Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB

[Elle Stone]

On 02/23/2015 02:42 PM, Kai-Uwe Behrmann wrote:
> LCMS is just one CMM, with its prefered set of min and maximal values
> for certain colour spaces. I could never find it convincing to have
> CIE*L expressed in % in LCMS, the same goes for Cmyk - a printing space.
> But LCMS uses these fixed value ranges from inbuild defaults.

I'm not sure what you mean by "fixed value ranges from inbuild defaults".

Since LCMS version 2 there is no clipping during conversions from RGB to 
LAB, XYZ, or another RGB color space. There's also no clipping upon 
export as long as the file format can hold 32-bit floating point RGB 
values outside the range 0-1 floating point.

The only limitation on these "unbounded" LCMS2 ICC profile conversions 
is the profile tone reproduction curve. It has to allow unambiguous 
extrapolation below zero and above 1.

GIMP 2.9 can import, create, and export 32-bit floating point tiffs with 
RGB values much greater than 1.0, and also less than zero if such values 
have been created during ICC profile conversions or editing.

Of course there are precision limitations on how high those 32-bit 
floating point tiff values can go before there's too little precision 
for useful image editing, though I don't know where the line should be 
drawn.

Are there differences in the number of stops that can be held in 32-bit 
floating point tiffs vs 32-bit floating point OpenEXR images?

Elle