Topic: Alpha channels

[Trop]

For N64 images alpha channels add trancparency when placed over a normal companion image.  And getting them to work in C4D is no problem for me, I just can't seem to get them to work in any 2D program.  I remember Peardian once telling me something about using them as masks in photoshop.  I figured out a trick with layers that kind of works but it's not really the same thing.  Any help?

[Peardian]

It's surprising how often this question arises. I blame the interface. Anyway, unlike the other times this question has popped up, this time I actually have a solution to link to!

This shows you exactly what you need to know.

[Trop]

Only that trick doesn't work for this problem.  How can I put this?
He goes: image + image + mask = new image
With the alpha you have to go: image + image mask = new image
In other words you have to somehow tell photoshop that the blacks, whites, and grays in the alpha image ARE the mask.  And that's what I can't figure out how to do.

[TerraEsperZ]

I remember having the same problem with Paint Shop Pro, and I eventually found out that there was an option to create a Mask Layer from an existing image. I unfortunately have no idea how to do the same in Photoshop.

[Trop]

Then I'm off to get Paint Shop Pro.

[Piranhaplant]

You can definitely do this with Photoshop
- Paste the original image into Photoshop as a new image
- Copy the alpha channel image
- Go to the image layer and click Layer->Layer Mask->Reveal All
- Go to the channels tab and make Layer name Mask visible
- Press Ctrl+V to paste into the layer mask

[Trop]

Gasp!  That's it!  Alright, alpha images are now on the menu.

[Trop]

And the first project/test is done:
http://www.vgmapper.com/SysPC/F/FateItemGallery_02.png

[Troy Lundin]

Figured I would post here since my question has to do with alpha channels. Does using pre-multiplied alpha cause any issues with general cartography? I know it renders a lot faster in my programs but I am wondering if it would cause any issues or inaccurate images.

[Trop]

Inaccurate transparency?  Hah.  I usually rebuild my transparencies in Photoshop with layers, how's that for inaccurate?  In other words as long as looks like the original, or is even just close enough, it's fine.  People look at maps with their eyes, they don't analyze the images with a program.
Example: https://www.vgmaps.com/Atlas/SuperNES/LegendOfZelda-ALinkToThePast-LightWorld-LostWoods%28Fog%29.png
I made this and it's totally wrong, but your eyes still get what they came for.