[webkit-dev] White PNG image with alpha problem

[David Hyatt]

We have an optimization for tiling of 1x1 background images to do a  
rect fill instead of drawing the image itself.

dave

On Nov 5, 2006, at 12:51 AM, Mike Fischer wrote:

> Hi Mitz,
>
>
> Am 05.11.2006 um 09:00 schrieb Mitz Pettel:
>
>> Hi Mike,
>>
>> I believe this is http://bugs.webkit.org/show_bug.cgi?id=3438 —  
>> incorrect display of transparent 1x1 PNGs.
>
> Indeed, that looks like a hit. Thanks!
>
>
>> Other than using canvas, you can specify a background color with  
>> alpha for the div, for example, style="background: rgba(255, 255,  
>> 255, 0.6)", use an opaque fill and the opacity property, or use a  
>> PNG with bigger dimensions.
>
> Hmm, good ideas. I'll have to check cross browser compatibility  
> though. (There are hacks for CANVAS in IE and transparent PNG in IE  
> 5.5 to pre 7.0 which I'm evaluating right now. But I don't know  
> about transparent colors in CSS. In Firefox 2.0 the CSS rgba color  
> specification does not seem to work so I guess that method is out.)
>
> The bigger PNG (1x2 Pixels) does indeed work in the released  
> Safari. And it's only one byte larger on disk than the 1 Pixel  
> version. So that is definitly a good workaround. I'd never have  
> expected the dimensions of an image to change the color  
> interpretation 8-)
>
>
> Thanks!
> Mike
>
>>
>> Cheers,
>> -- Mitz Pettel
>>
>> On Nov 5, 2006, at 9:40 AM, Mike Fischer wrote:
>>
>>> Sorry, I forgot to add a subject!
>>>
>>>
>>> Am 05.11.2006 um 08:35 schrieb Mike Fischer:
>>>
>>>> Hi!
>>>>
>>>> I am seeing a strange problem with transparent PNG files in the  
>>>> release version of Safari/WebKit on Max OS X 10.4.8 PPC:
>>>>
>>>> I created a 1 pixel PNG image with color white and an alpha  
>>>> value of approx. 60%.
>>>>
>>>> When I display this in an IMG tag (or as a CSS background image)  
>>>> over other content the other content does not appear lighter as  
>>>> expected but more gray (not really darker).
>>>>
>>>> When I use a CANVAS element to draw a white fill color with 60%  
>>>> alpha the background is lightened as expected.
>>>>
>>>> The current nightly build does not show this problem. By  
>>>> searching for bugs related to PNG on <http://bugs.webkit.org> I  
>>>> couldn't find anything relevant. Also Firefox 1.5.0.7+, Opera  
>>>> 9.02 and OmniWeb 5.5.1 show the expected color effect, i.e.  
>>>> lightening the background.
>>>>
>>>> OTOH using a 1 pixel PNG with color black and an alpha of 50%  
>>>> works exactly as expected, i.e. darkening the background for a  
>>>> shadow effect.
>>>>
>>>>
>>>> My questions:
>>>>
>>>> a) Was there a bug in WebKit causing this that got fixed for the  
>>>> current nightlies? Or is this some unintended side effect and I  
>>>> need to file a new bug to ensure that this stays fixed in the  
>>>> future?
>>>>
>>>> b) Is there a workaround for the released version of WebKit  
>>>> (419.3)? (Other than using a CANVAS element ;-)
>>>>
>>>>
>>>> A test page demonstrating the effect is here (the top  
>>>> transparent area shows the problem):
>>>> <http://home.fi-works.de/test/test-png-alpha.html>
>>>> Note that the testing area is built using JavaScript DOM methods  
>>>> in this example. It essentially builds three layers: At the  
>>>> bottom some text is created. Then (DIV id:"bgc1" z.index:1) some  
>>>> color areas are created and in the top layer (DIV id:"bgc2" z- 
>>>> index:2) the transparent testing areas are created.
>>>>
>>>>
>>>> Thanks!
>>>> Mike
>>>> -- 
>>>> Mike Fischer         Softwareentwicklung, EDV-Beratung
>>>>                                     Schulung, Vertrieb
>>>> Web: <http://homepage.mac.com/mike_fischer/index.html>
>>>>
>>>
>>> -- 
>>> Mike Fischer         Softwareentwicklung, EDV-Beratung
>>>                                     Schulung, Vertrieb
>>> Web: <http://homepage.mac.com/mike_fischer/index.html>
>>>
>>> _______________________________________________
>>> webkit-dev mailing list
>>> webkit-dev at opendarwin.org
>>> http://www.opendarwin.org/mailman/listinfo/webkit-dev
>>
>
> -- 
> Mike Fischer     Softwareentwicklung, EDV-Beratung
>                                 Schulung, Vertrieb
> Address: Bundesstrasse 9, D-20146 Hamburg, Germany
> Phone: +49 (0)40/45038886, Fax: +49 (0)40/45038887
>
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