[Bf-vfx] Mango Samples with ACES via rrt_sRGB

[Brecht Van Lommel]

Uploaded some more files from a street test:
http://download.blender.org/ftp/incoming/Mango/ocio-aces-to-rrt_srgb/

There's the EXR exported as S-Log/S-Linear/ACES, and conversion of
those files with ACES => RRT sRGB, and the S-Log file with the OCIO
S-Log spaces => RRT sRGB. I think this shows that we are not
accidentally applying an S-Log to sRGB transform. Also, letting OCIO
do the S-Log to sRGB conversion doesn't give the same results, but
it's slightly worse regarding dark shadows.

Regardless, it seems unlikely to me that the conversion to ACES in the
F65 software is wrong, it can't be that broken. It's also the most
well defined part of the conversion, there is no data loss here. It's
the ACES => sRGB transform that's tricky, where we need to fit a big
gamut into a smaller one, and artistic choices play a role.

And I'll ask if there color chart footage, hopefully they have it :)

Also as a sidenote, I found out a problem to solve for OpenColorIO usage:

* For the spi-vfx and aces configurations in OpenColorIO, the scene
linear to display sRGB transform is not invertible, it can only be
applied in one direction. Seems quite silly that you can't pick a
color and get it back exactly the same in a render.
* The aces configuration does not define good color spaces for
texture_paint/matte_paint/color_picking. The spi-vfx configuration
does but its scene linear space seems quite different than aces from a
quick test.

Brecht.

On Thu, May 17, 2012 at 3:04 AM, Troy Sobotka <troy.sobotka at gmail.com> wrote:
>
> On May 16, 2012 3:21 PM, "Brecht Van Lommel" <brechtvanlommel at pandora.be>
> wrote:
>>
>> I can't say that applying a 2.2 gamma makes the images look clearly
>> better to me.
>
> Hard to know, but they might be on the crunched side it seems.
>
> It is worth testing against log just in case.
>
> The obvious solution is to get a shot of the Macbeth chart he likely shot.
> From that, it will become extremely clear if we are in the ballpark. It is
> possible to even compare against the numerical ACES values once there.
>
>> The difficulty with this stuff
>> is, how to verify that the conversion we are doing is right, i.e.
>> neutral?
>
> See above.
>
> I will try a few tests tonight.
>
>>
>> If I understand this right, you propose to let OCIO do the S-Log to
>> ACES conversion instead of the F65 software, and see if the result is
>> different than converting to ACES there directly?
>
> Yes. I suspect there will be an SGamut DPX Log out?
>
>> Also, my understanding is that the F65 has three color temperature
>> settings: 3200k, 4300k and 5500k.
>
> It appears that only the tungsten and daylight LUTs are provided. Not sure
> what is going on under the hood.
>
> Regardless, the process is far ahead of where it started.
>
> Let's hope OCIO can find a much needed home within Blender during Mango...
>
> With respect,
> TJS
>
>
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