". The gamma value may vary depending on the type of display device, and may also vary according to a product or a video mode selection in the same type of display device.

In the case of the previous analog broadcast reception, real-time gamma correction was relatively easy by forming differential circuits and integrating circuits using R, L, and C to pass video signals and adjusting gamma values using time constants. However, when receiving digital broadcasting, it is necessary to perform sub-floating square root operations in field programmable grid array (FPGA) logic, and it is impossible to process such complex operations in zero cycles even in a high-performance FPGA. When processing in multiple cycles using a CPU or a calculator, the operation can be simplified, but expensive components are required, and time delays due to multi-cycle processing are inevitably generated, and thus real-time gamma correction is not smooth.

1 illustrates gamma correction using a conventional gamma lookup table. Referring to FIG. 1, in order to gamma correct input image data, a plurality of gamma correction tables for storing different gamma values are required. Each gamma correction table is stored in storage devices 11, 13, and 15, for example, EEPROM (Electrically Erasable Programmable Read-Only Memory). When an 8-bit video input signal is input through the first mux 10, the storage devices 11, 13, and 15 are selected according to the gamma value required, and gamma correction is performed using the gamma correction table of the selected storage device. After the implementation, a 10-bit video output signal is output through the second mux 20.

However, in the case of operating a large number of gamma correction tables as shown in FIG. 1, "2 Byte * 3 Color (R, G, B) * 256 Byte" per one gamma table, that is, 1,536 Byte is inevitably considerably required. It will use a lot of memory. For example, when a plurality of local LED controllers are used, such as an LED display board, the number of required gamma correction tables is greatly increased, thereby increasing the storage capacity and causing a delay in the time required for the gamma correction operation.

Patent Application No. 10-2005-0123699 proposes a gamma correction method using two gamma correction tables as shown in FIG. In the related art, the gamma correction table is operated using only two storage devices 31 and 33 as in the example of FIG. 2, and the gamma correction value is calculated in real time and stored in the redundant table. However, even in such a method, the use of storage devices 31 and 33 such as RAM (Random Access Memory) is inevitable, and an operation device for square root calculation below the floating point is required, and it is still necessary to process gamma correction at zero cycle. There is a difficult problem.

On the other hand, in the case of the LED display board is required high definition (HD) or higher, the amount of real-time image data is gradually increasing. In general, an LED display board receives a video signal in real time, converts it in parallel, and transmits the same to a LLC (Local LED Controller) through a high-speed SDI (Serial Digital Interface). LED signboards have a large distance from the display surface to the DSP due to their characteristics, and so many LLCs are used in one screen. Therefore, when gamma correction is performed using a lookup table as in the related art, the cost of the video controller is greatly increased because the data transfer amount is greatly increased and the lookup table must be provided for each LLC. Furthermore, the delay of the gamma correction may cause malfunction of each LLC, leading to deterioration of display quality.

Patent Application No. 10-2005-0123699 Gamma correction method and apparatus of an electronic display device

The present invention does not require a calculation device for floating-point square root operation and a storage device for storing gamma values by performing a gamma correction using only an additive subtraction operation without using a complex operation such as floating-point square root operation for gamma correction. The purpose is to provide a new gamma correction method suitable for real-time gamma correction by performing gamma correction.

A real time gamma correction method according to an embodiment of the present invention includes: (a) calculating a first gamma correction output using a first gamma value that is a natural number; (b) calculating a second gamma correction output using a second gamma value that is a natural number higher than the first gamma value; (c) subtracting the second gamma correction output from the first gamma correction output to calculate a gamma correction output difference; calculating a third gamma correction output by multiplying and / or dividing a gamma correction output difference by a gamma factor corresponding to a value below a floating point of an actual gamma value; And (e) subtracting the third gamma correction output from the first gamma correction output, or adding the third gamma correction output to the second gamma correction output to calculate a final gamma correction output.

In the real-time gamma correction method according to another embodiment of the present invention, the first gamma value is "2", the second gamma value is "3", and the first gamma correction output of step (a), step (b) The second gamma correction output and the gamma correction output difference of step (c) are respectively calculated by the following equations (1), (2) and (3).

(Calculation 1)

(Calculation 2)

(Calculation 3)

는 제1 감마 보정 출력이고,

는 제2 감마 보정 출력이고,

는 감마 보정 출력 차분이고,

는 비디오 입력 신호이다.
here,

Is the first gamma correction output,

Is the second gamma correction output,

Is the gamma correction output difference,

Is the video input signal.

In the real-time gamma correction method according to another embodiment of the present invention, the third gamma correction output of step (d) is calculated by Equation 4 below.

(Calculation 4)

는 제3 감마 보정 출력이고,

는 감마 팩터이다.
here,

Is the third gamma correction output,

Is the gamma factor.

In the real-time gamma correction method according to another embodiment of the present invention, the final gamma correction output of step (e) is calculated by Equation 5 below.

(Calculation 5)

는 최종 감마 보정 출력에 의한 비디오 출력 신호이다.
here,

Is the video output signal by the final gamma correction output.

