Gamma correction gamma calibration and MATLAB implementation

Matlab built-in implementation: Imadjust
Gamma Correction
Gamma correction formula:. ^ (gamma) or. ^ (1/gamma)?

The nonlinear operation used to adjust the illumination intensity of the image is as follows:

Vout=avγin V_{\text{out}}=av_{\text{in}}^\gamma

Vin V_{\text{in}}: Nonnegative real values, such as image pixels, a A: a constant, usually with a value of 1, the input and output range is generally [0, 1];
Γ<1 \gamma: Light intensity is stronger, called Gamma compressionγ>1 \gamma > 1: Light intensity becomes weaker, called gamma expansion

function gammacorrection (name, a, gamma)
 r = imread (name);
 R=im2double (r);                
 R=rgb2gray (r);                % when the input is a grayscale image, delete the sentence;
 s = A * (R. ^ gamma);
 Subplot (1, 2, 1), Imshow (R), title (' Original ');
 Subplot (1, 2, 2), Imshow (s), title (sprintf (' Gamma:%0.1f ', gamma));
End