how i can convert two different images to identical form?

I work on registration between two images the first is X-RAY and the second is normal , to do this function i need initially to convert these two images to identical format in order to find correspondences between them . if can help me in code please

Answer 1

[Image Analyst]

See this link: http://www.mathworks.com/matlabcentral/answers/88422#answer_97969