In the real-time gamma correction method according to another embodiment of the present invention, the final gamma correction output of step (e) is calculated by Equation 6 below.

(Calculation 6)

는 최종 감마 보정 출력에 의한 비디오 출력 신호이다.
here,

Is the video output signal by the final gamma correction output.

In the real-time gamma correction method according to another embodiment of the present invention, the gamma factor of step (d) is one of a natural number of 0 to 255 corresponding to a value below the floating point of the actual gamma value, table mapping, proportional operation, and Obtained by one of the offset operations.

According to the real-time gamma correction method of the present invention, gamma correction can be performed only by the addition / decrement operation, which can be sufficiently implemented in FPGA logic, and a separate operation device for performing a complex operation such as floating point or fractional square root is not required. Since no lookup table for calibration is used, a separate storage device for storing them is also unnecessary, and gamma correction can be performed in zero cycle, so that the display device can realize real-time gamma correction without delay, especially the local LED of the LED display board. When applied to a controller, it has the effect of reducing the cost and preventing malfunction due to the gamma correction delay.

1 is a block diagram illustrating a gamma correction using a conventional gamma lookup table.
2 is a block diagram illustrating gamma correction using two conventional gamma correction tables;
3 is a flowchart illustrating a real-time gamma correction method according to the present invention;
4 is a diagram illustrating a gamma correction program using VDHL in the present invention, and
5 illustrates a gamma graph according to an embodiment of the present invention.

Hereinafter, specific embodiments according to the present invention will be described with reference to the accompanying drawings. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Parts having similar configurations and operations throughout the specification are denoted by the same reference numerals. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

In describing the embodiments in detail, overlapping descriptions or descriptions of obvious technology in the art are omitted. Also, in the following description, when a section is referred to as "comprising " another element, it means that it may further include other elements in addition to the described element unless otherwise specifically stated.

 Also, the terms "to", "to", "to", and "modules" in the specification mean units for processing at least one function or operation, and may be implemented by hardware or software or a combination of hardware and software . In addition, when a part is electrically connected to another part, it includes not only a case directly connected but also a case where the other parts are connected to each other in the middle.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component.

3 is a flowchart illustrating a real-time gamma correction method according to the present invention. Referring to FIG. 3, the real-time gamma correction method of the present invention provides a method of performing gamma correction without performing a floating point square root (or fractional square root) operation. The "first gamma value" and "second gamma value" mentioned below are virtual gamma values, which are natural numbers, and have a larger value of "second gamma value" than "first gamma value". For example, if the actual gamma value is "2.2", the first gamma value may be "2" and the second gamma value may be "3". Thus, the first gamma value and the second gamma value are boundary values which are natural numbers before and after the actual gamma value.

Since the gamma value is generally located between 2 and 3, the following example illustrates a case where the first gamma value is "2" and the second gamma value is "3". However, it is a matter of course that the technical idea of the present invention may have a boundary value of a natural number different from that of the first gamma value and the second gamma value.

Referring to FIG. 3, first, a first gamma correction output is calculated using the first gamma value (ST110). In the present embodiment, the first gamma value is "2", and the first gamma correction output is calculated by Equation 1 below.

(Calculation 1)

는 제1 감마 보정 출력이고,

는 비디오 입력 신호이다.here,

Is the first gamma correction output,

Is the video input signal.

Next, a second gamma correction output is calculated using the second gamma value (ST120). In the present embodiment, the second gamma value is "3", and the second gamma correction output is calculated by the following equation (2).

(Calculation 2)

는 제2 감마 보정 출력이다.here,

Is the second gamma correction output.

Next, the gamma correction output difference is calculated by subtracting the second gamma correction output from the first gamma correction output (ST130). The gamma correction difference output is calculated by the following equation (3).

(Calculation 3)

는 감마 보정 출력 차분이다.here,

Is the gamma correction output difference.

The third gamma correction output is calculated by multiplying (by multiplying the gamma factor by 256) the gamma factor corresponding to the value below the floating point of the actual gamma value to the gamma correction output difference obtained by the equation (3) (ST140). The third gamma correction output is calculated by the following equation (4). On the other hand, the gamma factor is a factor for avoiding the complicated process of calculating the fractional square root of the floating point value of the actual gamma value, and may have a form different from Equation 4. The third gamma correction output may be calculated using the arithmetic.

(Calculation 4)

는 제3 감마 보정 출력이고,

는 감마 팩터이다.here,

Is the third gamma correction output,

Is the gamma factor.

)는 0 내지 255의 자연수 중 하나의 값을 가지며, 테이블 매핑, 비례 연산, 및 옵셋 연산 중 하나의 방법으로 구할 수 있다. 만약, 실제 감마값이 "2.2"라고 한다면, 부동 소수점 이하의 수인 "0.2"를 감마 팩터 테이블에 매핑한다. 도시하지 않았지만, 감마 팩터 테이블은 "0.00 ~ 0.99"의 숫자 테이블과 "0 ~ 255"의 자연수를 매핑하는 테이블이며, 예컨대 "0.2"에 대응하는 감마 팩터는 "51"이다.Gamma Factor

) Has one of natural numbers from 0 to 255, and can be obtained by one of table mapping, proportional operation, and offset operation. If the actual gamma value is " 2.2 " Although not shown, the gamma factor table is a table that maps a numeric table of "0.00-0.99" and a natural number of "0-255", for example, a gamma factor corresponding to "0.2" is "51".

