Question

I tried to do some simple gamma correction on an image. At first, I tried using Matlab then I apply it on opencv. But I get different result. Below is some of the code. Where does the code goes wrong?

In matlab:

for i=1:r;
    for j=1:c;
       imout(i,j)=constant_value*power(img_double(i,j),0.04);
    end
 end

In OpenCV:

for(int y=0; y<height; y++){
   for(int x=0; x<width; x++)
   {
        dataNew[y*stepNew+x] = constant_value*pow(dataNew[y*stepNew+x], 0.04);
   }
}

Where the image is an unsigned 8 bit, 1 channel image. Which part that I miss?

Answer 1

My guess is that you forgot to scale your image data in OpenCV to the interval [0,1]. In Matlab im2double does this for you automatically.
So for an 8 bit image something like this should work:

dataNew[y*stepNew+x] = 255 * constant_value*pow(dataNew[y*stepNew+x]/255.0, 0.04);