KR20000008780A - Gamma correction device of digital video data and gamma correction method - Google Patents

Abstract

PURPOSE: A gamma correction device of a digital video data improves a round-off error in a multiplier by using a floating multiplier having a simple structure, makes the offset data being input to an adder always have a positive value, and enhances a signal processing accuracy when correcting a gamma and de-gamma of LCD. CONSTITUTION: A gamma correction device of a digital video signal data includes a coder(130) for receiving a digital video signal data, and generating a predetermined code signal corresponding to a period involving a level of the digital video signal data. A memory(140) stores each period amplification coefficient N, each period coefficient data amplified as N times of a slope of approximate straight line of each period, and offset data of the approximate straight line of each period into a predetermined position. According to the code signal generated from the coder, the memory(140) generates an amplification coefficient N of the period involving a level of the digital video signal data, a coefficient data and offset data. A multiplier(150) multiplies the digital video signal data by the coefficient data from the memory, and generates the result. A divider(180) divides the output result of the multiplier by the amplification coefficient N from the memory, and generates the result. Adder(160) adds the output result of the divider to the offset data from the memory, and generates a gamma-corrected digital video signal data. Thereby, a round-off error is reduced in the multiplier, thereby increasing the accuracy of the gamma correction signal processing.

Description

Gamma Correction Device and Gamma Correction Method of Digital Image Signal Data

The present invention relates to a gamma correction apparatus and a gamma correction method of digital image signal data, and more particularly, by using a floating multiplier having a simple structure, the rounding error in the multiplier is improved and offset data input to the adder is added. The present invention relates to a gamma correction device for digital image signal data for improving the accuracy of signal processing during gamma correction of a camcorder and de-gamma correction of an LCD.

In general, the output characteristics of the electron beam emitted to the shadow mask in the CRT (Cathode Ray Tube) are not given linearly in response to the image signal applied to the electron gun, and are generally 2.2 power (Y = X) for the magnitude of the input signal. ^2.2 , where Y = Output Level, X = Input Level) increases exponentially. As a result, the brightness and the color of the image displayed on the screen are suddenly changed.

Therefore, there is that to compensate for the response characteristic of the CRT prevent image abrupt change in brightness and color of the displayed on the screen, an inverse function of the above exponential function as shown in Fig. 2 on the same transmitter and wherein the camcorder (Y = X ^{1 /2.2} = X ^0.45 , gamma coefficient gamma correction device having a response characteristic of?

Recently, as the technology of processing video signals digitally is widely used, a gamma correction device composed of digital circuits is used. Typically, gamma correction characteristics of input to output are converted into memory by corresponding input video signals to specific addresses of the memory. A mapping system that obtains a gamma characteristic of a video signal by storing the data in advance in a memory and outputting a gamma-corrected output signal stored at a corresponding address in the memory according to the level of the input video signal is well known. The gamma characteristic of the mapping system is divided into a plurality of sections according to the level of the input signal, and a gamma characteristic approximated by a polygonal line formed by connecting a series of approximated straight lines approximated to the gamma characteristic curve for each section. A gamma correction device for performing gamma correction using a curve is known.

However, in the above-described mapping system, since all points of the response characteristic curve for gamma correction must be stored in the memory, the memory capacity becomes large. In particular, when the gamma correction device is to be implemented as an integrated circuit, the increased memory capacity becomes a big obstacle.

On the other hand, gamma signal processing has been performed using a look-up table for the nonlinear signal processing as described above. However, when the input video signal is 10 bits and the output signal is 8 bits, 1024 × Not only does it require large amounts of 8-bit memory, it's also not easy to download this data from a microcomputer.

Accordingly, in order to reduce the capacity of the memory, a gamma correction device has been invented which can easily implement gamma correction signal processing using a multiplier and an adder, as disclosed in US Patent No. 5,243,426, which is a basic configuration of the device. As shown in 1.

In FIG. 1, reference numeral 10 denotes a CCD (Charge Coupled Device) image sensor 10 (hereinafter referred to as an image sensor) that converts an optical signal introduced into a camcorder through a lens into an electrical signal, that is, an image signal.

The analog-to-digital (A / D) converter 20 converts an image signal received through the image sensor 10 into digital image signal data X and applies it to the encoder 30 and the multiplier 50, respectively. .

The encoder 30 converts the digital video signal data X applied from the A / D converter 20 into a specific address of the memory 40 and applies it to the memory 40.

The memory 40 is composed of, for example, random access memory (RAM), and coefficient data A _n and Y intercepts, which are slopes of approximated straight lines in each section, to define a polygonal line approximating a gamma characteristic curve. In offset data B _n is stored. The coefficient data An and the offset data B _n stored in the memory 40 are stored and read in accordance with the address of the memory output from the encoder 30. That is, according to the level of the digital image signal data X applied to the encoder 30, the encoder 30 outputs a predetermined address of the memory 40 and accordingly the coefficient data A _n and the offset stored at the corresponding address of the memory 40. Data B _n is applied to multiplier 50 and adder 60, respectively.

