Welcome back. I had a follow-up question on transparency which asked a question about this:
Particularly, the question came up that the reader couldn't get the check box to remove unused colors to be active so he could check it and save his image as transparent. In case you don't understand, here's what I mean:
That part that's lit up in that picture. The truth is that you don't need it checked -- if you put your image on a transparent work space, change the mode to "indexed", when you save it as a ".gif" file it should leave the transparent parts transparent whether you remove the unused colors or not.
But the truth is this: if you remove unused colors, the file will save to a smaller size, and while in this world of DSL, 3G and high-speed cable you prolly don't care about file size, you can be a good neighbor and reduce your file sizes for the sake of merely improving the net load time of your images.
To get that box checked, do this:
You can check any of the color-indexing options, and the check box will magically become an active check box. And you can leave it checked in case you think you're missing something when you tell GiMP to reduce the colors for you.
One last note: without getting mired into Geek Speak, when you reduce colors you will have the best results when you reduce to these numbers of colors:
These are the natural breaks in color resolution which your computer still understands even though for the most part you all have something like 65,000+ color HD-resolution monitors. This is what will get you the best file size reductions because of the way .gif format helps your computer and your software think about color.