|Some ins and outs of transparent GIFs and PNGs.|
Before I begin, I suggest you review these
FAQs. They will give you an understanding of image file formats that
will be greatly helpful, regardless of how well you understand them.|
Here we go. So I'm making a pic. I will make an image I want to post as a transparent gif. In PSP, the transparent area is a checkerboard. You can change the colors of it to anything you want. The doodle is ready. Mitsuko 1/1. Hah hah. She seems nonplussed. The edges of the text is hard, fully aliased. There isn't the least bit of smoothness to them.
Now I will flatten the layers. (I have my background palette color set to white for this example, and so the transparent areas of the image will become white.)
That's done. The image is now a single layer, the background layer. Now I will paint in the area I want to be transparent. I use bright green as my transparency color, because I almost never use it in my work. When the colors are reduced to 256, the green will not appear anywhere outside of where I painted it, because it's not even close to the other colors in the image. It will not be used to replace any other colors.
Setting the color green as the transparent color... Now I will post it on the web. Hey, wtf?! There's crud all around poor Mitsuko-tan! Why?!
Dig it. Transparent GIFs use 1-bit transparency. This means the pixel
is either solid or transparent, nothing in between. The white
background that was replaced with the green was fully white, not even
light gray with a tolerance in either direction. Only the white was
replaced. The white that blended in with the black became gray. The
text is fine because it was drawn with a hard-edged brush. No smoothing
whatsoever. Fully opaque, so none of the transparent background showed
through. The only way to avoid this halo of junk is to trim the border
of the area that will be affected, or to make sure everything bordering
the transparent area has a hard edge. Sometimes this can look like
crap. In the days ofl the ancient internet, this rarely mattered,
because most web pages were gray or white. Now we have thousands upon
thousands of colors, and background images. One has to carefully
construct their transparent images...