The multiplier 50 multiplies the digital image signal data X input from the A / D converter 20 by the coefficient data A _n input from the memory 40 and outputs the result (A _n × X) to the adder 60. .

The adder 60 adds the offset data B _n output from the memory 40 to the result output from the multiplier 50 and outputs the result (A _n × X + B _n ) as gamma-corrected digital image signal data Y. .

FIG. 2 is a diagram schematically illustrating a method of approximating a gamma characteristic curve by using the gamma correction apparatus of the digital image signal data of FIG. 1. FIG. 2 illustrates an approximation method of the gamma characteristic curve in the gamma correction apparatus of FIG. If described with reference to:

In order to obtain the approximated gamma characteristic curve, that is, the polygonal line approximating the original gamma characteristic curve, the input signal level is divided into the appropriate number of sections, and the approximate straight lines corresponding to the original gamma characteristic curve are defined for each section, Connect with approximation straight line of adjacent section.

Each address of the memory 40 stores coefficient data A _n and offset data B _n as shown in FIG. 2 to define an approximate straight line in a corresponding section.

In FIG. 2, X _n-1 and X _n represent both boundary points of the _nth section {X _n-1 , X _n }, that is, the section start point and the section end point, and Y _n-1 and Y _n respectively represent the input image signal. Indicates the level of the output signal when the levels are X _n-1 and X _n . In addition, the coefficient data A _n applied to the multiplier 50 is an inclination of the approximate straight line in the _nth interval (X _n-1 , X _n } where n is an integer of 1 or more, which is expressed by Equation 1 below. The offset data B _n applied to the adder 60 means the Y-intercept of the approximate straight line in the _n- th section {X _n-1 , X _n }.

Therefore, the gamma-corrected digital image signal data Y finally output from the adder 60 can be represented by Equation 2 below.

Y = A _n × X + B _n

The gamma correction apparatus of FIG. 1 does not need to store output values for all points on the approximated gamma characteristic curve, but only the coefficient data A _n and offset data B _n in each section can be stored, thereby reducing the memory capacity. The size of the circuit constituting the compensator is also reduced.

However, the gamma curve of the camcorder is not fixed, but the slope may change from time to time depending on the user's operation mode selection such as low light mode and back light mode or the histogram equalizer. In particular, when the energy of the image signal is concentrated at a low level, such as in the low light mode, the slope of the gamma characteristic curve, that is, the approximate straight line, has a very small value in a portion over 100% white.

When gamma correction is performed using the gamma correction device of FIG. 1, when the slope of the approximate straight line approaches zero, the round-off error generated by the multiplier 50 increases, resulting in an output from the multiplier 50. You will get an error.

For example, to perform the gamma correction function with a digital floating multiplier, if the coefficient data A _n is composed of 8 bits, the slope accuracy of the gamma characteristic curve can be adjusted up to 1/256 (= 1/2 ⁸ ). .

At this time, if the coefficient data A _n is given as 129 / (256 × 8) (= 16.125 / 256), the data input to the real multiplier 50 is represented as 0001 0000 ₂ with the lower 3 bits rounded off. 16/256 corresponds to the roundoff error from the actual slope. Accordingly, the result of the calculation performed by the multiplier is that the rounding error increases as the coefficient data A _n approaches zero.

3 shows the basic pattern of the energy distribution curve of the video signal in the backlight mode, and FIG. 4 shows the gamma characteristic curve for the backlight compensation used in the video signal processing of FIG.

As shown in FIG. 3, the energy of the image signal in the backlight mode is largely divided into a low level (L) and a high level (H), and in this case, when the gamma correction is performed using a general gamma characteristic curve, the high level ( Processing of the video signal corresponding to H) is not performed properly. Therefore, the gamma characteristic curve used in the backlight mode changes as the slope of the curve is divided into two parts.

Therefore, when gamma correction is performed using the conventional gamma correction device of FIG. 1, as shown in FIG. 4, the offset data B _n may have a negative value according to the value of the coefficient data A _n in the same section. In this case, there is a problem that the implementation of signal processing becomes complicated and the scale of hardware for signal processing increases.

On the other hand, in the case of a liquid crystal display (LCD) device which is recently used as a display device, since the input and output signal characteristics are linear, in order to reproduce a desired screen, the gamma corrected digital image signal data input to the image receiving device is reversed as shown in FIG. 5. There may be times when you need to perform de-gamma correction.

In the case of inverse gamma correction using the gamma correction device of FIG. 1, the offset data B _n always has a negative value as shown in FIG. 5, and in particular, as the value of the coefficient data A _n increases, the offset data B _Since the value of _n becomes very large in the negative direction, it cannot be expressed by a conventional gamma correction device having a limited number of bits, and thus a signal processing becomes impossible.

