Transparency, File Formats, & 2d Editors

I was playing around with using multiple copies of the same image mapped onto different planes with different parts erased (alpha) to give a 3D effect.

I’m using Blender 2.58.1, PhotoShop Elements 8, and Corel PaintShop Photo Pro X3. I started with a jpg which I resized to 2048x2048. Then I cut out sections and erased(Alpha) around elements I wanted with Corel and saved them as 1024x1024 pngs and maped them to planes in front of the background.

First, the 3d window doesn’t show the alpha channel as transparent in texture mode: no big deal. The UV window showed black edges that appeared transparent in Corel; I mapped them out. When I render I get horible black and white artifacts along the edges of the alpha mask where there is partial transparency and there were other places that appeared to have the same problem. No amount of repainting/reloading could get rid of these.

At this point I thought maybe Blender had some sort of image buffer that wasn’t getting flushed. Restarting didn’t help. Then I painted some color over the alpha and reloaded. It showed up! Then I tried erasing the color. It disappeared in Corel but reloading into Blender didn’t get rid of the color!

So I figured I’d try PhotoShop. Loaded into Elements and everything looked great but I ran the eraser over the problem area anyway. Saved it and reloaded into Blender. Now most (but not all) of my alpha is white! No amount of re-editing in either program fixed the alpha though it looks fine in both editors.

Is my problem Corel, Elements, Blender, the PNG format, or am I an idiot.

First, the 3d window doesn’t show the alpha channel as transparent in texture mode

Set the display shading to GLSL

When I render I get horible black and white artifacts along the edges of the alpha mask where there is partial transparency

In the Texture / Image settings select ‘Premultiply’ or in the Render / Shading panel set the Alpha to ‘Premultiplied’

Thanks for helping.

Premultiply on texture/image makes my alpha look black in both 3d and render (but it got rid of the color I painted in). Premultiply on render doesn’t appear to do anything.

Where do I find the GLSL setting?