I need to calculate the color histogram of images in order to get a feature for finding similarity between images. (description: https://stackoverflow.com/a/844113/5142270 and https://en.wikipedia.org/wiki/Color_histogram).
The only problem I am facing is in deciding how to scale the images so that they will have the same number of pixels. Is there a standard image size(in pixels) that is used by researchers for this purpose, when there are thousands of images that can be of any dimension? I tried searching a lot on how to scale the images, but was unable to find out what was supposed to be done.
Thanks in advance.