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Re: Compositing math in SVG

From: Kai-Uwe Behrmann <ku.b@gmx.de>
Date: Mon, 16 Jul 2012 08:09:46 +0200 (CEST)
To: Rik Cabanier <cabanier@gmail.com>
cc: Kai-Uwe Behrmann <ku.b@gmx.de>, Calculemus <calculemus1988@gmail.com>, www-svg@w3.org
Message-ID: <alpine.LNX.2.00.1207160750380.8781@siras.rasena>
Am 15.07.12, 19:22 -0700 schrieb Rik Cabanier:
> On Sat, Jul 14, 2012 at 1:14 AM, Kai-Uwe Behrmann <ku.b@gmx.de> wrote:
>> Rik Cabanier <cabanier@gmail.com> schrieb:
>>> On Fri, Jul 13, 2012 at 10:36 AM, Calculemus
>>> <calculemus1988@gmail.com>wrote:
>>> When you blending 2 images, you need to make sure that they are in the
>>> same
>>> colorspace (aka the blending colorspace).
>>> If they are, I think you can just apply the blending formula's to the
>>> raw
>>> values. (1 in the blending formulas represents the maximum value of the
>>> your colorspace).
>>> If they are not, or the colorspace has no maximum/minimum values, you
>>> will
>>> need to convert to a wide gamut colorspace, blend in that and then
>>> convert
>>> back.
>> You can of course us a logarythmic function or a tone mapping op, which
>> looks much better than per channel clipping. The later one easily causes
>> not so nice colour casts.
> If your colorspace is wide enough there should not be any clipping. Make
> sure it is a wide gamut RGB if you want the same blending.
> Blending in CMYK or Lab looks very different for the same blend mode.

Any colour space can hold values over white and thus will expose artifacts 
for those over white colour values, if plain per channel clipping is 

Here a additive blending example with a colour perception error:
RGB 0.75,0.5,0.0 +    (warm earthy yellow)
RGB 0.75,0.5,0.0 =>   ( " )
RGB 1.5,1.0,0.0       (emitting orange, not displayable on paper/LCD)

after per channel clipping the result is a
RGB 1.0,1.0,0.0       (yellow)

kind regards
Received on Monday, 16 July 2012 06:13:48 UTC

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