Archived posting to the Leica Users Group, 2004/02/01

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Subject: [Leica] Re: Color accuracy
Date: Sun, 1 Feb 2004 17:44:38 EST

In a message dated 2/1/04 7:52:45 AM, 

<< I say color accuracy, but just yesterday, I found a color that not only  
film, but digital can't render right. I photographed a pariba  
tourmaline. The color is a very intense blue/green that is highly  
prized. Actually, you see the two colors depending on which angle the  
facets are in relation to the light. (We call it pleochroism.) The  
stone was nicely cut, no inclusions, and it was almost 7 carats - at  
about $20,000 per carat. Gorgeous. But I could NOT get my Canon D60 to  
get it right. And one of the best gem photographers doesn't seem to be  
able to do it with film either if any past photos I've seen are  
evidence. Photoshop at 16 bits couldn't get it right either, holding  
the stone up to the computer screen. The color is simply outside the  
gamut of any photographic process I have access to. >>

The trouble is that most chemical and electronic color processes use only 
three fixed colors to form an image. They are all based on the Young-Helmholtz 
theory of color vision that specifies that a minimum of three colors are 
necessary to specify colors. But there are some colors that the eye can visualize 
that lie outside the range embodied by the three primary colors incorporated in 
film layers or digital sensors. The human eye uses more than three types of 
color sensors - but then nature is not constrained by accountants or production 

Larry Z
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