Image Formats

What makes one image format different from another? Differences What makes one image format different from another?

Compression Images can be large files More disk use Slower downloads Compression – ways to cut size of file Can be Lossy or Lossless

Lossy vs. Lossless Lossless Lossy No information is lost Find other ways to make file smaller Ex: look for recurring pattern in picture and replace each occurrence with a short abbreviation Lossy Accept some degradation of image Example loss: Store color info at lower resolution since eye not so sensitive to changes in color

Number of Colors More colors = more memory required to represent each pixel Different file types accommodate different numbers of colors

(Tell them apart based on the file extension – the part after the dot) File Types (Tell them apart based on the file extension – the part after the dot)

Tagged Image File Format TIFF Usually no compression Very large files Cannot put directly on website May come from high quality camera Tagged Image File Format

RAW Lossless 3-4x smaller than TIFF Different according to manufacturers of device generating image Cannot put directly on website

Bitmap BMP Uncompressed Proprietary format invented by Microsoft Cannot put directly on website Possibly coming from Microsoft Paint Bitmap

Photoshop Document Paint Shop Pro PSD, PSP Cannot put directly on website Photoshop Document Paint Shop Pro

Portable Network Graphic PNG Lossless image format Looks for patterns to compress file size Compression is exactly reversible (no loss) Allows transparency and partial transparency CAN put on website Portable Network Graphic

Graphics Interchange Format GIF Lossy Creates table of 256 colors If image has fewer, can render exactly If more, GIF limits down to 256 colors If image is true color, GIF may lose 99.998% of colors Allows transparency Allows animation CAN put on website Graphics Interchange Format

Joint Photographic Experts Group JPG / JPEG Lossy Optimized for photos Very good compression while maintaining high image quality Degree of compression is adjustable Use on web for photos Do not use for line art or images with large areas of a single color with sharp edges CAN put on website Joint Photographic Experts Group