When I use a image as a texture, there is an option for using an Alpha Channel. Can anybody tell me what this is about?
Some file formats are capable of taking an alpha channel (for example tif, targa and png) along (some take even more than one). An alpha channel is basicly an 8 bit grayscale picture. If you click “use alpha” in the texture buttons, this channel controls the opacity of your picture.
It is unwise to use alpha channels in blender. If you are only using color that’s fine, but if you are trying to use the same texture for spec/ref/nor you will find disastrous results. I do not know why blender did not allow the other material properties to recognize the alpha channels as well.
DAK: I don’t clearly see what you mean. I’ve been using alpha channel for texturing purpose in Blender for ages, and there’s no problem if it’s done the right way. Of course, it is always unsafe to use the same texture for alpha and color at the same time, since the alpha channel might not operate the way you think it does.
DAK, could it be that you are using your normal image as an alpha mask?
If you do, Blender will take the average brightness value as an alpha mask. This cannot produce predictable results. So either take a second texture (grayscale) as an alpha mask or use the above mentioned version. I think Gimp should be capable of saving a separate channel. Photoshop definitely is. I just tried it when you posted.
“use alpha” has also the advantage, that only your picture is trannsparent. So you are able of mixing material color with images.
Thank you for your answers. I will try to see if I can get it working.
There needs to be a UseAlpha for bump mapping. Without this you end up bumping everything. This is a big problem.
Huh? Just add another texture for bumpmapping. Bump maps are essentially transparent as long as you are only using the NOR setting. Maybe nobody understands where you are coming from on this subject. Can you give us an example?