[PD] Reading a specific image from [pix_buffer] and saving it using [pix_write]

[Charles Goyard]

Seiichiro MATSUMURA wrote:
> Somehow colors are changed, the width become half and a picture itself
> is doubled.

iirc, in YUV you have a luminance layer (Y) and then the colors encoded
in a strange way, like 1 value for 2 pixels for the width in the U and V
layers. Well, something like that. Maybe it's a bug in the colorspace
conversion because you don't make it explicit ?