David Mullen ASC
Moderator
I see, so it's the wavelet (hope I'm getting the term right) compression holding internal down-scaling back?
I believe that to downscale raw well, you'd have to debayer it to an RGB codec, otherwise you're stuck doing things like line skipping and pixel binning to reduce the number of pixels being recorded in raw without doing the debayering first. Remember a raw image is monochromatic with this complex Bayer filter pattern that filters specific photosites for red, green, or blue information, so downscaling without first debayering that to RGB is difficult, and pixel binning and line skipping to reduce the pixel count can lead to chroma aliasing problems.
So basically either you record full sensor raw or some cropped portion, or you debayer and downscale it if you want and record that in some RGB codec.