Re: [Openexr-devel] Blender + OpenEXR

[Bob Friesenhahn]

On Fri, 3 Mar 2006, Kai-Uwe Behrmann wrote:

> ask Bob Friesenhahn. He has the probably best dpx/cineon implementation
> out there in GraphicsMagic including the 16-bit colour management via lcms
> on the output side.

I am interested in the answer so I am listening. :-)

The more I learn about color management for film, the more I see how 
ICC CMS does not adequately address the current methods.  There is a 
bunch of magic employed, but it always seems to include a viewing LUT 
(e.g. to a Rec.709 calibrated monitor) which maps the film colors to 
the display.  So the data is output referenced after it has been 
graded.  If the viewing monitor can not be sufficiently well 
calibrated by itself, then an extra black box can be used to convert 
the SDI data so that correct colors are displayed for Rec.709 input.

For DCI digital cinema, colors are expressed in XYZ space so they are 
absolute and don't use a LUT.  But a LUT is necessary to transform 
from the film colorspace into XYZ space for the DCI master.  In this 
case, Rec.709 is the reference point to make that possible since the 
work is graded on a Rec.709 monitor.  So ICC CMS could be used to 
implement the translation.

MPEG digital cinema is presumably Rec.709 and can use the same LUT as 
was used for viewing on a Rec.709 display except that the data has to 
be transformed into Rec.709 for delivery rather than just viewed 
through a LUT.

Lastly, DVDs are presumably in Rec.601 space which is yet another LUT. 
This could be handled via a simple ICC CMS transform, but it is also 
likely that the colorist will want to make additional adjustments 
based on what he sees in the output or based on experience.

None of the above includes OpenEXR which yet another variable to the 
mix.

The elephant in the closet is that since Rec.709 is the standard, it 
is impossible to properly evaluate colors which fall outside 
of the Rec.709 gammut.

If I have gotten anything wrong, please feel free to correct me.

Bob
======================================
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/