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From: | Elle Stone |
Subject: | Re: [Openexr-devel] OpenEXR files with nonlinearly encoded RGB |
Date: | Fri, 27 Feb 2015 09:44:17 -0500 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
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
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