Re: [css3-transitions] colour space used for colour interpolations

On Thu, May 24, 2012 at 11:47 PM, Tab Atkins Jr. <jackalmage@gmail.com>wrote:

> On Thu, May 24, 2012 at 9:44 AM, Rik Cabanier <cabanier@gmail.com> wrote:
> > Reading a bit more on the wikipedia article [1] on HSL, I came across the
> > following quote:
> >
> > Because hue is a circular quantity, represented numerically with a
> > discontinuity at 360°, it is difficult to use in statistical
> computations or
> > quantitative comparisons: analysis requires the use of circular
> statistics.
> > Furthermore, hue is defined piecewise, in 60° chunks, where the
> relationship
> > of lightness, value, and chroma to R, G, and B depends on the hue chunk
> in
> > question. This definition introduces discontinuities, corners which can
> > plainly be seen in horizontal slices of HSL or HSV.
> >
> > I believe it doesn't make sense to transition in HSL because of these
> issue.
> > Who would want to create such a synthetic transition?
>
> Heh, who would ever want to transition in RGB?  It's infinitely worse. ^_^
>

How so?


>
> Ultimately, what matters is what the system graphics libraries
> support, or can be extended to support.  HSL is a pretty shitty
> colorspace, but it's simple to work with, and way better than RGB for
> most things.  If we can convince the implementors working on graphics
> to do a better colorspace, awesome, but if we can't, falling back to
> HSL is acceptable in my mind.
>

Even though we offer HSL as an option in our apps, interpolation is always
done in the native colorspace (RGB or CMYK).
So, I feel that it's a little odd that you transition through the hues.


>
> (The major problem with HSL, more than anything else, is that there's
> no analog of "premultiplied" colors like RGBA has, so transitions
> to/from 'transparent' are going to be ugly.  I don't think any of the
> better colorspaces have a solution to this either.)


Split out the alpha. Then transition RGB and alpha separately and reapply
the alpha on the transitioned colors.
This is how we do it in InDesign, Illustrator and Photoshop and I haven't
heard of any complaints about quality.

Rik