Adobe 29180155 - Photoshop Elements 4.0 User Manual page 265

ADOBE PHOTOSHOP ELEMENTS 4.0 260
User Guide
The JPEG format does not support transparency. When you save an image as a JPEG file, transparent pixels are filled
with the matte color specified in the Save For Web dialog box. To simulate the effect of background transparency,
you can match the matte color to the web page background color. If your image contains transparency and you do
not know the web page background color, or if the background is a pattern, you should use a format that supports
transparency (GIF, PNG-8, or PNG-24).
See also
"To create a matted GIF or PNG image" on page 267
"To optimize as JPEG" on page 262
About GIF format
The GIF format uses 8-bit color and efficiently compresses solid areas of color while preserving sharp details like
those in line art, logos, or type. You also use the GIF format to create an animated image and preserve transparency
in an image. GIF is supported by most browsers.
The GIF format uses LZW compression, which is a lossless compression method. However, because GIF files are
limited to 256 colors, optimizing an original 24-bit image as an 8-bit GIF can subtract colors from an image.
GIF image with Selective color (left), and GIF image with web color (right)
You can choose the number of colors in a GIF image and control how colors dither in a browser. GIF supports
background transparency or background matting, in which you blend the edges of the image with a web page
background color.
See also
"To optimize as GIF or PNG-8 format" on page 263
"To preserve background transparency in a GIF or PNG image" on page 267
About PNG-8 format
The PNG-8 format uses 8-bit color. Like the GIF format, PNG-8 efficiently compresses areas of solid color while
preserving sharp detail like those in line art, logos, or type.
Because PNG-8 is not supported by all browsers, you may want to avoid this format when you are distributing the
image to a wide audience.