[Tig] color vision (article)

[Arnell Patscott]

Along the lines of this thread, I wanted to point out that in the March issue of Scientific American there is a paper on Illusory Color and the Brain. They make the point that images that start out as color, and are turned B&W loose quite a bit of the image, more than just color. They also state that color is not separate from shape recognition, but very much a part of it. 

The article goes from the rods and cones to the brain centers responsible for interpreting them.
There is a small preview of the article at 
http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=CBDAEF3D-E7F2-99DF-3BA6019D1B7D1E08

but to see the whole thing, including diagrams of false color and brightness, you either have to buy the online version, or get the March 07 edition. 
I highly recommend it as ground breaking work on human color perception. 

Arnell Patscott

(No I do not work for Scientific American)

-----Original message-----
From: Jim Houston jdhouston at earthlink.net
Date: Mon, 19 Mar 2007 18:38:23 -0500
To: Rob Lingelbach rob at colorist.org
Subject: Re: [Tig] color vision

> Thanks to Cintel International for support in 2007.  http://www.colorist.org/wiki3
> ====
> 
> 
>  
> 
> On Mar 19, 2007, at 2:29 PM, Rob Lingelbach wrote:
> >
> > This isn't the explanation I was looking for regarding the need for  
> > extra
> > contrast after subtracting color from an image...
> 
> The vision explanation for this effect is that there are three types of
> cones involved in color vision and they combine in different ways
> to produce an internal  luminance channel, plus a red-green, and a  
> blue-yellow
> opponent color channels.   The perception of contrast is the combined
> signal from the luminance channel *and* the red-green and blue-yellow  
> channels.
> In practice, the blue-yellow has so little influence that it is  
> ignored. (think about
> how either blue or yellow text of equal luminance on a white background
> are equally hard to read.)
> 
> So contrast mostly comes from the perception of the luminance and
> the red-green channel.   If you remove the red-green channel  
> information,
> then you are only left with a portion (say about 70%) of the contrast  
> information the
> brain depends on, thus the image looks like it has less contrast.
> Boosting the gradient of the luminance of the image by 30% or so  
> restores
> much of the appearance of the image under the same viewing conditions.
> 
> These are human visual system effects that are independent of whether  
> it is on film
> projected in a dark room, or on a bright screen.
> 
> Jim H.
> Starwatcher Digital
> 
> 
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