Image Formats
GIF (Graphics Interchange Format)
  • Compressed graphics format developed in 1987 by CompuServe.
  • Lossless
  • Compresses 8-bit color (256 color) images
  • By definition, can't handle over 256 colors
  • Usually best for compressing low-color cartoon-like images, line drawings, and logos.
  • Allows transparency. You can choose one color in the color palette that maps transparently when displayed. Gives the effect of seeing through an image or of an image floating on a background.
  • Allows interlacing or interleaving. Allows browsers to display a low-resolution image that appears immediately and continually redraws until it reaches its highest resolution.

JPEG (Joint Photographic Experts Group)

  • Lossy
  • Most efficient
  • Stores 24-bit color (16,777,216 color) images
  • Designed for compressing either full-color or gray-scale images of natural, real-world scenes. Works well on photographs, naturalistic artwork, and similar material. It does not work well on lettering, simple cartoons, or line drawings.
  • Does not allow transparency.
  • Does not allow interlacing or interleaving.

Converting GIFs to JPEG

This should be done with great care because the results can compromise your image quality quite a bit. Because both GIF and JPEG formats have their limitiations, you can run into trouble mixing the two. Following are some hints if you have to convert.

  • Never convert an image that's not appropriate for the JPEG format as described above.
  • Look at the JPEG image after you've converted it to make sure it is acceptable before you throw the older GIF image away. it's also possible that the JPEG image is larger than the GIF image.
  • Get rid of any borders on the image. This not only wastes space in a JPEG format, but can degrade the quality of the image. The border is compressed extremely well in the GIF format.
  • Know where the image came from. Repeated GIF to JPEG conversions can wreak havoc on your images because the quality is degraded somewhat each time the conversion takes place.
  • Gray-scale images usually do well, however color images pose more of a problem. Because colored GIFs of photographic-type images are usually dithered, it creates more of a problem for JPEG conversion resulting occasionally in larger files than the original GIF image.

Other popular formats (not widely supported on the WWW):

  • Photoshop - Versions 2.0, 3.0, and now 4.0. The "de facto standard" for image editing on the web. Perfect format to save originals before converting to other formats such as GIF and JPEG.
  • TIFF - Tagged Interchange File Format. The standard format used in the printing industry. File sizes tend to be extremely large in comparison with GIF and JPEG.
  • PICT - PICTure format. The Macintosh Standard Image Format.
  • BMP - BitMaP format. The Windows Standard Image Format.
  • Targa - TrueVision format. Supports 32-bit images.
  • PCX - PC paintbrush format.
  • EPS - Encapsulated PostScript format. Used heavily for printing to postscript output devices.
  • RIFF - Raster Image File Format. Fractal Design Painter's proprietary format.