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Re: Calculating Normal Map

From: MenTaLguY <mental@rydia.net>
Date: Wed, 3 May 2006 15:29:23 -0700
To: Mark McKay <mark@kitfox.com>
Cc: www-svg@w3.org
Message-ID: <325bbab97a6d6ed24f54a7bad0029246@localhost>

On Wed, 03 May 2006 16:07:12 -0400, Mark McKay <mark@kitfox.com> wrote:
> I'm trying to write a function that calculates a normal map from a bump
> map, and am using http://www.w3.org/TR/SVG/filters.html#feDiffuseLighting as a guide.
> Unfortunately, the normal calculation requires me to multiply by the
> function I(x, y), and nowhere defines what function I is.

I(x, y) is simply the alpha component of the filter input at x, y.

Think "I for input".  It wouldn't have hurt to have stated that explicitly in the table of names above the formula, however.

> How can I perform the Sobel gradient?  Also, why does the SVG Sobel
> calculation appear so much more complicated than other versions I google?

Most descriptions of Sobel don't explicitly specify how the special cases at the edges of the input are to be treated.

-mental
Received on Wednesday, 3 May 2006 22:29:32 GMT

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