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Re: [css4-images] Non-linear interpolation between gradient color stops

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 21 Jan 2015 09:33:39 -0800
Message-ID: <CAAWBYDB1XvYb05UhqwYufjjSLrMYi3dfX=YuxqjX=fBj065nmA@mail.gmail.com>
To: Jonathan Rimmer <jon.rimmer@gmail.com>
Cc: www-style list <www-style@w3.org>
On Wed, Jan 21, 2015 at 7:16 AM, Jonathan Rimmer <jon.rimmer@gmail.com> wrote:
> I was reading the Gradient Color-Stops section of the ED for images level
> 4[1]. It seems to me that, even with the proposed color interpolation hint,
> gradients are still underpowered for creating smooth and aesthetically
> satisfying gradients, of the kind produced by tools like Photoshop, or in
> natural phenomenon such as sunsets.
>
> When an interpolation hint is provided, it only lets the author move the
> position of the mid-point between two color stops. All the interpolation
> between color stops and to and from the mid-point is still done linearly.
> Therefore, this does not address the problem that linearly interpolating
> through RGB color space will not produce perceptually uniform transitions,
> and can produce ugly transitions at the intermediate stops.
>
> A solution to this to allow non-linear interpolation between color stops.
> Photoshop's "smoothness" option provides the ability to smooth out
> transitions, apparently by using cardinal splines to interpolate between the
> points[2]. Here is a comparison between the unsmoothed red->white->blue
> gradient used as an example in the ED -- charitably described by the spec as
> "nice" -- and one produced in Photoshop using 100% smoothness:

This is already allowed.  The color-stop section is way too longer and
needs better organization, I admit, but if you start from the
paragraph starting with "By default, this interpolation is linear",
you'll find the description of how color hints affect interpolation.
It is absolutely not linear.  The formula used comes from Adobe, so I
assume it matches what Photoshop does, or something like that.

~TJ
Received on Wednesday, 21 January 2015 17:34:26 UTC

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