Help for GAMMA

PURPOSE:

Perform gamma correction to the input image. The program provides two gamma 
correction modes: sRGB and simple. sRGB gamma correction mode is implemented 
based on the specification of sRGB, and simple gamma correction mode is 
implemented based on pure exponential function. See method section for more 
details. The input is a 1-band or 3-band image in BYTE, HALF, and REAL (not 
fully tested) format. The output is a 1-band or 3-band image in BYTE format. 
The exponent value is required for simple gamma correction.

EXECUTION:

1) sRGB gamma correction:
   GAMMA INP=linear_srgb.vic OUT=srgb.vic -srgb

2) Simple gamma correction:
   GAMMA INP=linear_wrgb.vic OUT=wrgb.vic

METHOD:
1) sRGB gamma correction:
This is implemented based on the specification of sRGB. The constant values 
used are all defined in the specification. The detailed algorithm is shown
below. The srgb gamma correction requires a 3-band input as it is not 
meaningful to be applied on 1-band images.

    If RL, GL, BL are less than or equal to 0.0031308
        R = 12.92 * RL
        G = 12.92 * GL
        B = 12.92 * BL

    If RL, GL, BL are greater than 0.0031308
        R = 1.055 * RL^(1/2.4) - 0.055
        G = 1.055 * GL^(1/2.4) - 0.055 
        B = 1.055 * BL^(1/2.4) - 0.055

    where RL, GL, and BL are linear RGB values. 

2) simple gamma correction:
This is implemented based on the pure exponential functionis listed below.

    If 1-band input
        I = I^exponent
 
    If 3-band input
        R = RL^exponent
        G = GL^exponent
        B = BL^exponent

    where I is the intensity value; RL, GL, and BL are linear RGB values.



HISTORY:
28-Mar-2018  Steven Lu  Initial delivery
COGNIZANT PROGRAMMER: