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Mention that getImageData() might return different pixel data than you set, due to premultiplying. (whatwg r3230)

From: poot <cvsmail@w3.org>
Date: Sat, 13 Jun 2009 03:45:19 +0900 (JST)
To: public-html-diffs@w3.org
Message-Id: <20090612184519.47B512BC3B@toro.w3.mag.keio.ac.jp>
Mention that getImageData() might return different pixel data than you
set, due to premultiplying. (whatwg r3230)

http://dev.w3.org/cvsweb/html5/spec/Overview.html?r1=1.2378&r2=1.2379&f=h
http://html5.org/tools/web-apps-tracker?from=3229&to=3230

===================================================================
RCS file: /sources/public/html5/spec/Overview.html,v
retrieving revision 1.2378
retrieving revision 1.2379
diff -u -d -r1.2378 -r1.2379
--- Overview.html	12 Jun 2009 07:49:58 -0000	1.2378
+++ Overview.html	12 Jun 2009 18:44:54 -0000	1.2379
@@ -22606,6 +22606,12 @@
   for all of the <code title="dom-context-2d-getImageData"><a href="#dom-context-2d-getimagedata">createImageData()</a></code>, <code title="dom-context-2d-getImageData"><a href="#dom-context-2d-getimagedata">getImageData()</a></code> and <code title="dom-context-2d-putImageData"><a href="#dom-context-2d-putimagedata">putImageData()</a></code>
   operations.</p>
 
+  <p class="note">Due to the lossy nature of converting to and from
+  premultiplied alpha color values, pixels that have just been set
+  using <code title="dom-context-2d-putImageData"><a href="#dom-context-2d-putimagedata">putImageData()</a></code> might be
+  returned to an equivalent <code title="dom-context-2d-getImageData"><a href="#dom-context-2d-getimagedata">getImageData()</a></code> as
+  different values.</p>
+
   <p>The current path, <a href="#transformations" title="dom-context-2d-transformation">transformation matrix</a>,
   <a href="#shadows" title="shadows">shadow attributes</a>, <a href="#dom-context-2d-globalalpha" title="dom-context-2d-globalAlpha">global alpha</a>, the <a href="#clipping-region" title="clipping region">clipping region</a>, and <a href="#dom-context-2d-globalcompositeoperation" title="dom-context-2d-globalCompositeOperation">global composition
   operator</a> must not affect the <code title="dom-context-2d-getImageData"><a href="#dom-context-2d-getimagedata">getImageData()</a></code> and <code title="dom-context-2d-putImageData"><a href="#dom-context-2d-putimagedata">putImageData()</a></code>
Received on Friday, 12 June 2009 18:45:51 UTC

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