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Re: [css3-color] ICC implementation

From: David Woolley <forums@david-woolley.me.uk>
Date: Sun, 31 Aug 2008 13:47:29 +0100
Message-ID: <48BA92E1.3070309@david-woolley.me.uk>
To: www-style@w3.org

Chris Murphy wrote:

> This is precisely why photographers are encouraged to "expose right" 
> meaning to the right side of a histogram, which are quarter tones and 
> highlights. It is preferable to correct in post-processing what appears 
> to be a slightly overexposed images. This results in a higher quality 
> capture.

In any system with quantisation, or other noise, I would have thought it 
was self evident that one should maximise the use of the dynamic range. 
  However, my experience is that digital media tolerate over-exposure 
very badly.  That I think is also self evident, as over-exposed values 
are hard clipped, whereas underexposure simply results in increased 
noise.  That isn't to say that quantisation noise isn't a problem with 
typical 8 bit storage formats.  In my experience, for amateur use, one, 
or even half a, stop over is unacceptable, whereas two stops under is 
still usable. (Most scenes have some small highlights that can 
reasonably be clipped, of course.)

Silver halide media doesn't clip hard, in the negative, when you 
over-expose.  I actually had a couple of photographs, on film, where I 
deliberately overexposed the surroundings, to bring out shadow, but the 
(mass market) lab corrected the image (and the scan to CD) with no real 
apparent degradation of the over-exposed bits.  On digital media, they 
would have been end stop white.  One was the same scene exposed for the 
sunset and for the building, and both looked about the same.  (In these 
cases, tbe lab's effective underexposure did bring up the noise to 
noticeable levels, when corrected digitally to the intended exposure.)

David Woolley
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Received on Sunday, 31 August 2008 12:48:06 UTC

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