On Sat, 2015-03-21 at 02:31 -0400, Martin Owens wrote:

This interesting video:

https://www.youtube.com/watch?v=LKnqECcg6Gw

If I'm remembering right, all open source tools use RGB average and suffer this same blending issue.

The video oversimplifies sRGB. There is an exponential section with an exponent of about 2.4 (there is an offset in the actual equation) along with a linear section. See:

https://en.wikipedia.org/wiki/SRGB

Some open source tools do get it right, at least partly. Gimp uses linear RGB when working with 16 bit images. Inkscape can use it for filters (although it is not the default).

It is a problem that is known about but getting Web browsers to see that it is an important problem isn't easy. I've brought it up several times in the SVG and CSS working groups. It effects scaling and gradients too. See:

http://tavmjong.free.fr/blog/?p=765 http://tavmjong.free.fr/SVG/COLOR_INTERPOLATION/index.html

What's the future look like for a solution?

SVG 1.1 has an attribute to set the blending color space to linear but nobody implements it (including Inkscape). Until the web browsers decide it is important, nothing will change in the web space. The example brought up in the video is quite nice though. I'll add it to my color interpolation page.

Tav

Martin,

On Sat, 2015-03-21 at 09:26 +0100, Jasper van de Gronde wrote:

On 2015-03-21 07:31, Martin Owens wrote:

...

This interesting video:

https://www.youtube.com/watch?v=LKnqECcg6Gw

If I'm remembering right, all open source tools use RGB average and suffer this same blending issue.

What's the future look like for a solution?

The future is here :) Using linearRGB rather than sRGB in SVG does precisely what is suggested in that video. Historically, Inkscape did not support this at all, but the most recent version started to support this using the color-interpolation-filters property: http://tavmjong.free.fr/blog/?p=765

Unfortunately, actually using filters for blending isn't easy. It can be done as shown in the attached file (viewable in Inkscape or Chrome but not in Firefox).

Tav