Subject: [Cellar] Fwd: FFV1 and DPX

From: Kieran O Leary <[email-masked]>
Date: Fri, 15 Jul 2016 20:40:44 +0100

Hi,

I'm posting this on CELLAR so that the information isn't just on a
private thread.  Essentially my findings were that LOG DPX to FFV1 was
a lossless process in terms of the image data, as verified by the
framemd5 comparisons, which was already known.

I did some testing with DaVinci Resolve and Avid Media Composer 8 (see
the forwarded email below this one)with the source LOG DPX and the DPX
files that were transcoded from FFV1.

While the color primaries were always listed as 'Linear' in
mediainfo/exiftool when transcoding from FFV1 to DPX, regardless of
the source DPX color primaries, DaVinci Resolve treated the files in
the exact same way and produced identical values on the scopes. This
was because Resolve does not attempt to guess which LUT is required
and lets the user choose their own setting.

The email below this one shows my findings with Media Composer 8, with
screenshots attached. It appears that MC8 is reading the metadata
values for color primaries, and is guessing which LUT is correct based
on what it finds. As such, the source DPX will appear different to the
FFV1/DPX transcode, but this can be rectified by removing the LUT
defaults.

It is ideal if FFV1 (and the resulting DPX transcode) can contain the
correct color primary values for not only being consistent with the
self-descriptive nature of FFV1, but also so that post production
tools have a better chance of choosing the correct preset. It's also
significantly better for long term preservation if these values are
more accurate.

However, while I am reluctant to adopt FFV1 for LOG DPX until the
metadata issue is fixed somehow, I am not ruling it out entirely as
we, as an archive, would have to find a way to make it clear to future
users that the color primaries value was not accurate and could lead
to incorrect transformations by post production tools.

I look forward to discussing this more in Berlin, and hopefully we can
rally enough troops to fund the development that can resolve this
issue.

Best,

Kieran.

---------- Forwarded message ----------
From: Kieran O Leary <[email-masked]>
Date: Fri, Jul 15, 2016 at 6:09 PM
Subject: Re: FFV1 and DPX

P.S
I'm attaching six images. - The thing to watch out for is what's in
the actual color transformation box. not sure if this will be of any
help.

 DPX
1. AVID source settings when importing Cineon profile LOG, but which
has no color primaries metadata flag - no LUT applied by default

FFV1->DPX
2. AVID source settings when importing that source DPX file after an
FFV1 transcode,  which has linear color primaries metadata flag -
Linear to rec 709 LUT applied by default
3. AVID source settings when default LUT has been removed -  image and
histogram looks identical (more thorough testing required) to the
source DPX window in image 1.

DPX
Log (Printing Density) file from Spirit (not as washed out as previous
example...)
a.  AVID source settings when importing Log/Printing Density , which
has Printing Density color primaries metadata flag - 2 Luts applied by
default - output is HORRIBLE
b.  AVID source settings when importing Log/Printing Density , which
has Printing Density color primaries metadata flag - Linear to rec 709
LUT applied by default

FFV1->DPX
c.  AVID source settings when importing DPX file after an ffv1
transcode , which has linear color primaries metadata flag - LUTS
removed
d. AVID source settings when default LUT has been removed -  image and
histogram looks identical (more thorough testing required) to the
source DPX window in image b.