[Gllug] FLOSS

[Chris Bell]

On Wed 05 Nov, Tethys wrote:
> 
> 
> John Hearns writes:
> 
> >Going off topic,
> >there is a fork of The Gimp called Cinepaint http://www.cinepaint.org
> 
> Interesting. I'd been wondering what had happened to Hollywood/Film Gimp.
> Looks like this is the answer... In the process, they've gone from Film
> Gimp's 16 bits per channel up to a staggering 32 bits (128 bits per pixel
> for full RGBA). I can't off the top of my head think of a use for that
> depth of colour, even to prevent rounding errors. It'll help when treating
> greyscale images as RGB, but little else. I mean, it gives around 2 x 10^22
> times more colour data than the human eye can process. That's quite a bit...
> 
> Tet
> 

   The problem is not the absolute range of brightness, the human eye has a
logarithmic response, an auto iris, and auto gain control. This is difficult
to match using linear techniques with computers.

   The response of the human eye to various light frequencies (colours) and
levels is complex, and varies between individuals, with about 10 percent
being very different from the average. The three colour sensors which give
us red, green, and blue, have a huge amount of overlap, and have
approximately logarithmic sensitivity. A tremendous amount of research went
in to the design of the analogue broadcast television system to get the best
compromise for gamma correction and cross-colour mixing using mathematical
matrix techniques, and this included compensation for the colour and gain
distortions (gamma) introduced by television picture tubes made to the
original standards.
   Computers normally use linear colour descriptions which are simple to use
but basically the wrong approach, and often ignore the strange colour
rendering and gamma of the screen display, while few screens are able to
display the full range of colours. The most difficult colours to display are
usually the extreme reds, and early TV tubes used expensive "rare earth"
compounds to give the best results, with extended red response. The eye and
brain can make compensations, but it must be a compromise.

-- 
Chris Bell


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