Creating images for the World Wide Web (WWW)

Personal Paint is an ideal tool for the creation of palette-based images
to be included in HTML documents (a standard for WWW pages). Two file
formats are recommended for this purpose: GIF and PNG. Both formats
support progressive display and transparency, the appropriate use of which
can make a difference between a good page and a poor page. We recommend
the use of both features.

PNG is technically better than GIF, but it has been officially introduced
to the list of WWW-supported formats only in 1996. It is likely that PNG
will slowly replace GIF, which is being suffocated by patent problems. At
Cloanto we began using GIF for our WWW images, but we expect to replace it
with PNG as more and more browsers support it.

Progressive display is a feature which is useful whenever it takes a long
time (seconds, if not minutes) to load an image. Images stored without
this option can be displayed only line by line, from the top to the
bottom. It is very difficult to have an idea of the contents of such an
image at the beginning of the transmission. If instead the progressive
display option was enabled when the original image was saved, the entire
image can be viewed in a coarse resolution at the beginning of the
transmission, and during the transmission it becomes progressively more
detailed.

All versions of GIF and PNG support progressive display, although PNG uses
a more appealing method. Personal Paint has a Progressive Display setting
in the Options window of the Save Image and Save Brush requesters. Images
saved using this option occupy slightly more space, but can be displayed
progressively during the load. This feature is widely used on the
Internet, and it is compatible with all WWW browsers.

Transparency is a feature which allows part of the image to be defined as
transparent. This is useful, for example, when non-rectangular images have
to be displayed over a pattern. But even if the background of a
non-rectangular shape has the same color of the page background, we
recommend setting that color as transparent, because some browsers may
remap the image background to a slightly different color than the page
background color. Some WWW browsers do not support the HTML commands which
set the page background color, so an image background which was intended
to be the same as the page, could appear to be different. Transparency can
prevent this. Active use of transparency helps maintaining the quality of
the page even when these browsers are used.

To preserve the best possible page quality even with older browsers we
recommend to use transparency and at the same time to also make sure that
the transparent color is the same as the page background color. This helps
with those few browsers that do not support transparency.

Personal Paint saves transparency information only when saving brushes
(Save Brush command, rather than Save Image). The transparent color is
defined when the brush is defined. If the Transparency option in the
Settings menu is set to None, then no transparency is associated to the
brush. If instead it is set to Color, then the background color during the
brush definition is used as transparent. Other types of transparency, such
as transparency shapes which are not associated to a single color, which
can be defined and stored in the IFF-ILBM format, are poorly supported on
the Internet, and not at all supported by the GIF format. So the only way
to mark a region as transparent is to reserve a color for that part of the
picture, and selecting it as the background color before the brush is
defined.

GIF exists in two variants: GIF87a and GIF89a. PNG and GIF89a support
transparency. GIF87a does not. The GIF format is designed in a way that
programs supporting only the "87a" format should be able to read "89a"
images, skipping the transparency information. Personal Paint's GIF
input/output libraries ("personal_gif_io.library" from version 3.2) allow
for the GIF version to be specified in the Options window of the Save
Brush requester.


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