[Openicc] beyond 8-bit precission [was: new version of xcalib]

[Bob Friesenhahn]

I should mention that while display technologies currently operate 
using absolute values, the human eye perceives the world based on the 
average and max/min brightess levels in the viewing environment.  Due 
to this we are able to drive our cars both during the day, and at 
night.  In order to adequately view very bright or very dark scenes on 
our computer displays which are used in rooms with typical brightness 
(usually display brightness/contrast is adjusted to suit the room), we 
must artificially adjust intensity values into the ideal range of the 
display device.  It does not work to view a scene taken at night in a 
similarly darkened room since the display device does not have the 
resolving power (or range) to handle that.  The night scene is 
therefore shown much brighter than it originally was, but this is 
offset by the human tendency to view an object based on the brightness 
surrounding it, and the average brightness of the overall picture.

The upshot of this is that discussions of absolute dynamic range are 
almost meaningless for computer users as long as the display device 
provides sufficient brightness and dynamic range to satisfy the range 
of human vision in the viewing environment.  Most images have already 
been adjusted (or may be adjusted) to suit the average display (sRGB).

Theater is a different situation since the average brightness of the 
film is primarily selected by the film's producer so that "Dark City" 
presents different display challenges than does "Snow Day".  In this 
case it is necessary to use more bits so that key intensity 
information is not lost.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/