In order to solve the above problems, an object of the present invention is to provide a gamma correction device and a gamma correction method for digital image signal data that can reduce the round-off error generated in the multiplier to increase the accuracy of signal processing in non-linear signal processing It is.

Another object of the present invention is to provide a gamma correction apparatus and a gamma correction method for digital image signal data, which can simplify the implementation of signal processing for gamma correction by preventing generation of offset data having negative values.

1 is a block diagram schematically showing the configuration of a gamma correction apparatus for a conventional digital image signal data;

FIG. 2 is a diagram schematically illustrating a method of approximating a general gamma characteristic curve (Y = X ^γ , γ = 0.45) using a gamma correction apparatus of digital image signal data of FIG. 1;

3 is a diagram showing a basic pattern of an energy distribution curve of digital video signal data of a camcorder in the backlight mode;

4 is a diagram schematically illustrating a method of approximating a gamma characteristic curve for backlight compensation of a camcorder by using the gamma correction apparatus of digital image signal data of FIG. 1;

FIG. 5 is a diagram schematically illustrating a method of approximating a de-gamma characteristic curve using a gamma correction apparatus of digital image signal data of FIG. 1. FIG.

6 is a block diagram schematically showing the configuration of an embodiment of a gamma correction apparatus for digital image signal data according to the present invention;

7 is a block diagram schematically showing the configuration of another embodiment of a gamma correction apparatus for digital video signal data according to the present invention;

FIG. 8 is a diagram schematically illustrating a method of approximating a general gamma characteristic curve (Y = X ^γ , γ = 0.45) using a gamma correction apparatus of digital image signal data of FIG. 7.

9 is a diagram schematically illustrating a method of approximating an inverse gamma characteristic curve using a gamma correction apparatus of digital image signal data of FIG. 7;

FIG. 10 is a block diagram schematically illustrating a configuration of a gamma correction apparatus of digital image signal data in which a digital logic circuit of the gamma correction apparatus of digital image signal data of FIGS. 6 and 7 is replaced with one microprocess; FIG.

11 is a flowchart schematically showing an embodiment of a gamma correction method of digital image signal data according to the present invention;

12 is a flowchart schematically illustrating still another embodiment of a gamma correction method of digital image signal data according to the present invention.

Explanation of symbols used in the main part of the drawing

130: encoder 140: memory

150: multiplier 160: adder

170: microcomputer 180: division shifter

190: subtractor

In order to achieve the above object, a gamma correction apparatus for digital video signal data according to the present invention is characterized by receiving a predetermined code signal corresponding to a section to which a level of digital video signal data is applied by receiving digital video signal data input from the outside. The encoder to output, the offset data of the approximate straight line for each section, the coefficient data and the amplification coefficient of the approximate straight line for each section, in a predetermined position, and in the section to which the level of the digital video signal data belongs according to the code signal output from the encoder. A storage means for outputting the offset data, the coefficient data and the amplification coefficient of the multiplier, a multiplier for multiplying the coefficient data input from the digital video signal data and the storage means and outputting the result, and the result output from the multiplier means Divide the amplification coefficient by the original And an adder for outputting gamma-corrected digital image signal data by adding the output from the divider and the offset data input from the storage means.

Preferably, in the gamma correction apparatus for digital video signal data according to the present invention, the storage means stores the amplification index m instead of the amplification coefficient N and outputs the amplification index according to a predetermined code signal output from the encoder. The gamma correction device according to the present invention may further include a shift means for receiving an amplification index m from the storage means and reducing the result output from the multiplier to 1/2 ^m and applying the result to the adder.

More preferably, the gamma correction apparatus for digital image signal data according to the present invention further includes a subtractor which subtracts a section start point of each section from the digital image signal data input from the outside and outputs the result to the multiplier, the multiplier The result is multiplied by the count data input from the storage means, and the result is output. The offset data applied to the adder is given as an output value at the start point of each section to prevent the offset data from becoming a negative value.

In addition, in order to achieve the above object, the gamma correction method of digital image signal data according to the present invention divides the set gamma characteristic curve into a plurality of sections, section start point for each section, amplification coefficient N for each section, and approximation for each section. A first step of setting coefficient data amplified by N times the slope of a straight line and offset data which is an output value of an approximate straight line at each section starting point of each section; a second step of determining whether digital image signal data is input; As a result of the determination in step 2, when the digital video signal data is input, the third step of determining a section to which the level of the digital video signal data belongs, and subtracting the section start point of the section to which the level of the digital video signal data belongs from the digital video signal data A fourth step of generating S, multiplying the coefficient data of the section to which the digital video signal data belongs by S and Z A fifth step of generating, a sixth step of generating W by dividing Z by the amplification coefficient N of a section to which the digital video signal data belongs, and gamma correction by adding offset data of a section to which the digital video signal data belongs to W. And a seventh step of outputting digital image signal data.

Hereinafter, a preferred embodiment of a gamma correction apparatus for digital image signal data according to the present invention will be described in detail with reference to the accompanying drawings.

