You realize that Bayer data counts every column and row whether R G or B, right? Half the pixels (21Mpix) are green and the other 2 quarters are R and G. So if

You realize that Bayer data counts every column and row whether R G or B, right? Half the pixels (21Mpix) are green and the other 2 quarters are R and G. So if you're going down to FHD (2kx1k) from 42Mpix (8kx5k) you have already lost massive ammounts of resolution (and noise). Bayer FHD would be SPR (sup-pixel rendered) and even lower resolution (1/3 RGB e.g. 1080 lines of 1920 RG/BG alternating columns) than most JPEG FHD (natural scene) not suitable for video compression much less Raw. That would be silly. If you don't down-sample the data somehow you can't even get it off the CIS which are limited to ~2-5Gb/sec. Since most reasonable image sizes are large enough you can see color at full resolution we typically use RGB at FHD, compressed or not. Alternately, you can go to 4:4:4 to 4:2:2 or even 4:1:1 in Yuv (YCbCr), but that's not Raw or anything like it.