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Re: [OM] Tetrachromacy

Subject: Re: [OM] Tetrachromacy
From: JOHN DUGGAN via olympus <olympus@xxxxxxxxxxxxxxxxx>
Date: Mon, 29 Oct 2018 19:47:20 +0000 (UTC)
Cc: JOHN DUGGAN <john.duggan10@xxxxxxxxxxxxxx>
Bit of a grey area eh Ken. 😎

Regards  John Duggan,     Wales, UK

--------------------------------------------
On Mon, 29/10/18, Ken Norton <ken@xxxxxxxxxxx> wrote:

 Subject: Re: [OM] Tetrachromacy
 To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
 Date: Monday, 29 October, 2018, 18:33
 
 > It’s interesting to me
 because I lecture on vision as part of my job, and to day
 I’ve spoken only about rods and cones (and photo-sensitive
 ganglion cells), never about the 3-colour properties of most
 people’s cone cells.  And now I know that there are
 people with 4-colour cells.
 
 Several years ago I did quite a bit of research
 into this. The people
 with four-color (not
 colour) cones are rare enough to not be
 considered part of the normal human race. :) 
 HOWEVER, there are
 people who have rods with
 some pigment.
 
 It's
 pretty fascinating that the human eye does not actually
 "see"
 red. The red cones see a
 wide band of color from red down to yellow.
 This band is overlapped by the green cones. To
 determine "red", the
 human vision
 system sees the absence of green. So if the eye sees
 green and red, it's actually yellow/orange.
 If it sees red but not
 green, then it's
 actually red.
 
 This is very
 different than most digital sensors that traditionally
 have had pretty narrow-band filters with little
 overlap between blue,
 green and red sensels.
 Canon sensors are very wide-band with a thin
 pigment. The color accuracy is secondary to
 dynamic range. Color is
 determined by the
 same method as the human eye - using
 "mix-minus"
 calculations. (done
 on-chip at time of exposure, pre-raw). The Kodak
 sensors used a very deep filter that preserved
 color accuracy, but at
 the expense of
 bit-depth and sensitivity.
 
 Not much of that matters to me at the moment.
 Everything is monochrome
 in Alaska now.
 
 AG Schnozz
 --
 
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