GDES45 Image File Formats

GDES 45 • Images

Comparing the file formats

jpg/jpeg

gif/giff

png

better for photographic type images(continuous tone)
millions of colors(16.7 million)
lossy compression(throws out information to reduce file size)
no transparency
no animation
has a newer version(jpeg 2000)
reduce file size by increasing compression(which reduces quality)

better for images with large areas of flat color like graphics, logos, etc.
lossless compression(although adobe now has lossy gifs)
256 colors or less
allows animation
allows 1 bit transparency(each pixel is either completely transparent or opaque)
reduce file size by reducing the number of colors

2 versions(8bit and 24 bit)
PNG preserves full transparency in grayscale and RGB images using alpha channels, but may result in larger files than jpg (using PNG-24)
Poorer browser support in older browsers like IE6(Transparency in PNG 24 files will not work)
PNG format supports RGB, indexed-color, grayscale, and Bitmap-mode images without alpha channels

These are the palettes you might use to optimize a gif.

Local (Perceptual)Creates a custom palette by giving priority to colors for which the human eye has greater sensitivity.

Local (Selective)Creates a color table similar to the Perceptual color table, but favoring broad areas of color and the preservation of web colors. This option usually produces images with the greatest color integrity.

Local (Adaptive)Creates a palette by sampling the colors from the spectrum appearing most commonly in the image. For example, an RGB image with only the colors green and blue produces a palette made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum. To control a palette more precisely, first select a part of the image containing the colors you want to emphasize. Photoshop weights the conversion toward these colors.

Comparing the file formats
jpg/jpeg	gif/giff	png
better for photographic type images(continuous tone) millions of colors(16.7 million) lossy compression(throws out information to reduce file size) no transparency no animation has a newer version(jpeg 2000) reduce file size by increasing compression(which reduces quality)	better for images with large areas of flat color like graphics, logos, etc. lossless compression(although adobe now has lossy gifs) 256 colors or less allows animation allows 1 bit transparency(each pixel is either completely transparent or opaque) reduce file size by reducing the number of colors	2 versions(8bit and 24 bit) PNG preserves full transparency in grayscale and RGB images using alpha channels, but may result in larger files than jpg (using PNG-24) Poorer browser support in older browsers like IE6(Transparency in PNG 24 files will not work) PNG format supports RGB, indexed-color, grayscale, and Bitmap-mode images without alpha channels