CHAPTER 12
216
Optimizing Images for the Web and E-mail
GIF without hard-edged transparency, and with hard-edged
transparency
To create hard-edged transparency in a GIF or
PNG-8 file:
1
Open or create an image that contains trans-
parency, and choose File > Save for Web.
2
In the Save For Web dialog box, select GIF or
PNG-8 as the optimization format.
3
Select Transparency.
4
Select None from the Matte pop-up menu.
Creating background matting in JPEG
images
Though the JPEG format does not support trans-
parency, you can specify a matte color to simulate
the appearance of transparency in the original
image. The matte color fills fully transparent pixels
and blends with partially transparent pixels. When
you place the JPEG on a Web page with a
background that matches the matte color, the
image appears to blend with the background.
To create a matted JPEG image:
1
Open or create an image that contains trans-
parency, and choose File > Save for Web.
2
In the Save For Web dialog box, select JPEG as
the optimization format.
3
Select a color from the Matte pop-up menu:
None, Eyedropper (to use the color in the
eyedropper sample box), White, Black, or Other
(to select a color using the color picker).
Note:
When you select None, white is used as the
matte color.
Previewing and controlling
dithering
Most Web images are created by designers using
using 24-bit color displays (which display over 16
million colors), but some users view Web pages on
computers with 8-bit color displays (which display
only 256 colors). As a result, Web images often
contain colors not available on some computers.
Computers use a technique called dithering to
simulate colors they can’t display. Dithering uses
adjacent pixels of different colors to give the
appearance of a third color. For example, a red
color and a yellow color may dither in a mosaic
pattern to produce the illusion of an orange color
that the 8-bit color palette doesn’t contain.
When optimizing images, keep in mind that two
kinds of dithering can occur:
•
Application dither occurs in GIF and PNG-8
images when Photoshop Elements attempts to
simulate colors that aren’t in the current color
table. You can control application dither by
choosing a dithering pattern, or you can try to
avoid application dither by adding more colors
to the table.
