Courtesy of my optometrist, I now have images of my retinas. However, the images are a bit dark. I have RGB values for each pixel. In this setting, is brightening the image equivalent to increasing each of the RGB values slightly (toward white)?
That is it. Just apply a multiplication factor and not an offset to preserve colors.
If you are not concerned with how bright the image has to be then, that is all there is.
If you are, then you need to know if your image data is linear, logarithmic or follows a gamma curve. That depends on the image format but most scientific data is stored linearly.