Re: [Algorithms] RGB to XYZ conversion

[Wolfgang E. <wol...@gm...>]

The luminance transform for the tone mapper. With those numbers I can  
transform back and forth without visible quality loss on my hardware  
platform ... I can switch on and off the tone mapper and I would not  
see a difference with neutral tuning values. That is important for the  
artists as a starting point.

Sent from my iPhone

On Apr 21, 2008, at 10:34 AM, "Marco Salvi" <mar...@gm...> wrote:

> Umh..interesting, why did you use CIE XYZ for your post processing  
> pipeline?
>
> Regarding the original question: small variations in the colour  
> transform don't really make any significant difference
> if you are using CIE XYZ just to store your data in a different way  
> (ie HDR data in 4 bytes per pixel or less),
> as you have to go back to RGB to display your image anyway.
>
> While working on Heavenly Sword I played with slightly different  
> matrices and even artists
> couldn't notice any difference.
>
> Marco
>
> On Mon, Apr 21, 2008 at 10:24 AM, Wolfgang Engel <wol...@gm... 
> > wrote:
> I used this for PostFX. The equation I use is different from yours.
> The color values that go in there are already gamma 1.0.
> I posted my numbers on my blog
>
> Diaryofagraphicsprogrammer.blogspot.com
>
> I can't remember how I came up with them but it was probably not a
> scientific way.
>
> Sent from my iPhone
>
> On Apr 21, 2008, at 10:04 AM, chr...@pl...
> wrote:
>
> >
> > Dan Glastonbury wrote:
> >> Dear colour space experts
> >> What matrix should I being using to convert RGB values to CIE XYZ?
> >> Christer Ericson (http://realtimecollisiondetection.net/blog/?p=15)
> >> gives the following matrix:
> >>
> >>  M = [0.497,0.339,0.164]
> >>      [0.256,0.678,0.066]
> >>      [0.023,0.113,0.864]
> >>
> >> to be used in [X Y Z] = [R G B]*M and I assume this comes from Greg
> >> Ward's paper.  Charles Poynton's ColorFAQ and wikipedia's article  
> on
> >> CIE 1931 give different formulations for the conversion.
> >
> > Good question Dan, and I for one don't know the answer. I asked  
> myself
> > the same question when I wrote that blog post and first worked out  
> the
> > code. Everywhere you look, there's another subtly different matrix
> > given. As we didn't end up using any logluv encodings, I never tried
> > to find out what's the "correct" matrix. As you correctly assumed, I
> > just used the values given in Greg Ward's paper for the blog post.
> >
> >
> > Christer Ericson, Director of Tools and Technology
> > Sony Computer Entertainment, Santa Monica
> > http://realtimecollisiondetection.net/blog/
> >
> >
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