[FFmpeg-user] Questions about readout important metadata from DPX files ("logarthmic/linear") and recreate DPX with same metadata

[Carl Eugen Hoyos]

Christoph Gerstbauer <christophgerstbauer <at> gmail.com> writes:

> > (This is not the first time that I am slightly
> > surprised people use FFmpeg to prove that an
> > encoder of FFmpeg is lossless.)
> Do you have any ideas for proving the 
> losslessness with other tools than ffmpeg?

You could use gm to convert both the original 
and the converted file to a raw format and 
compare.

But let me try it differently:
You have an input file with a logarithmic 
colour space that is not supported by FFmpeg.
If you are sure that you know what you are 
doing, you can of course use FFmpeg to 
compress your raw data (I believe ffv1 was 
tested much better already but this is not 
really related). But while the data will 
still be identical the colourspace will 
be linear because FFmpeg only supports 
linear colourspaces. So you will will have 
to "know" that the actual content is 
logarithmic when you use it again (or 
write the transfer information when 
creating the file).

It appears to me that gm ignores the 
transfer information just like FFmpeg, I 
tested with:
$ gm convert -define tiff:bits-per-sample=16 LOG_ORIGINAL.dpx out.tif

Carl Eugen