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Re: [Public WebGL] The Newly Expanded Color Space Issue
- To: Steve Baker <email@example.com>
- Subject: Re: [Public WebGL] The Newly Expanded Color Space Issue
- From: Thatcher Ulrich <firstname.lastname@example.org>
- Date: Tue, 7 Sep 2010 19:53:58 +0200
- Cc: Chris Marrin <email@example.com>, public webgl <firstname.lastname@example.org>
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On Tue, Sep 7, 2010 at 7:19 PM, Steve Baker <firstname.lastname@example.org> wrote:
> I think we have to take this one teeny-tiny step at a time. First, let
> us establish once and for all what color space GLSL shaders operate in.
> Those of us who think that the color space of WebGL shaders can be
> anything other than linear...please convince me that you are right by
> clearly answering the following three blindingly simple and eminently
> practical questions.
> If you are right, then the answers should be easy, clear, intuitive and
> (above all) correct.
> Suppose I want a 50% blend between two images, or to make it
> super-simple: a 50% blend between a black texel and a white texel.
> That's a good choice of example since (0,0,0) and (1,1,1) are black
> and white, respectively, in both linear and sRGB space - so we don't
> have to concern ourselves with the thorny question of what the input
> texture color space is. Here are three ways I could get 50/50
> blend of two colors:
> QUESTION 1:
> In a linear space GLSL, I could write:
> x.rgb = mix ( vec3(0,0,0), vec3(1,1,1), 0.5 ) ;
> (Just to save you looking it up, the OrangeBook says that mix(x,y,a)
> returns "(x*(1-a)+y*a), ie the linear blend of x and y" - those are
> the exact words at the very top of page 124 of my early edition -
> and that is what every single GPU on the entire planet actually does).
> In my world, x.rgb will be (0.5,0.5,0.5) - which (with what I'm
> proposing) will automatically become pow(vec3(0.5,0.5,0.5),1.0/2.2)
> when it's composited into the frame buffer to produce the
> perceptually (and mathematically) correct result: (0.73,0.73,0.73).
Um... 0.73 in an sRGB frame buffer is (perceptually) 73% gray. Right?
I can't tell from the way you phrased the question whether 73% gray
is the wrong or right answer.
Are you asking for a result where the monitor emits 50% of the photons
of pure white, or a result that looks half as bright as pure white?
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