Re: specifying colors outside srgb gamut with extended-linear-srgb

Yes, I agree with Lea.

Intuitive would be pure appearance attributes such as lightness/brightness, hue, colorfulness.

Something that a 9-year old can understand.


Most color experts have had their minds corrupted with encoding technologies and lost the connection to intuitiveness.

But even for color experts, negative RGB values are often non-intuitive. Most grading tools don’t support negative values at all or well. And ACES blue primary has negative luminance, so adding blue makes the image darker. Not intuitive for the colorist.




From: Lea Verou <>
Date: Tuesday, June 8, 2021 at 12:06 AM
To: Mike Smith <>
Cc: "" <>
Subject: Re: specifying colors outside srgb gamut with extended-linear-srgb
Resent-From: <>
Resent-Date: Tuesday, June 8, 2021 at 12:05 AM


I don’t think any cartesian color model, and especially anything RGB-based is "intuitive". That's what polar color models are for (LCH, JzCzHz etc), which more closely match the way humans think about color.

IMO extended sRGB is primarily useful as a translation space, not for humans to specify directly, negative coordinates or not.


Lea Verou

👩🏽 (she/her)


Web standards (W3C TAG, CSS WG), Usability research (MIT CSAIL), Open Source



🐦 @leaverou




On Jun 8, 2021, at 08:32, Michael Smith <> wrote:


Hi colorweb members.

Using extended-linear-srgb seems intuitive when colors are inside sRGB gamut, if I want a yellow that is twice as bright as a regular bright sRGB yellow, I use (r,g,b)=(2,2,0) instead of (r,g,b)=(1,1,0).

What if I want my application to use a nice saturated BT.2020 yellow instead, which is out-of-sRGB gamut, for example (r,g,b)=(2,2,0) in BT.2020 linear would translate to (r,g,b)=(2.145699727, 2.016698845, -0.237459323) in extended-linear-srgb with a negative blue value. Do we really expect users to specify negative color values?  I'm concerned that will be non-intuitive to users without a color science background.  Or maybe we intend users to only feel comfortable with extended-linear-srgb when colors are inside sRGB gamut?



Received on Wednesday, 16 June 2021 03:18:57 UTC