How to find color space from screen grab video/pictures (yuv444p ffv1, rgb png)

[zn]

How to find color range from screen recordings saved as FFV1 video (yuv444p) or PNG pictures (rgb) or RAW BGR24 video (rgb)?
I need approximates values to find information about source/decoder settings (both hidden using proprietary technologies):

a) 0-255 (not compressed by source, not compressed by decoder/videocard)
b) 16-235 (compressed by source OR compressed by decoder/videocard)
c) 30-218 (compressed by source AND compressed by decoder/videocard)

ffmpeg -r 25 -f x11grab -video_size 960x540 -i :0.0 -t 00:01:00 rgb-%03d.png
ffmpeg -r 25 -f x11grab -video_size 960x540 -i :0.0 -t 00:01:00 -vcodec ffv1 ffv1.mkv
ffmpeg -r 25 -f x11grab -video_size 960x540 -i :0.0 -t 00:01:00 -vcodec rawvideo -pix_fmt bgr24 raw-bgr.avi

[Emulgator]

I would apply histogram(mode="classic").histogram(mode="levels") and watch the populated range.