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Re: [CSS4 color][CSS4 transition] color pre-multiplied vs non pre-multiplied was (Re: [CSSWG] Minutes TPAC Tue 2012-10-30 AM I: Abstract Directions, Transforms, Transitions)

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 4 Feb 2013 20:52:39 -0800
Message-Id: <3B7B9AD0-28B8-4AF3-896B-9DC0DB6D5CE6@gmail.com>
Cc: Simon Fraser <smfr@me.com>, Rik Cabanier <cabanier@gmail.com>, fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
To: Alan Gresley <alan@css-class.com>
On Feb 4, 2013, at 8:03 PM, Alan Gresley <alan@css-class.com> wrote:

> On 5/02/2013 2:53 PM, Alan Gresley wrote:
> 
>> Brad. I'm just wondering what type of background you plan to use under
>> any gradient with alpha transparency?
>> 
>> A pre-multiplied gradient of yellow to transparent to blue is identical
>> to a non pre-multiplied gradient of yellow to transparent-white to blue
>> when composite on a white background. There is _no need_ for an extra
>> color stop.
> 
> Wrong and correction. A pre-multiplied gradient of yellow to transparent to blue compiste of a whitye background is identical to a gradient of yellow to white to blue (fully opaque).
> 
> What do you want to achieve with a gradient that has alpha transparency and have you tested any of this by observing the difference between pre-multiplied colorspace and non pre-multiplied colorspace?

As I recall, last time I had a problem with the way Safari does gradients, it was a solid color to transparent, and the stuff underneath it was variable, some white, some other colors. I just wanted the color to fade to transparent over the varied background, but instead it looked dirtier as it faded out.
Received on Tuesday, 5 February 2013 04:53:11 GMT

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