6 is a block diagram schematically illustrating a configuration of a gamma correction apparatus for digital image signal data according to the present invention.

As shown in FIG. 1, an image signal input through the image sensor 10 is converted into digital image signal data X by the A / D converter 20 and then applied to the encoder 130 and the microcomputer 170.

The microcomputer 170 automatically analyzes the energy distribution of the image signal by dividing the digital image signal data into regular intervals, for example, by one frame unit, using a known signal processing algorithm, or according to a user's operation mode selection. The gamma characteristic curve optimized for processing is determined, and accordingly, the gamma characteristic curve is divided into predetermined sections with respect to the level of the input signal, and then the section boundary point X _n and the slope A _n of the approximate straight line and the Y intercept of the approximate straight line for each section. In offset data B _n are defined and these data are output to the encoder 130 and the memory 140.

In this case, the width and number of the divided sections are preferably determined according to the curvature of the gamma characteristic curve. That is, more accurate signal processing can be realized by making the width of the section of the section having the large curvature smaller than the width of the section of the section having the small curvature.

In addition, the microcomputer 170 amplifies the slope A _n of the approximate straight line applied to the multiplier 150 to minimize the rounding error in the multiplier 150. Is an integer greater than or equal to 0), and the coefficient data A _n ′ is defined by multiplying the approximate straight slope A _n by 2 ^m as shown in the following equation.

At this time, it is preferable to set the amplification index m such that the count data A _n ′ exceeds the limited number of bits so that no overflow occurs.

For example, when coefficient data is set to 8 bits, coefficient data A _n ′ generally has a value from 0 to 255/256, that is, 0000 0000 ₂ to 1111 1111 _{2 in} binary code.

If the n th coefficient data A _n ′ is given as 129 / (256 × 8) (= 16.125 / 256), the amplification index set by the microcomputer 170 so that no overflow occurs is m = 3, where the memory The coefficient data A _n ′ stored at 140 is amplified by 2 ³ times the actual approximate slope, that is, 1000 000 _{1 2} shifted by 3 bits to the left, thereby minimizing rounding errors.

The encoder 130 receives the section boundary point X _n set by the microcomputer 170 and compares the section boundary point X _n with the digital image signal data X applied from the A / D converter 20 to the level of the digital image signal data. Accordingly, a predetermined code signal, for example, is converted into a specific address of the preset memory 140 and applied to the memory 140.

The memory 140 stores the approximate linear coefficient data A _n ′, the offset data B _n , and the amplification index m at an address of the preset memory 140 applied from the microcomputer 170, and stores the coefficient data A _n ′ from the encoder 130. Approximate linear coefficient data A _n ′, offset data B _n , and amplification index m are applied to the multiplier 150, the adder 160, and the divider shifter 180 according to the output code signal. do.

The multiplier 150 multiplies the digital image signal data X input from the A / D converter 20 by the coefficient data A _n ′ input from the memory 140 and divides the result (A _n ′ × X) by the division shifter 180. Output to At this time, the result output from the multiplier 150 is amplified by 2 ^m times and amplified by 2 ^m times the actual value by the input coefficient data A _n ′, and thus the rounding error of the multiplier 150 is reduced by 1/2 ^m . Done.

In order to obtain a desired signal processing result by the gamma correction device according to the present invention, it is necessary to amplify by 2 ^m times and divide the result output from the multiplier 150 by 2 ^m again. Therefore, a divider is further provided for dividing the result output from the multiplier 150 by 2 ^m . Preferably, the divider is composed of a divider shifter 180 to implement a division operation of 2 ^m even with a simple circuit configuration. Can be.

That is, the division shifter 180 is, for example, a shift register, and receives the amplification index m from the memory 140 and shifts the result output from the multiplier 150 by m-bit to the right. Reduce the output from ½ ^m . For example, if the amplification index m applied from the memory 140 is 3 and the result output from the multiplier 150 is 1 0000 0000 0000 0000 ₂ = 2 ¹⁶ , the operation result in the division shifter 180 is 0 0010 0000 0000 As 0000 ₂ = 2 ¹³ , the result output from the multiplier 150 is divided by 2 ³ .

The adder 160 adds the offset data B _n applied from the memory 140 to the result output from the division shifter 180 and outputs the result as gamma-corrected digital image signal data Y.

In this case, the gamma-corrected digital image signal data Y may be expressed by the following equation.

Next, another embodiment of the gamma correction apparatus according to the present invention which always has positive offset data will be described in detail with reference to FIGS. 7 to 9.

7 is a block diagram schematically showing the configuration of another embodiment of a gamma correction device according to the present invention, and FIG. 8 schematically illustrates a method of approximating a gamma characteristic curve using the gamma correction device of digital image signal data of FIG. 7. FIG. 9 is a diagram schematically illustrating a method of approximating an inverse gamma characteristic curve using a gamma correction apparatus of digital image signal data of FIG. 7.

