W3C home > Mailing lists > Public > www-svg@w3.org > July 2012

Re: Compositing math in SVG

From: Kai-Uwe Behrmann <ku.b@gmx.de>
Date: Sat, 14 Jul 2012 15:20:34 +0200
To: Calculemus <calculemus1988@gmail.com>
CC: Rik Cabanier <cabanier@gmail.com>,www-svg@w3.org
Message-ID: <e0395f2c-3f4a-484a-aeba-42c3a3882f2b@email.android.com>
Calculemus <calculemus1988@gmail.com> schrieb:

>Kai-Uwe Behrmann,
>
>1. "Clamping should always be the last step to preserve the HDR 
>as long as possible during processing. HDR highlights behave other than
>flat LDR white while compositing."
>
>Should clamping also be the last step for non-HDR too?
>For example, I have this code for color burn:
>
>1 - min (1.0f, (1-a)/b)
>
>should it be instead:
>
>clamp (1 - 1.0f, (1-a)/b, 0, 1)

Not sure if working with pseudo HDR values makes that much sense.
Would need some tests beforehand.

>2. "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."
>
>Hmm I would like to hear more about this, can you point me to
>some other sources that talk about this in more detail?

A search for "logarithmic tonemapping" brings some results.
And you could look on how OpenEXR performs tonemapping in its viewers.
www.openexr.org

>3. A question I have is, do you think I should have separate
>functions for each blend mode, for HDR and non-HDR?
>Or can HDR and non-HDR both be handled by one
>function for a blend mode?

kind regards
Kai-Uwe
Received on Saturday, 14 July 2012 13:17:29 GMT

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