title: RGB pixel transparency
body: <p>I am combining two RGB images, pixel by pixel, each of different sizes, while combining them I'd like the one that is on top, which is smaller in size to be transparent regarding two the bigger one in the background, like a see-through. What processing should I do? Cause right now..merging the images resumes just to replacing pixels. How can I achieve this transparency? I'm using c++.</p>