Adobe ADBCD17648MC Manuel D’Utilisation
264
USING PHOTOSHOP ELEMENTS 8
Optimizing for the web
Optimizing for the web
Last updated 7/26/2011
About the 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.
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.
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, by which you blend the edges of the image with a web page
background color.
background transparency or background matting, by which you blend the edges of the image with a web page
background color.
More Help topics
About the 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.
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.
image to a wide audience.
The PNG-8 format uses more advanced compression schemes than GIF does, and a PNG-8 file can be 10% to 30%
smaller than a GIF file of the same image, depending on the image’s color patterns. Although PNG-8 compression is
lossless, optimizing an original 24-bit image as an 8-bit PNG file can subtract colors from the image.
smaller than a GIF file of the same image, depending on the image’s color patterns. Although PNG-8 compression is
lossless, optimizing an original 24-bit image as an 8-bit PNG file can subtract colors from the image.
Note: With certain images, especially those with simple patterns and few colors, GIF compression can create a smaller file
than PNG-8 compression. View optimized images in GIF and PNG-8 format to compare file size.
than PNG-8 compression. View optimized images in GIF and PNG-8 format to compare file size.
As with the GIF format, you can choose the number of colors in an image and control how colors dither in a browser.
The PNG-8 format supports background transparency and background matting, by which you blend the edges of the
image with a web page background color.
The PNG-8 format supports background transparency and background matting, by which you blend the edges of the
image with a web page background color.