In FIG. 7, components having the same reference numerals as those of FIG. 6 show the same operational effects as those of FIG. 6, and thus detailed descriptions thereof will be omitted.

The microcomputer 170 determines a gamma characteristic curve optimized for digital image signal data processing of the system, and accordingly, as shown in FIG. 6, the boundary point X _n and the amplification index m and the slope of the approximate straight line are 2 ^{m each.} By defining the coefficient data A _n ′ and the offset data B _n ′, the edge boundary point X _n is applied to the encoder 130, and the memory 140 has the interval starting point X _n−1 , the amplification index m, and the approximate linear coefficient. Outputs data A _n 'and offset data B _n '. At this time, the offset data B _n ′ is defined as an output value at the start point X _n-1 of each section.

The memory 140 stores the section start point X _n-1 and the amplification index m, the approximate linear coefficient data A _n ′ and the offset data B _n ′ for each section applied from the microcomputer 170 at a preset address, A subtractor 190 and dividing the interval start point X _n-1 and the amplification index m, the approximate linear coefficient data A _n ′ and the offset data B _n ′, respectively, in the section to which the digital image signal data belongs according to the code signal output from 130). The shifter 180 is applied to the multiplier 150 and the adder 160.

The subtractor 190 subtracts the section start point X _n-1 applied from the memory 140 from the digital image signal data X input from the A / D converter 20, and then outputs XX _n-1 to the multiplier 150. do.

In this case, when the interval start point X _n-1 of the _nth section {X _n , X _n-1 } is given as 2 ^n-1 , the subtractor 190 may be simply configured as an AND gate. For example, when the digital image signal data X is 40 = 0 0010 1000 ₂ in a system composed of 9 bits, the interval start point X _n-1 applied to the subtractor 190 is given as 32 = 2 ⁵ , and the end gate 1 1101 1111 _2, which is 1's complement of interval start point X _n-1 = 2 ⁵ , is applied to 190, resulting in 40-32 = 8 = 0 0000 1000 ₂ .

The multiplier 150 multiplies the result XX _n-1 applied from the subtractor 190 by the coefficient data A _n ′ input from the memory 140 and divides the result A _n ′ × (XX _n-1 ) by the division shifter ( 180).

An approximation method of the gamma characteristic curve in the gamma correction device of FIG. 7 will be described in more detail with reference to FIG. 8.

In order to obtain an approximated gamma characteristic curve in the gamma correction apparatus according to the present invention, as shown in FIG. 2, after dividing the level of the digital image signal data into a proper number of sections, defining the inclination and offset data of the approximate straight line for each section is performed. need.

In this case, as shown in FIG. 8, the slope of the approximate straight line is represented by the following equation.

Here, X _n-1 , X _n represent the section start point and the section end point in the _nth section {X _n-1 , X _n }, respectively, and Y _n-1 , Y _n are respectively at X _n-1 , X _n The output value of.

On the other hand, the offset data B _n ′ applied from the memory 140 to the adder 160 is not an approximate straight Y-intercept as in the gamma correction apparatus of FIG. 1, but a section of the section to which the digital image signal data belongs, as shown in the following equation. is defined as the output value Y _n-1 at the starting point X _n-1.

B _n = Y _n-1

Accordingly, the gamma corrected digital image signal data Y output from the adder 160 of FIG. 7 may be represented by the following equation, and offset data B _n ′ is always 0 regardless of the slope of the gamma characteristic curve. Has a greater value.

In addition, as shown in FIG. 9, even when the gamma correction apparatus of the digital image signal data according to the present invention is used for the de-gamma correction signal processing, the same as in the conventional gamma correction apparatus of the digital image signal data. There is no problem of negative number generation, and offset data always has a positive value.

On the other hand, although not shown in the drawing as another embodiment of the gamma correction device of the digital image signal data according to the present invention, the gamma correction of the digital image signal data in the gamma correction apparatus of the digital image signal data of Figure 6 or 7 When the gamma characteristic curve for signal processing is set to be fixed, the section boundary point X _n for approximating the gamma characteristic curve, the coefficient data A _n ´ and the offset data B _n ´ for the approximate straight line for each section are processed by the microcomputer. By directly storing the encoder 130 and the memory 140 without going through it, the signal processing speed can be improved without having a separate hardware resource, that is, the microcomputer 170.

Although not shown in the drawings, as a fourth embodiment of the gamma correction apparatus for digital image signal data according to the present invention, the microcomputer 170 in the gamma correction apparatus for digital image signal data in FIG. By defining the slope A _n of the gamma characteristic curve and storing it in the memory 140, the coefficient data is obtained by multiplying the slope A _n of the gamma characteristic curve 2 ^m through a separate multiplying shifter (not shown). It is also possible to apply to the multiplier 150. In this case, the multiplication shifter is configured of, for example, a shifter register, and receives an amplification index m from the memory 140 to move the slope A _n of the gamma characteristic curve input from the memory 140 by m-bit to the left. ) the data entered from the 2 ^m times thereby amplified.

