Color balance Write a simple application to change the color balance of an image by multiplying each color value by a different user-specified constant. If you want to get fancy, you can make this application interactive, with sliders.
1. Do you get different results if you take out the gamma transformation before or after doing the multiplication? Why or why not?
2. Take the same picture with your digital camera using different color balance settings (most cameras control the color balance from one of the menus). Can you recover what the color balance ratios are between the different settings? You may need to put your camera on a tripod and align the images manually or automatically to make this work. Alternatively, use a color checker chart (Figure 10.3b), as discussed in Sections 2.3 and 10.1.1.
3. If you have access to the RAW image for the camera, perform the demosaicing yourself (Section 10.3.1) or down sample the image resolution to get a “true” RGB image. Does your camera perform a simple linear mapping between RAW values and the color balanced values in a JPEG? Some high-end cameras have a RAW+JPEG mode, which makes this comparison much easier.
4. Can you think of any reason why you might want to perform a color twist (Section 3.1.2) on the images? See also for some related ideas.