How to modify the pixel value and save in same format

Hi how to modify pixel value image having alpha channel and save it as same format

[Image Analyst]

Why are you asking this when you already have a conversation going on here: http://www.mathworks.com/matlabcentral/answers/57664-how-to-add-alpha-channel-to-the-image-and-convert-that-image-into-png-format?