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Re: Compositing math in SVG

From: Rik Cabanier <cabanier@gmail.com>
Date: Mon, 16 Jul 2012 11:58:00 -0700
Message-ID: <CAGN7qDA6YMh=Q8oZKnp5qZJOKm70gr-7NrrPd8fHbx=Rp57CXg@mail.gmail.com>
To: Kai-Uwe Behrmann <ku.b@gmx.de>
Cc: Calculemus <calculemus1988@gmail.com>, www-svg@w3.org
On Sun, Jul 15, 2012 at 11:09 PM, Kai-Uwe Behrmann <ku.b@gmx.de> wrote:

> 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
> deployed.
>
> 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)
>
>
Maybe this is why there is no 'add' in the list of blend modes and is a
compositing mode instead...
Received on Monday, 16 July 2012 18:58:28 GMT

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