Adobe 65045315 - Photoshop Elements Use Manual page 295

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USING PHOTOSHOP ELEMENTS 10
Optimizing for the web
Like JPEG, this is a good format for photographs. Choose PNG-24 rather than JPEG only when your image
PNG-24
contains transparency. (JPEG does not support transparency; you must fill it with a matte color.) PNG-24 files are
often much larger than JPEG files of the same image.
GIF is the format to use for line art, illustrations with large areas of solid color and crisp detail, and text. Also, if
GIF
you want to export an animated image, you must use GIF.
PNG-8 is a lesser-known alternative to GIF. Use it for the same purposes (except animation).
PNG-8
Images in GIF and PNG-8 formats, sometimes called indexed-color images, can display up to 256 colors. To convert
an image to indexed-color format, Photoshop Elements builds a color lookup table. If a color in the original image does
not appear in the color lookup table, the application either chooses the closest color in the table or simulates the color
using a combination of available colors.
JPEG and PNG-24 files support 24-bit color, so they can display up to 16 million colors. Depending on the format, you
can specify image quality, background transparency or matting, color display, and the method a browser should use
to display the image while downloading.
The appearance of an image on the web also depends on the colors displayed by the computer platform, operating
system, monitor, and browser. You may want to preview images in different browsers and on different platforms to
see how they will appear on the web.
About the JPEG format
The JPEG format supports 24-bit color, so it preserves the subtle variations in brightness and hue found in
photographs. A progressive JPEG file displays a low-resolution version of the image in the web browser while the full
image is downloading.
JPEG image compression is called lossy because it selectively discards image data. A higher quality setting results in
less data being discarded, but the JPEG compression method may still degrade sharp detail in an image, particularly
in images containing type or vector art.
Note: Artifacts, such as wavelike patterns or blocky areas of banding, are created each time you save an image in JPEG
format. Therefore, you should always save JPEG files from the original image, not from a previously saved JPEG.
Original image (left), and optimized JPEG with Low quality setting (right)
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).
More Help topics
"Create a matted GIF or PNG image" on page 296
Last updated 1/2/2012