is there such a thing as single channel texture in vram?

[MichaelJPCT]

i think all textures have 3 or 4 color channels. but sometimes a texture has no color , only greyscale info is needed.
if the texture in vram is stored as single channel, then it occupies 1/4 of memory. isn't it great?

another question, can RTT texture be ETC compressed in vram?

[EgonOlsen]

Yes, in theory you could do that but it's not supported in jPCT-AE and, at least some years ago, it wasn't well supported on devices either.

A RTT texture can't be compressed, I'm afraid.