I’m learning how to optimize my textures and materials and i’ve been wondering. Why would photoshop allow you to have multiple alpha channels? what’s the purpose in such a thing? Can UE4 even utilize multiple alpha channels from a single texture file? If so how does this work as when i look at a texture node in my materials i only can ever see one drag off point for an alpha channel from any given texture i import. How do i select which alpha channel i wish to use if it only shows one even when there are multiple alpha channels in the texture file? I’ve been trying to figure this out for a few hours now honestly and the documentation epic games created for UE4 isn’t helpful in the least especially when it comes to more advanced areas of material creation like this.
This has nothing to do with Unreal. Typical image formats such as .png, .jpg, .tga, etc, only support three or four channels; red, green, blue, and some also alpha. Photoshop can use more channels to use as masks, but is AFAIK only supported in Photoshop’s own .psd format. You can import .psd in Unreal, but the engine converts it to a normal four channel format.
Than it absolutely has everything to do with Unreal. You said it yourself Photoshop format can use multiple alpha channels for masking, and you can import PSD formats into Unreal but UE4 automatically converts the PSD into a standard 4 channel format. Does this not directly contradict your statement that it has nothing to do with unreal?
also that basically means you can never actually use multiple alpha channels from a single texture file in unreal then. **** that sucks 
A .psd file is not a normal image format. It’s a lossless proprietary project format from Adobe. AFAIK, no other program can use it other than Adobe software. Other programs can read it to view the file (such as xnView), or convert it into a normal image, which is limited to three or four channels. .psd files contain all the information necessary for Photoshop, such as layers, adjustments, and more. Other programs have no use for it, as we have standardized formats that everything else uses.
If you want to efficiently use multiple alpha channels, combine four grayscale textures into a single image (one texture per channel), then access each channel separately in the material. There is no other way to do this.
As far as I know, Photoshop does not allow multiple alpha channels if you check under the channels tab. Only one.
Photoshop does support multiple channels, but there not really alpha channels like used by images. They’re only used internally as masks for shape layers. You can create as many as you want I believe, but only Photoshop can use them.
Last i checked, PS only has ONE alpha channel.
What you are talking about are MASKS, They are used to control what parts of a layer are blended into the final image.
You could do the same in UE, You would just need to use a lot of textures and samplers to achieve it.
HTH