TWI414177B - Apparatus and method for gamma correction - Google Patents

Abstract

Apparatus and method for gamma correction are disclosed. An adjustable blending unit is utilized for adjustably blending a linear gamma function with a nonlinear gamma function, thereby resulting in an adjustable gamma curve. The nonlinear gamma function is adjustable by a blending parameter such that distance of the gamma curve to linear gamma curve may be changed.

Description

Gamma correction device and method

The present invention relates to gamma correction, particularly gamma correction using an adjustable and adaptable curve function.

Most display systems have a non-linear display characteristic called gamma response that causes the display system to display a brightness that is not perfectly proportional to the input voltage. In view of this gamma characteristic, the image signal is usually compensated by the gamma curve before being displayed, so that the nonlinear characteristics of the display system are reversely compensated.

The lookup table method is one of the common methods of traditional gamma correction. However, this method of looking up requires a considerable amount of memory space, and it takes a lot of read cycles to read data from the memory. Piecewise linear approximation is another common way of traditional gamma correction. However, this approach requires a lot of registers to store the end points of the segments and is prone to approximation errors.

Therefore, there is a need for a quick and easy way to perform gamma correction.

In view of the above, one of the objects of the present invention is to provide a fast and simple gamma correction method. The calculations required for such gamma correction and its gamma curve are much less than for conventional gamma correction methods. Furthermore, the user can also easily scale the shape of the gamma curve and adjust its strength.

In accordance with an embodiment of the invention, an adjustable mixing unit is used to mix the linear gamma function with the nonlinear gamma function, thus forming an adjustable gamma curve. The nonlinear gamma function can be adjusted by mixing parameters such that the distance from the gamma curve to the linear gamma curve is changed. The gamma curve can also be adjusted by the intensity parameter such that the curvature of the gamma curve is changed.

The block diagram of the first figure shows a gamma correction device 100 according to an embodiment of the present invention, and the second diagram shows an embodiment of the present invention. Gamma correction method 200. The apparatus 100 and method 200 of the present embodiment are used to compensate for nonlinear characteristics of a display system such as a liquid crystal display. However, the present invention is also applicable to other systems. For example, the gamma correction disclosed in the embodiments of the present invention can also be directly or modified to correct the nonlinear response of the photo sensor. In addition, the present embodiment uses 8-bit to represent the luminance value, so there are a total of 256 gray levels (i.e., 0 to 255). However, other bit numbers can also be used depending on the specific system design requirements.

In the present embodiment, the gamma correction curve (or conversion function) is defined as follows: Y'=(255+a)*Y/(a+Y) (1) Y"=(Y'*(255-Y)+Y ² )/255 ( 2) Y'''=Y+(Y"-Y)*b (3) a=round(avgBrightness*p) (4) where Y represents the luminance value (or luma value) of the input pixel, and Y' represents the intermediate output. Value, Y" represents the output value of the base gamma curve, Y''' represents the luminance value of the output pixel, p is the parameter defining the gamma correction intensity, and b is the definition of the gamma curve to the linear gamma curve The parameter of closeness.

The avgBrightness in the equation (4) represents the average luminance value of the current image. In this embodiment, in step 20 (second diagram), the pixels of the entire image frame or the image window portion to be gamma corrected are obtained by an adaptable luminance value unit 10 (first image). Average brightness value. In this specification, the term "unit" can be used to refer to a circuit, a program segment, or a combination thereof. The average brightness value is influenced by the brightness value "a" to affect the output value Y' of the formula (1), and further affects Y" of the formula (2) and Y"' of the formula (3). The apparatus 100 and the method 200 may The adaptor automatically changes its gamma correction for varying average brightness values. This adaptability is particularly useful when the device 100 is input images of different average brightness from different imaging devices.

The luminance value "a" is further adjusted by steps 21 to 22. Wherein, in step 21, when it is necessary to adjust the gamma correction intensity, the intensity parameter p is obtained in step 22 or input by the user, and transmitted to the adaptable brightness value unit 10. In the present embodiment, the average luminance value (avgBrightness) is multiplied by the intensity parameter p using equation (4). The operator "round" in equation (4) performs a mathematical rounding operation. However, if the device 100 is a non-integer system, the rounding operation can be omitted. The effect of the intensity parameter p on the gamma correction will be detailed later.

The Y" function in equation (2) represents a base gamma curve (steps 23 and 12), which corresponds to the gamma curve of b = 1 in the third figure. In this embodiment, the basic gamma curve is Second-order functions. However, the basic gamma curve can also be represented by higher order functions.

The Y'' function in equation (3) represents a general gamma curve which is combined or blended by a linear portion Y and a nonlinear portion (Y"-Y). A mixture of functions Y''' Step 25) multiplies the non-linear portion (Y"-Y) by a mixing parameter b, which can be input (step 24) by the user into the adjustable mixing unit 14. When b=1, the general gamma curve Y''' becomes the basic gamma curve Y"; when b=0, the general gamma curve Y''' becomes a linear gamma curve. As shown in the third figure, gamma The distance from the curve Y''' (b≠0) to the linear gamma curve (b=0, that is, without any gamma correction) increases with the increase of the mixing parameter b, and vice versa. The third graph also shows that each gamma curve converges to both ends (ie, 0 and 255 in the legend).

