Re: [Gimp-developer] Attempt to summarize the discussion of my examples of what doesn't work in unbounded sRGB

[Øyvind Kolås <pippin gimp org>]

On Mon, Apr 21, 2014 at 1:16 PM, Elle Stone
<ellestone ninedegreesbelow com> wrote:
> On 04/21/2014 07:07 AM, Teo Mazars wrote:
> > Hmm, I understand, then the default black-to-white gradient would be non
> > perceptually linear, which is more surprising than the color-to-color
> > gradient. I think I am now convinced this is correct, but it will probably
> > be puzzling to use.
> >
> > BTW, "gradient" is not such a good example because it's not related to
> > chromaticities, "Invert" would be a better one.
>
> I don't understand what you are trying to say. How is drawing a gradient
> from most saturated red to most saturated green in any given color space not
> related to chromaticities?

Picking the gradient color stops (including start and end) colors can
be considered as separate from the color space the rendering process
and interpolation is done in.

> The color space chromaticities are what determine the most saturated
> possible colors in any given color space.
>
> Aren't the negative RGB values required to draw a gradient in unbounded mode
> sRGB from Rec. 2020 reddest red to Rec. 2020 greenest green exactly what
> makes the gradient so horribly wrong when drawn in perceptual rather than
> linear? It's the effect of the perceptual TRC that sends the "out of bounded
> sRGB gamut" colors to strange places.

This might be an argument that do the _interpolation_ by default in
for instance CIE Lab instead of sRGB.

/pippin