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

Christoph Gerstbauer christophgerstbauer at gmail.com
Tue Mar 10 11:10:28 CET 2015

Am 09.03.2015 um 20:50 schrieb 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).

yes that is what I am planing to do.

> 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

Where can I find this GM tool? Is this tool for linux and for windows?

> Carl Eugen
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