Technical data

78 Preparing Web Graphics
The .GIF format supports binary transparency. That is, any portion of
the image may be either fully opaque or fully transparent. Typically,
this is used to eliminate the box-shaped frame around the graphic that
would otherwise be present. Elements with rounded edges, such as
characters or shapes, preserve their contours over any background color
or pattern.
If you’re producing transparent GIFs, try to avoid anti-aliasing and
feathering (i.e. turn them off in the Tool Properties tab). The semi-
transparency these functions impart may look fine in PhotoPlus, but
remember that .GIF wants “all or nothing.” Pixels that aren’t 100%
transparent will end up opaque, and the exported graphic will display
sharp or even ragged edges when viewed over a Web page background.
GIF is also a multi-part format, which means one file can store multiple
images. As such, it’s the preferred format for Web animations.
Recommended .GIF export settings
Format (Bits per pixel): 8-bit (256 colors) is the only available setting
for animations, and the maximum supported by the format. For pictures,
4-bit (16-color) and 1-bit (2-color) exports are also possible.
Dithering (None, Ordered, Error diffusion): Dithering schemes
substitute pixel patterns for original colors to preserve apparent
coloration when the actual number of colors in the image is being
reduced. Choose Ordered (not available for animations) for a more
regular dot pattern, and Error diffusion for a more adaptive dot pattern.
Palette (Web-safe, Optimized): Choose Optimized to let the
PhotoPlus export filter determine the best colors to apply, but without
regard for standard colors. Choose Web-safe to reduce the colors to
only those found in the 216-color palette used by Web browsers. This
will ensure that an image you place on a Web page won’t change its
appearance when viewed by users of most other systems or browsers.
GIF Options (Transparent, Interlaced): .GIF files support
transparency—one reason they’re commonly used over backgrounds
on Web pages. PhotoPlus gives you the option of exporting GIFs with
or without a transparent background. Check Transparent to turn clear
“checkerboard” regions of your graphic (those with no pixels or 0%
opacity) into transparent regions in the GIF. All other regions will
become opaque. If unchecked, transparent regions will become white.
Check Interlaced to use an image format that will display
“progressively” in a browser: first a low-quality image will display,
followed by an improved image as the complete GIF is loaded.