According to the proportional calculation method, a gamma factor can be obtained by multiplying "0.2" by 256 and rounding off or rounding off the number after the decimal point. As another example, according to the offset operation method, a gamma factor can be obtained by assigning a designated gamma factor to the numbers "0.01 to 0.20" below the floating point and performing a table mapping or a proportional operation on "0.21 to 0.99". have. The section giving the offset may be changed in various ways.

Finally, the final gamma correction output is calculated using the first gamma correction output to the third gamma correction output (ST150). For example, the final gamma correction output may be calculated by subtracting the third gamma correction output from the first gamma correction output. In this case, Equation 5 below is used.

(Calculation 5)

는 최종 감마 보정 출력에 의한 비디오 출력 신호이다.here,

Is the video output signal by the final gamma correction output.

As another example, the final gamma correction output may be calculated by adding the third gamma correction output to the second gamma correction output. In this case, Equation 6 below is used.

(Calculation 6)

FIG. 4 is a diagram illustrating a gamma correction program using a VDHL (Very High Speed Integrated Circuit Hardware Description Language) according to the present invention, wherein a 10-bit video input signal is gamma-corrected to a 16-bit video output signal in an LED display. To illustrate.

Referring to FIG. 4, since the first gamma value and the second gamma value are natural numbers of "2" and "3", respectively, the first and second gamma correction outputs can be obtained by multiplying the video input signal only two and three times. have. The adjusted value of the gamma correction output is calculated by multiplying the gamma correction output difference by a value obtained by dividing the gamma factor of "0 to 255" by "256" (the value obtained by converting the floating point number of the actual gamma value into a digital expression).

Next, the final gamma correction output can be obtained by subtracting "gam0-9" from "gam20". In this case, as in the gamma graph shown in FIG. 5, the gamma curve of "Y = X ^ 2" is shifted to the gamma curve shown by the dotted line, so that a video output signal approximating the correction value using the actual gamma value can be obtained. .

Although not shown in FIG. 4, the final gamma correction output may be obtained by adding "gam0-9" to "gam30". In this case, a gamma curve of "Y = X ^ 3" is shown as a dotted line in the graph of FIG. 5. Shift to the gamma curve.

According to the real-time gamma correction method described above, the gamma correction can be completed only by the addition and subtraction operation as in the VDHL of FIG. 4, which means that the gamma correction can be processed with very little logic. Thus, gamma correction can be processed with zero cycles. In addition, since the square root operation below the floating point is not performed, no operation device or complicated logic is required, and the storage device is also unnecessary because the lookup table is not used.

The invention described above is susceptible to various modifications within the scope not impairing the basic idea. In other words, all of the above embodiments should be interpreted by way of example and not by way of limitation. Therefore, the scope of protection of the present invention should be determined in accordance with the appended claims rather than the above-described embodiments, and should be construed as falling within the scope of the present invention when the constituent elements defined in the appended claims are replaced by equivalents.

Claims (6)

(a) calculating a first gamma correction output using a first gamma value that is a natural number;
(b) calculating a second gamma correction output using a second gamma value that is a natural number higher than the first gamma value;
(c) subtracting the second gamma correction output from the first gamma correction output to calculate a gamma correction output difference;
calculating a third gamma correction output by multiplying and / or dividing a gamma correction output difference by a gamma factor corresponding to a value below a floating point of an actual gamma value; And
(e) subtracting the third gamma correction output from the first gamma correction output, or calculating the final gamma correction output by adding the third gamma correction output to the second gamma correction output.
Real time gamma correction method comprising a. The method of claim 1,
The first gamma value is "2", the second gamma value is "3", the first gamma correction output of step (a), the second gamma correction output of step (b), and the gamma of step (c) The correction output difference is calculated by the following equations 1, 2, and 3, respectively.
(Calculation 1)

(Calculation 2)

(Calculation 3)

here,

Is the first gamma correction output,

Is the second gamma correction output,

Is the gamma correction output difference,

Is the video input signal. The method of claim 2,
The third gamma correction output of the step (d) is calculated by the following equation (4).
(Calculation 4)

here,

Is the third gamma correction output,

Is the gamma factor. The method of claim 3,
The final gamma correction output of step (e) is calculated by the following equation (5).
(Calculation 5)

here,

Is the video output signal by the final gamma correction output. The method of claim 3,
The final gamma correction output of the step (e) is calculated by the following equation (6).
(Calculation 6)

here,

Is the video output signal by the final gamma correction output. The method of claim 3,
The gamma factor of step (d) is one of natural numbers from 0 to 255 corresponding to the floating point value of the actual gamma value, and is obtained by any one of table mapping, proportional operation, and offset operation. Gamma Correction Method.

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