The gamma correction apparatus of the digital image signal data according to the present invention may not only be configured with a digital logic circuit as shown in FIG. 6 or 7 but may also be implemented as a single microprocessor as shown in FIG.

The operation of the gamma correction apparatus for digital image signal data according to the present invention configured as described above will be described in more detail with reference to FIGS. 11 and 12.

11 is a flowchart schematically illustrating an embodiment of a gamma correction method of digital image signal data according to the present invention.

First, the microcomputer 170 is approximate the gamma characteristic curve and each piecewise interval feature points X _n, each section coefficient data of each approximation line A _n ', the offset data of each piecewise approximation line B _n, and each in accordance with the digital video signal Amplification index m for each section is set (S100).

In more detail, when the digital video signal X _o is input from the A / D converter 20, the microcomputer 170 analyzes the input digital video signal data X _o to perform image signal processing. The gamma characteristic curve is determined by dividing it into a plurality of sections, and the section boundary point X _n for each section, the slope of the approximate straight line A _n , the offset data B _n , which is the Y intercept of the approximate straight line for each section, and the approximation for each section. The amplification index m for each section is set according to the slope of the straight line (S120). Next, the microcomputer 170 amplifies the slope of the approximate straight line by 2 ^m times to obtain coefficient data A _n ′ of the approximate straight line for each section (S130).

When the coefficient data A _n ′, the offset data B _n, and the amplification index m of each section of the gamma characteristic curve approximated by step 100 are determined, the microprocessor 300 inputs the digital image signal data X for image signal processing. It is determined whether or not (S200).

If it is determined in step S200 that the digital image signal data X is input, the microprocessor 300 determines a section n to which the digital image signal data X belongs (S300).

The determining of the section n to which the digital image signal data X belongs (S300) may be performed by the following detailed process.

First, one variable k is selected and set to an initial value, for example, k = 1 (S310), and then the digital image signal data X is compared with the end point X _k of the k-th section (S320). As a result of the comparison, if the digital video signal data is larger than the end point X _k of the k-th section, the variable k and the maximum section value n _max are compared (S330). If the variable k is smaller than the maximum section value n _max , the value k is counted up. If the variable k is greater than or equal to the maximum interval value n _max , the stored value of the variable k, that is, the maximum interval value n _max , is equal to the interval value n of the section to which the digital image signal data X belongs. Set to (S350). Here, the maximum interval value n _max is given by the same value as the number of divided sections of the gamma characteristic curve.

On the other hand, if the digital video signal data is less than or equal to the section endpoint X _k of the k-th section in step S320, the current stored value of the variable k is set to the section value n of the section to which the digital video signal data X belongs (S350).

If the section value n of the section to which the digital video signal data X belongs is determined by step S300, the coefficient data A _n ′ of the section to which the digital video signal data X belongs is multiplied by the digital video signal data X (the result is referred to as Z below). (S400). Here, the coefficient data A _n ′ is a value obtained by amplifying an approximate linear slope by 2 ^m times, so that the rounding error in the multiplier 150 is reduced by 1/2 ^m .

Next, to obtain a desired signal, Z generated by step S400 is divided by an amplification value of 2 ^m in coefficient data A _n '(the result is referred to as W below) (S500), preferably a binary code. The value Z generated by step S400 is reduced to 1/2 ^m by shifting the variable Z to the right by m-bit.

After performing step S500, gamma corrected digital image signal data Y is generated by adding offset data B _n of a section to which digital image signal data belongs to W (S600).

12 is a flowchart schematically showing another embodiment of a gamma correction method of digital image signal data according to the present invention.

The microcomputer 170 calculates the section boundary point X _n of each section of the approximated gamma characteristic curve, the coefficient data A _n ′ of the approximate straight line for each section, the offset data B _n ′ of the approximate straight line for each section, and the amplification index m for each section. Set. In this case, as shown in FIG. 8, the offset data B _n ′ of the approximate straight line for each section set by the microcomputer 170 is given as an output value of the gamma characteristic curve at the section start point X _n-1 for each section. Therefore, the offset data B _n ′ always have a positive value regardless of the slope of the gamma characteristic curve.

The gamma correction apparatus of FIG. 7 determines the section value n of the section to which the digital video signal data X belongs (S1300), and then subtracts the section start point X _n-1 of the section to which the digital video signal data X belongs from the digital video signal data X. (The result is called S below.) (S1360).

After performing step S1360, S is multiplied by the coefficient data, the result is stored in Z (S1400), and Z is further divided into 2 ^m and stored in W (S1500).

The gamma-corrected digital image signal data Y is generated by adding offset data B _n ′ in the section to which the digital image signal data X belongs to the variable W generated in step S1500 (S1600).

