Memory usage for BW images

Support Materials and Textures
1

I’ve been working on a project with some large image maps, and noticing that I often end up with two or three black and white factor maps saved as PNGs. Given it’s a big project and memory might start to be a limiting factor in the future, I used photoshop to paste each BW image into a separate channel, and then used a “separate RGB” node to extract the maps.

From an organisational level I’m pretty happy with that, but I was wondering whether I’m kidding myself about the memory savings, so I thought I’d ask if anyone more technical than me knew - if Blender loads a BW image as BW data rather than RGB data (I presume it’d have to be a PNG saved as BW only, since that’s the only way Blender would know ahead of time that RGB wasn’t needed). Presumably three single channel 4k textures are going to take the same memory constraints as one triple-channel 4k textures. Anyone know if Blender does that?

The sensible thing to do would be to run a benchmark render comparison, which I’ll probably do eventually.

2

Here is a quick non-compressed png size comparison. What’s in file is described in image header data inside the file so that Blender has no problems acting appropriately.
PS might have it’s own idea what png type it produces; you can check this by loading image in Blender’s UV editor.

3

It depends how exactly does cycles load textures into GPU memory. Devs can answer that but you can also test it using a very large resolution image. First as a BW and then as RGB, large enough to fill up considerable amoubt of mem on GPU. If memory usage does not differ, you will not gain anything using BW images.