Pixels into Binary
Binary in a image
Information on Bits in photos
A common sample format is 8bit integers, 8bit integers can only represent 256 discrete values (2^8 = 256), thus brightness levels are quantized into these levels.
For high dynamic range images (images with detail both in shadows and highlights) 8bits 256 discrete values does not provide enough precision to store an accurate image. Some digital cameras operate with more than 8bit samples internally, higher end cameras (mostly SLRs) also provide RAW images that often are 12bit (2^12bit = 4096).
The PNG and TIF image formats supports 16bit samples, many image processing and manipulation programs perform their operations in 16bit when working on 8bit images to avoid quality loss in processing.