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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: Rik Cabanier <cabanier@gmail.com>
Date: Tue, 5 Feb 2013 15:15:15 +1100
Message-ID: <CAGN7qDAji9J=BuX8aB_kRGNi4TsFLfite39O1gBNw1adQ=nKMA@mail.gmail.com>
To: Alan Gresley <alan@css-class.com>
Cc: Brad Kemper <brad.kemper@gmail.com>, Simon Fraser <smfr@me.com>, fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
On Tue, Feb 5, 2013 at 3:03 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?


Yes, that is correct except for the part where the gradient is transparent
in the middle :-)
So, yes, if you have a white background, they will look the same.
Received on Tuesday, 5 February 2013 04:15:42 GMT

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