Ha, I was going to describe it the same way. The image is there in the buffer, you have full bit-level access to it; the only difference is that there's a firewall preventing it from being rendered to the primary display. Dreaming allows rendering it to a virtual display which is temporarily considered canonical.

I think the resolution and bit depth of that buffer is the aphantasia spectrum. Some people are working from a 160x120 1-bit image, for some it's 640x480 8-bit, and some can load up an 8K at 32-bit deep color.