Transparent gif's
Graphic programs give us the ability to designate only one solid color as transparent when saving a transparent gif. The designated color will be ignored on the web page and will not be displayed. See the two figures below.
Aliased gif without transparency.
Same aliased graphic saved as a transparent gif choosing white as the transparent color. This
web page is ignoring the white background and not displaying it. Doesn't look too bad, however
we still have the jagged aliased edges. So the obvious answer is to use an antialiased graphic to
save as a transparent gif. Doing this does present a new problem though. Note the figure below.
This is an antialiased transparent gif with white chosen as the transparent color. It appears
to have a jagged white halo around it. Remember those added gray shaded pixels used to
smooth out the edges? They may look white but they are actually light gray and since I choose
white as the one color to make transparent, the gray pixels are left behind. Since they contrast
with the blue web page background they show up as the jagged halo you see here. The obvious
fix then is to chose a similar, or the same color, you are using for the web page background as the transparent color for the gif.
Same antialiased graphic except blue chosen as the transparent color. The added shaded pixels are still there but they are now varying shades of black to blue instead of black to white. They do not contrast with the blue web page background and are not apparent.
Displaying transparent gifs on a single color web page background is relatively easy then. Simply
choose the same color as your web page background as the transparent color of the gif. Actually if your graphic background is exactly the same color as the web page background there's no reason to make it transparent. It will blend in anyway. However displaying transparent gifs on a textured or graphic background presents a few new problems.CONTINUE ON NEXT PAGE FOR DISPLAYING TRANSPARENT GIFS
ON TEXTURED OR IMAGE BACKGROUNDS.
