Blender Git Loki

Optimization for render result save

Skip byte->float conversion if output file format
supports high bit depths but configured to only
output 8 bits per channel.

Gives around 30% speedup when re-exporting movie file
to PNG image sequence here on laptop.

Possible further optimization:

- Skip color space conversion in imbuf_for_write
function if we've got already have buffer in
that space.

This doesn't seem to happen often after tweak
to render result to imbuf.

- Skip black alpha-under if original image is
opaque,

This is a bit tricky to detect.