nebula black background remove

[Verz Veraldi]

Hey,
I've saw a lot of nebula addon with their textures without the black sky background... Does anybody know how to do that?

[selden]

Celestia can use 24bit or 32bit PNG image files: each pixel has 8bits each of red, green, blue plus an optional 8 bits of opacity. JPEG images have only the three color channels.

What one does is create a "mask" from the original picture (probably jpeg), with black where it should be transparent and white where it should be opaque. One then converts the original image into a 4 channel PNG image which includes that mask. The resulting picture or the model that it's applied to will be partially transparent when drawn by Celestia.

Describing exactly how one creates such a mask would take more time than I have right now. There are a variety of methods, some automated and some manual, some scripted and some using paint programs.

[Verz Veraldi]

oh, then if you're busy perhaps you can show me some tutorials created by others? I do understand what you mean by the 4 color channel. red green blue and alpha right? maybe i'll do something with photoshop.. thanks anyway..

[selden]

If you use google to do a Web search with the keywords
create alpha channel mask
the first few results are tutorials for Photoshop.