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[filters] what should feGaussianBlur sample outside the source image?

From: Cameron McCormack <cam@mcc.id.au>
Date: Tue, 07 Aug 2012 10:27:17 +1000
Message-ID: <502060E5.3030100@mcc.id.au>
To: FX Taskforce <public-fx@w3.org>
CC: Robert Longson <longsonr@gmail.com>
Consider this document:

   http://people.mozilla.org/~cmccormack/tests/blur.svg

The Filters spec (and SVG before it) says the following in the 
feGaussianBlur section:

   If the input has infinite extent and is constant (e.g FillPaint,
   this operation has no effect.

The document uses FillPaint as the input to feGaussianBlur, but in Opera 
at least, the blue rectangular area has blurry edges, because it is 
(presumably) sampling transparent black outside the source image area. 
For the operation to have no effect, you would expect the rectangle to 
have sharp edges, which would imply sampling the FillPaint outside the 
source image area.

The test 
http://dev.w3.org/SVG/profiles/1.1F2/test/harness/htmlObjectMiniApproved/filters-overview-01-b.html 
seems to assume that transparent black is sampled outside the source 
image area.

The spec should be clarified to indicate how to sample around the edges 
of the source image, and if it should be transparent black, the sentence 
about having no effect with FillPaint should be changed.
Received on Tuesday, 7 August 2012 00:27:54 GMT

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