Saving Image in a File Format After you modify a digital photo, whether it’s to adjust the display size or to perform-retouching or creative work, you need to save the file in a format that is compatible with programs used to display screen pictures—web browsers, e-mail programs, presentation programs such as Microsoft PowerPoint, and the like.
PNG is also a lossless storage format.
GIF creates a table of up to 256 colors from a pool of 16 million.
GIF achieves compression in two ways. First, it reduces the number of colors of color-rich images, thereby reducing the number of bits needed per pixel, as just described. Second, it replaces commonly occurring patterns (especially large areas of uniform color) with a short abbreviation: instead of storing “white, white, white, white, white,” it stores “5 white.”Thus, GIF is “lossless” only for images with 256 colors or less. For a rich, true color image, GIF may “lose” 99.998% of the colors.
JPG is optimized for photographs and similar continuous tone images that contain many, many colors. It can achieve astounding compression ratios even while maintaining very high image quality.
RAW is an image output option available on some digital cameras.
TIFF is, in principle, a very flexible format that can be lossless or lossy.
BMP is an uncompressed proprietary format invented by Microsoft. There is really no reason to ever use this format.
PSD, PSP, etc. are proprietary formats used by graphics programs. Photoshop’s files have the PSD extension, while Paint Shop Pro files use PSP. These are the preferred working formats as you edit images in the software, because only the proprietary formats retain all the editing power of the programs.