Multiplying and adding images with CImg In C++

Question

Hello

I am trying to find C in the following function in CImg

C=B*L+(1-B)S

Where C, L and S are all RGB images of the same size (and B is a single channel grayscale matte)

I cannot figure out how to loop over the pixels. I've seen code like:

cimg_forXYZ(S,x,y,z) {... }

But I have never see than kind of syntax before, could it be a macro?

Any suggestions are welcome.

Answer 1

If you look into the CImg header, you'll see that that code is, in fact, a macro that thunks down into:

#define cimg_forXY(img,x,y)       cimg_forY(img,y) cimg_forX(img,x)
#define cimg_forX(img,x)          for (int x=0; x<(int)((img).width); ++x)
#define cimg_forY(img,y)          for (int y=0; y<(int)((img).height); ++y)
#define cimg_forZ(img,z)          for (int z=0; z<(int)((img).depth); ++z)
#define cimg_forXYZ(img,x,y,z) cimg_forZ(img,z) cimg_forXY(img,x,y)

Which means that you will have the following loops:

for (int z=0; z<(int)((img).depth); ++z)
    for (int y=0; y<(int)((img).height); ++y)
        for (int x=0; x<(int)((img).width); ++x) {

}

So, now, what you probably want to do is reference either the x, y, and z coordinates, or better, the pointer into the data as you step through, like

cimg_library::CImg<float> image;
//assign, etc
float* ptr = image->ptr();
cimg_forXYZ(S, x, y, z){
    *ptr = *ptr + 10;
    ++ptr;
}

I encourage you to read the CImg header; it's quite elegant. You'll get a lot of functionality 'for free'.