[Bf-committers] Color to greyscale conversion - confusion

[Knapp]

On Mon, Jun 25, 2012 at 11:02 AM, Campbell Barton <ideasman42 at gmail.com> wrote:
> On Mon, Jun 25, 2012 at 10:44 AM, Knapp <magick.crow at gmail.com> wrote:
>> On Mon, Jun 25, 2012 at 10:19 AM, Campbell Barton <ideasman42 at gmail.com> wrote:
>>> On Sat, Jun 23, 2012 at 7:39 PM, Troy Sobotka <troy.sobotka at gmail.com> wrote:
>>>> On Jun 23, 2012 5:01 AM, "Campbell Barton" <ideasman42 at gmail.com> wrote:
>>>>
>>>>>
>>>>> - Texture and shading pipeline use rgb_to_bw() which treat RGB more
>>>>> evenly which might be better for shading when very un-even influences
>>>>> for RGB channels could be problematic for shading with textures of
>>>>> different colors (rgb_to_bw)
>>>>>
>>>>> - Where as with compositing - perceptual rgb->bw is much more
>>>>> important (rgb_to_grayscale)
>>>> g list
>>>>
>>>> Technically this is in the domain of LUTs once OCIO lands.
>>>>
>>>> The problem with attempting a non color aware approach is that it takes us
>>>> directly into the hard coded color domain again, as all values are assumed
>>>> 1:1 linear sRGB.
>>>>
>>>> With respect,
>>>> TJS
>>>
>>> Don't think lack of OCIO is an excuse for arbitrary/different hard
>>> coded conversions in our code.
>>> Will add comments to these functions to say we don't know why they are
>>> different and someone who has a clue could clear up the confusion one
>>> of these days :S
>>
>> That makes no sense to me. When is this person going to show up? What
>> makes you think he will ever come? Best to find the answer now and not
>> incur any more debt.
>
> That was the purpose of this thread, since nobody knows - we better at
> least document that this is a mystery so anyone reading the code is
> aware,
> this doesn't incur technical debt - it just exposes it.
>
> See:
> http://projects.blender.org/scm/viewvc.php/trunk/blender/source/blender/blenlib/intern/math_color_inline.c?root=bf-blender&r1=48259&r2=48258&pathrev=48259
>
> --
> - Campbell

I am never against documenting but we have found a problem. Why not
find the answer?

Really I can't see any reason not to go with the visual space way and
I would go with the GIMP way so that the users can assume a standard
way exists and be right at least partly. I can see no reason not to go
with one standard that looks good. I don't have a deep understanding
of this but it would seem that there is only one reason to go from
color to grayscale; so it looks good.

-- 
Douglas E Knapp

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