As previously mentioned, the basic gamma curve is a function of the luminance value "a", and when the intensity adjustment is selected, the luminance value "a" is again a function of the intensity parameter p. The fourth graph shows the gamma curves corresponding to the various intensity parameters p. The curvature of the Gamma curve Y''' increases as the intensity parameter p decreases. The curvature decreases as the intensity parameter p increases. In the present embodiment, the parameter p of less than 1 makes the gamma correction become more aggressive, while the parameter p of more than 1 makes the gamma correction less robust.

Accordingly, embodiments of the present invention provide an apparatus and method for performing gamma correction quickly and easily. The amount of calculation required for the gamma correction and its gamma curve disclosed in the embodiments of the present invention is much less than that of the conventional gamma correction method. Furthermore, the user can conveniently scale and adjust the intensity of the gamma curve. In addition, in the present embodiment, the use of a single 6-bit register is sufficient to simultaneously store the mixing parameter b and the intensity parameter p. The apparatus and method of an embodiment of the present invention adaptably adjusts its gamma correction for varying average brightness values.

The above description is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; all other equivalent changes or modifications which are not departing from the spirit of the invention should be included in the following Within the scope of the patent application.

100‧‧‧gamma correction device

10‧‧‧adaptable brightness value unit

12‧‧‧Basic gamma curve

14‧‧‧Adjustable mixing

200‧‧‧gamma correction method

20-25‧‧‧Steps for gamma correction method

The block diagram of the first figure shows a gamma correction device according to one embodiment of the present invention.

The second figure shows the gamma correction method of the embodiment of the present invention.

The third graph shows the gamma curve corresponding to the various mixing parameters.

The fourth graph shows the gamma curves corresponding to the various intensity parameters.

100‧‧‧gamma correction device

10‧‧‧adaptable brightness value unit

12‧‧‧Basic gamma curve

14‧‧‧Adjustable mixing

Claims (16)

A gamma correction device includes an adjustable mixing unit that combines a linear gamma function with a nonlinear gamma function to form an adjustable gamma curve; wherein the nonlinear gamma function includes a defined basic gamma The difference between the basic gamma function of the curve and the linear gamma function, and the basic gamma function described above is: Y" = (Y' * (255 - Y) + Y ² ) / 255 where Y" represents the output of the basic gamma curve Value, Y represents the luminance value of the input pixel, and Y' represents the intermediate output value, which is defined as: Y'=(255+a)*Y/(a+Y) where a=round(avgBrightness*p), avgBrightness Represents the average brightness value of the image, round is the mathematical rounding operation, and p represents the parameter of the gamma correction intensity. The gamma correction device of claim 1, wherein the nonlinear gamma function is adjustable. The gamma correction device of claim 2, wherein the nonlinear gamma function is adjusted by mixing parameters, such that The distance from the gamma curve to the linear gamma curve is varied, where the linear gamma curve represents a function that is not subject to any gamma correction. The gamma correction device of claim 1, wherein the basic gamma function is a second order function. The gamma correction device of claim 1, wherein the basic gamma function is a function of an average brightness value of the image. The gamma correction device of claim 5, wherein the image average brightness value is adjustable. The gamma correction device of claim 6, wherein the image average brightness value is adjusted by an intensity parameter such that the curvature of the gamma curve is changed. The gamma correction device according to claim 1, wherein the gamma curve can be expressed as: Y'''=Y+(Y"-Y)*b, wherein Y''' represents a brightness value of the output pixel, And b is a parameter defining the closeness of the gamma curve to the linear gamma curve, The linear gamma curve represents a function that is not subject to any gamma correction; wherein Y represents the linear gamma function and (Y"-Y) represents the nonlinear gamma function. A gamma correction method includes mixing a linear gamma function and a nonlinear gamma function to form an adjustable gamma curve; wherein the nonlinear gamma function includes a basic gamma function defining a basic gamma curve The difference between the linear gamma functions, and the basic gamma function described above is: Y" = (Y' * (255 - Y) + Y ² ) / 255 where Y" represents the output value of the basic gamma curve and Y represents the input pixel The brightness value, and Y' represents the intermediate output value, which is defined as: Y'=(255+a)*Y/(a+Y) where a=round(avgBrightness*p), avgBrightness represents the average brightness value of the image , round is a mathematical rounding operation, and p represents a parameter of the gamma correction intensity. The gamma correction method according to claim 9, wherein the nonlinear gamma function is adjustable. For example, the gamma correction method described in claim 10 further includes a step of adjusting the nonlinear gamma function by mixing parameters such that the distance from the gamma curve to the linear gamma curve is changed, wherein the linear gamma curve represents an un Subject to any gamma correction. The gamma correction method according to claim 9, wherein the basic gamma function is a second order function. The gamma correction method according to claim 9, wherein the basic gamma function is a function of an average brightness value of the image. The gamma correction method according to claim 13, wherein the image average brightness value is adjustable. For example, the gamma correction method described in claim 14 further includes a step of adjusting the average brightness value of the image by an intensity parameter such that the curvature of the gamma curve is changed. The gamma correction method according to claim 9, wherein the gamma curve can be expressed as: Y'''=Y+(Y"-Y)*b, wherein Y''' represents a luminance value of the output pixel, And b is a parameter defining a closeness of the gamma curve to a linear gamma curve, wherein the linear gamma curve represents a function that is not subject to any gamma correction; wherein Y represents the linear gamma function, and (Y"-Y ) represents the nonlinear gamma function.