Graphic Elements

	Standard Web graphic formats GIF - Graphics Interchange Format JPEG - Joint Photographic Experts Group PNG - Portable Network Graphics ("ping") A replacement to proprietary GIF Can be stored at various bit depths Uses lossless compression Supports gamma correction, alpha-channel transparency & 8-bit transparency PNG is too new at this time (Spr'98) PNG Web sites: http://www.w3.org/TR/REC-png-multi.html http://www.cdrom.com/pub/png Image compression Makes image smaller (storage/downloading) Client computer decompresses the images Lossless compression No image data is discarded during compression GIF uses LZW (Lempel-Ziv & Welch) compression (similar to RLE) Lossy compression Image data may be discarded during compression Different levels of compression available Low compression - high quality images Medium - usually good quality images High - image artifacts, poor quality (may) begin to show Run Length Encoding (RLE) compression Compresses images horizontally That is, RLE is bad for horizontal gradients Use top-to-bottom gradients instead Image size and file size Keep image file sizes as small as possible Keep total page size under 40 kilobytes (100KB at most) Avoid huge graphic files Break them down into smaller images Netscape can load multiple files at the time! Use individual graphics/links instead of huge imagemaps Use preview/thumbnails for large images Let users know about size of large images, or other multimedia content; e.g. (80KB) Exploit the browser's cache: reuse images already downloaded Avoid anti-aliasing, too many colors and too much dithering Image (IMG tag) attributes Use HEIGHT= and WIDTH= attributes for fast layout Use Alt= attribute for alternate text Helps character-based browser users Users who have disabled auto image loading see alternate text New browsers display it on "mouseover" Use Lowsrc= attribute for low quality previews An example of a lowsrc image: http://ccwf.cc.utexas.edu/~kiele/   The Browser-Safe Color Palette What is it and why use it? When not to use Web-safe colors Lynda Weinman's Browser safe color page An example Unix vs Windows/Mac color palettes Unix versions of Netscape use a different color palette than Win/Mac versions. For SunOS and 24/8-bit monitors, use hex values with 00, 40, 80, BF or FF pair combinations.   ITL Graphic Resource Links   McCannas.com Free Art Site   Barry's Clipart Server
	Sometimes bad image management can detract from a Web page: http://saweb.uta.edu/sports/recreation.htm