[Bf-vfx] Mango Samples with ACES via rrt_sRGB

[Ton Roosendaal]

Hi Brecht,

I've invited OpenColor (Jeremy Selan) to check on the F65 footage too. 

-Ton-

------------------------------------------------------------------------
Ton Roosendaal  Blender Foundation   ton at blender.org    www.blender.org
Blender Institute   Entrepotdok 57A  1018AD Amsterdam   The Netherlands

On 17 May, 2012, at 4:09, Brecht Van Lommel wrote:

> 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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