How to get summation of images

I have three images ( contrast feature,cluster prominence & cluster shade) with same size(0-255 range).I want to get the summation of this three feature images(sum_feature image).But,when get the summation, all pixel values in summation image are going to 255!(differences of pixel values are not appear).how to do this correctly?thanks!

Answer 1

[Image Analyst]

Because they are uint8, they get clipped at 255 anytime the sum would exceed 255. Cast them to double before adding them.