Re: [Gimp-developer] Don't make an architectural mistake based on a groundless premise

[Elle Stone <ellestone ninedegreesbelow com>]

On 10/10/2014 05:01 PM, Simon Budig wrote:
> Elle Stone (ellestone ninedegreesbelow com) wrote:
> > You cannot get from "sRGB as PCS" to LAB without first converting from "sRGB
> > as PCS" to XYZ. LAB is a mathematical transform of XYZ, not sRGB.
> >
> > This is the normal path from User_RGB to LAB: User_RGB -> XYZ -> LAB. Two
> > conversions.
> >
> > You want to take this path, yes? User_RGB -> XYZ -> "sRGB as PCS" -> XYZ ->
> > LAB. Four conversions, going through XYZ twice.
>
> [I am most likely talking about stuff that you already know, but it
> might be worth reiterating to keep the discussion understandable for
> people not that deep in the topic]
>
> Note that - as long as we're talking about linear RGB spaces (which pure
> sRGB is not, but AFAIK we're talking about "linear RGB with the sRGB
> primaries" here) - all but the last conversions in your chain boil down
> to applying a matrix to a vector. You can easily multiply these matrices
> together to build a matrix that does the first three conversions in a
> single operation.

Simon, my apologies. Pippin has pointed out that I didn't repond to your 
email. Yes, I do realize that you can concantenate matrix conversions. I 
acknowledged that in a reply to Pippin, but I should also have 
acknowleged your input.

Again, my apologies. I didn't mean to ignore you.

Kind regards,
Elle Stone