imaging exercise

[AeonFlux1212]

Hi! I want to write a program to resize images, and I'm wondering if any of you guys know where I could find reliable information about image file formats (jpeg, png, bmp, etc.), like how the files are read (bitwise) and what are the algorithms they use for compression, if any. Also, what is the physical shape of an individual pixel on a laptop LCD screen, is it square? Or 16:9, or another shape? Thanks a lot!

AeonFlux1212