On the other hand, in the gamma correction device and the gamma correction method of the digital image signal data according to the present invention, the above-mentioned amplification coefficient of the slope of the approximate straight line may be replaced by any positive number N or more instead of 2 ^m . In this case, hardware resources used to construct a gamma correction apparatus for digital video signal data are required more than when the amplification value is 2 ^m , but the accuracy of gamma correction signal processing can be further improved.

As described above, when the amplification coefficient is replaced with an arbitrary positive number N or more, the data input to the memory 140 in the microcomputer 170 becomes the amplification coefficient N for each section instead of the amplification index m for each section, and the present invention The division shifter 180 of the gamma correction device according to the present invention is replaced with a known divider for dividing the result output from the multiplier 150 by N.

As described above, according to the gamma correction device and the gamma correction method of digital image signal data according to the present invention, the round-off error in the multiplier is reduced by amplifying coefficient data input to the multiplier and then reducing the calculation result again. This increases the accuracy of the gamma correction signal processing.

In addition, since the offset data input to the adder is always a positive value, there is an effect of saving hardware resources, and even when de-gamma correction (Gamma correction) of the digital image signal data according to the present invention without changing the hardware The effect can be used as it is.

Preferred embodiments described in the specification of the present invention are illustrative and should not be interpreted in a limiting sense. Further, the scope of the present invention is not limited to the gamma correction device and the gamma correction method for signal processing according to the gamma characteristic curve, and other nonlinear video signal processing devices and video signals that can be applied without changing the core of the present invention. It should also be interpreted as being insane.

Claims (18)

