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Fractional pixel with background-size-022 and background-size-023; 2 problems with cat image

From: Gérard Talbot <css21testsuite@gtalbot.org>
Date: Tue, 14 May 2013 00:26:26 -0400
Message-ID: <5eb919c8ae80b1c4c2146dcc7d20e797.squirrel@ed-sh-cp3.entirelydigital.com>
To: Zhang@gtalbot.org, "Zhiqiang" <zhiqiang.zhang@intel.com>
Cc: "public-css-testsuite@w3.org" <public-css-testsuite@w3.org>
Zhiqiang Zhang,

http://test.csswg.org/suites/css3-background/nightly-unstable/html4/background-size-022.htm

http://test.csswg.org/suites/css3-background/nightly-unstable/html4/background-size-023.htm

There is a fractional pixel issue involved with those tests.


There seems to be 2 problems with the cat image:

1- it's 98px wide by 99px tall. So, rescaling such image (to 75px by
75px or to 80px by 80x) is bound to create a loss of a fraction of a
pixel or rounding of fraction of a pixel (or both) since the intrinsic
ratio of the image is not 1:1 but 98:99 . With Firefox 20 and Opera
12.15, the paws of the cats on the 2nd row are different (bottommost 1px
appears to be clipped) from the paws of the cats on first row (I see all
of the paws). This is not the result of a bug in those browsers but
rather the result of a not-so-good image for those tests.

2- The cat image has white areas on its 4 sides/edges; the cat image
does not fill the 98px by 99px area with a color different from white.
This can creates unexpected difficulties when checking for test failures
by humans.
In some tests, I remember that 1px from the cat tail was clipped due to
rounding down of fractional pixel.


I suggest to try to redo or adjust those 2 tests by using the

http://test.csswg.org/suites/css3-background/nightly-unstable/html4/support/100x100-blue-and-orange.png

because such image does not have those 2 problems; orange color has a
good contrast with regards to blue color and both blue color and orange
color constrast well with white color.

I have edited 1 Shepherd's file about this issue:

http://test.csswg.org/shepherd/testcase/background-size-023/#comment-f0111262e4f5

Gérard
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Received on Tuesday, 14 May 2013 04:26:57 UTC

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