[Bf-committers] Color Balance & Color wheel issue

[Xavier Thomas]

My suggestion here is to use a more flexible color management
workflow: Have some predefined LUTs for gamma correction (sRGB, linear
(no change), log, ...) and for each image, node input or sequencer
strip we should have the ability to set the color space. So the user
can tel the image is in linear color space even if it is not and there
will be no conversion. Of course having the ability to add/customize
the LUTs and to automatically set 8bit image to sRGB and float to
linear would be even better. And even better would be to merge this
with the swscale operation that already does color-space
transformation (YcbCr to RGB with gamma correction) for most movie
files. Also the image viewer and scopes should have their own LUTs
too.

I spoke of this once with Matt and we decided to take some time to
make a design proposal together after the feature freeze and when he
will have time.

I remember he wasn't really happy with the 32bit float support of the
open-sources CMS but lcms2 got released soon after his tests and seems
to correct that issue.

Also using a CMS for mostly doing gamma correction seems a little
overkill but lcms is really light and maybe could allow to use custom
color profiles in the future.

Back on the Lift gamma gain issue I think it is better to assume that
every images/buffers in the compositor are in linear color-space and
there must be a way to use some logarithmic mapping that works well
for the UI controls. Personally I like when the numerical value input
correspond to the real mathematical value underneath, so I can set my
black/white level easily by using the color picker and copying
directly the values in the lift/gain UI controls but I suppose artists
works differently then engineer on this one.

It also might be good to take inspiration of the grade tool in nuke
which is awesome and works in linear color-space.


Xavier

2010/7/20 François T. <francoistarlier at gmail.com>:
> Hi,
>
> FYI here is what I asked to Stu Maschwitz (colorista guy) on twitter :
>
> "- @5tu <http://twitter.com/5tu> is there a reason why Lift in colorista is
> crunching pretty fast w/ linear enable in AE ?
> - @francoisgfx Yes, lift will crunch hard in linear. Colorista is designed
> to work on gamma-encoded images."
>
> As Sebastian König point out on twitter through this screenshot (
> https://dl-web.dropbox.com/s/ex9ec02gnil4vz0/color-management-woes.jpg),
> when gamma corrected the Color Balance behave correctly. Which make since
> since Stu says L/G/G is design to work in non-linear space and that
> Sebastian operation in CM mode bring the input back to non-linear.
>
> The question is shouldn't we do gamma correction in CB node in case CM is
> active ? I'm not sure what repercussion it could have on inputs and stuff.
> The idea would be to reproduce the setup Sebastian did directly in the code
> in case of CM otherwise leave it as it is.
> Maybe that's what your modification does Campbell because I'm not sure
> Sebastian where using the last build, but I still don't have the same value
> in both case (CM & not CM).
>
>
> Cheers,
>
>
> François,
>
>
>
> 2010/7/20 <bf-committers-request at blender.org>
>
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Mon, 19 Jul 2010 21:45:11 +0200
>> From: Fran?ois T. <francoistarlier at gmail.com>
>> Subject: [Bf-committers] Color Balance & Color wheel issue
>> To: bf-committers at blender.org
>> Message-ID:
>>        <AANLkTinh1beokGXTZjkiQgYMYSRKJUuDdkS0_nAbAs_w at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> Hey guys,
>>
>> I've been trying to play with Color Balance since the new changes, but I
>> believe a few things are acting weird (or at least differently than Magic
>> Bullet Looks (MBL), and as I read it is supposed to behave more likely.
>> Also
>> a few issues with the Color wheel.
>>
>>
>> First of all the Color Wheel :
>> - it is really jerky (not smooth)
>> - the brightness sidebar is affected (doesn't do that in MBL)
>> - brightness only go up to 2 (I believe MBL is 10)
>> - cubic color selection is something good, but since the second
>> modification
>> to it, it does feel less natural
>> - releasing the color wheel do not move the mouse to the new position,
>> which
>> make fine tuning from this release point very hard
>>
>> but I must say the finest selection with SHIFT is awesome :)
>>
>>
>> for the Color Balance part, I don't quite understand what as been change? I
>> did some test before with the exact same value on both side (AE MBL &
>> Blender's Color Balance) and I had the exact same result. As far as I was
>> setting both with the same Color space environment (linear or non-linear).
>> I didn't push the test as far as before, but it doesn't feel the same, I
>> can't quite understand what it is yet but it's feeling funny. Am I the only
>> one having this sensation ?
>>
>>
>> cheers
>>
>>
>>
>> --
>> ____________________
>> Fran?ois Tarlier
>> www.francois-tarlier.com
>> www.linkedin.com/in/francoistarlier
>>
>>
>>
>
>
> --
> ____________________
> François Tarlier
> www.francois-tarlier.com
> www.linkedin.com/in/francoistarlier
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