The gamma characteristic curve of the input signal to the output signal is divided into a plurality of sections according to the level of the input signal, and digitally obtained according to the approximated gamma characteristic curve obtained by successively connecting a series of approximation lines corresponding to the gamma characteristic curve for each section. A gamma correction apparatus for digital video signal data for gamma correction of video signal data; An encoder which receives digital video signal data input from an external device and outputs a predetermined code signal corresponding to a section to which the level of the digital video signal data belongs; The amplification coefficient N for each section, the coefficient data for each section amplified by N times the slope of the approximate straight line for each section, and the offset data which is the Y-intercept of the approximate straight line for each section are stored in a predetermined position, and the code outputted from the encoder Storage means for outputting an amplification coefficient N, coefficient data and offset data of a section to which the level of the digital video signal data belongs in accordance with the signal; A multiplier for multiplying the digital video signal data by the coefficient data input from the storage means and outputting the result; A divider for dividing the result output from the multiplier by the amplification coefficient N input from the storage means and outputting the result; And And an adder for outputting gamma-corrected digital video signal data by adding the result output from the divider and the offset data input from the storage means. The apparatus of claim 1, wherein the gamma correction apparatus for digital image signal data comprises: To define the gamma characteristic curve, the slope of the approximate straight line for each section and the offset data of the approximate straight line for each section are set, and the amplification coefficient N for each section and the approximate straight line for each section are set according to the slope of the approximate straight line for each section. And a microcomputer for setting the coefficient data amplified by N times the slope and outputting the amplification coefficient N, the coefficient data and the offset data for each section to the storage means. The method according to claim 1 or 2, wherein the amplification coefficient N; A gamma correction device for digital video signal data, characterized in that 2 ^m (m is an arbitrary integer equal to or greater than 0). 4. The apparatus of claim 3, wherein the divider; And a shift means for receiving an amplification index m from the storage means and shifting the result input from the multiplier to the right by m bits. The gamma characteristic curve of the input signal to the output signal is divided into a plurality of sections according to the level of the input signal, and digitally obtained according to the approximated gamma characteristic curve obtained by successively connecting a series of approximation lines corresponding to the gamma characteristic curve for each section. A gamma correction apparatus for digital video signal data for gamma correction of video signal data; An encoder which receives digital video signal data input from the outside and outputs a predetermined code signal according to the level of the digital video signal data; The offset data of each section's approximate straight line given as the output data from the section start point for each section, the amplification coefficient N for each section, N times the slope of the approximation straight line for each section, and the output value from the section start point for each section Storage means for storing the interval start point, the amplification coefficient N, the coefficient data, and the offset data of the section to which the level of the digital video signal data belongs according to the code signal output from the encoder; A subtractor which receives the digital image signal data and subtracts a section start point output from the storage means from the digital image signal data and outputs the result; A multiplier for multiplying the result input from the subtractor by the coefficient data input from the storage means and outputting the result; A divider for dividing the result output from the multiplier by the amplification coefficient N input from the storage means and outputting the result; And And an adder for outputting gamma-corrected digital video signal data by adding the result output from the divider and the offset data input from the storage means. The apparatus of claim 5, wherein the gamma correction apparatus of the digital image signal data comprises: To define the gamma characteristic curve, the section starting point for each section, the slope of the approximate straight line for each section, and the offset data of the approximate straight line for each section are set, and the amplification coefficient N for each section is calculated according to the slope of the approximate straight line for each section. And further comprising a microcomputer for setting the coefficient data amplified by N times the slope of the approximate straight line in the section and outputting the section starting point for each section, the amplification coefficient N for each section, and the coefficient data of the approximate straight line to the storage means. A gamma correction device for digital video signal data, characterized in that. The method according to claim 5 or 6, wherein the amplification coefficient N is; A gamma correction device for digital video signal data, characterized in that 2 ^m (m is an arbitrary integer equal to or greater than 0). 8. The apparatus of claim 7, wherein the divider; And a shift means for receiving an amplification index m from the storage means and shifting the result input from the multiplier to the right by m bits. The method of claim 5 or 6, wherein the interval start point is; A gamma correction device for digital video signal data, characterized in that 2 ⁿ (n is an integer greater than or equal to 0). The method of claim 9, The subtractor; And Gate, And a complement of one of the section starting point is applied from the storage means to the subtractor. The gamma characteristic curve of the input signal to the output signal is divided into a plurality of sections according to the level of the input signal, and digitally obtained according to the approximated gamma characteristic curve obtained by successively connecting a series of approximation lines corresponding to the gamma characteristic curve for each section. A gamma correction method of digital video signal data for gamma correction of video signal data: Coefficient data obtained by dividing the set gamma characteristic curve into a plurality of sections, amplifying the section boundary point for each section, the amplification coefficient N for each section, and N times the slope of the approximation straight line for each section, and the offset which is the Y intercept of the approximate straight line for each section A first step of setting data; A second step of determining whether digital image signal data is input; A third step of determining a section to which the level of the digital video signal data belongs when the digital video signal data is input as a result of the determination in the second step; A fourth step of generating Z by multiplying the coefficient data of the section to which the digital video signal data belongs by the digital video signal data; A fifth step of generating W by dividing Z by the amplification coefficient N of a section to which the digital image signal data belongs; And a sixth step of outputting gamma-corrected digital video signal data by adding offset data of a section to which the digital video signal data belongs to W. 6. The method of claim 11, wherein the third step; Setting the variable k to an initial value; Comparing the digital image signal data with a section endpoint X _k of a k-th section; Comparing the variable k with a maximum interval value n _max when the digital image signal data is larger than a section endpoint X _k of a k-th section; If the variable k is smaller than the maximum interval value n _max , _{returning the} variable k and then comparing the digital video signal data with the interval endpoint X _k of the _kth section; And setting the variable k to a section value to which the digital video signal data belongs when the digital video signal data is not larger than the section endpoint X _k of the k-th section or the variable k is greater than or equal to the maximum section value n _max. A gamma correction method of digital video signal data, characterized in that. The method of claim 11 or 12, The amplification coefficient is a gamma correction method of the digital image signal data, characterized in that 2 ^m (m is an integer of 0 or more). The method of claim 13, wherein the fifth step; A gamma correction method of digital image signal data, characterized by shifting the variable Z right by m-bit. The gamma characteristic curve of the input signal to the output signal is divided into a plurality of sections according to the level of the input signal, and digitally obtained according to the approximated gamma characteristic curve obtained by successively connecting a series of approximation lines corresponding to the gamma characteristic curve for each section. A gamma correction method of digital video signal data for gamma correction of video signal data; The gamma characteristic curve is divided into a plurality of sections, and the coefficient data is amplified by N times the interval starting point for each section, the amplification coefficient N for each section, and the slope of the approximate straight line for each section, and the approximate straight line at the section starting point for each section. A first step of setting offset data as an output value; A second step of determining whether digital image signal data is input; A third step of determining a section to which the level of the digital video signal data belongs when the digital video signal data is input as a result of the determination in the second step; Generating an S by subtracting a start point of a section from which the level of the digital video signal data belongs to the digital video signal data; A fifth step of generating Z by multiplying S by coefficient data of a section to which the digital image signal data belongs; A sixth step of generating W by dividing Z by the amplification coefficient N of a section to which the digital image signal data belongs; And a seventh step of outputting gamma-corrected digital video signal data by adding W data with offset data of a section to which the digital video signal data belongs. The method of claim 15, wherein the third step; Setting the variable k to an initial value; Comparing the digital image signal data with a section endpoint X _k of a k-th section; Comparing the variable k with a maximum interval value n _max when the digital image signal data is larger than a section endpoint X _k of a k-th section; If the variable k is smaller than the maximum interval value n _max , _{returning the} variable k and then comparing the digital video signal data with the interval endpoint X _k of the _kth section; And setting the variable k to a section value n to which the digital video signal data belongs when the digital video signal data is not larger than the section endpoint X _{k of the kth} section or the variable k is greater than or equal to the maximum section value n _max. A gamma correction method of digital video signal data, characterized in that the. The method according to claim 15 or 16, The amplification coefficient is a gamma correction method of the digital image signal data, characterized in that 2 ^m (m is an integer of 0 or more). 18. The method of claim 17, wherein the sixth step is performed; And gamma correcting the Z to the right by m-bit.