Re: Colour blindness [Was: Re: "Shared" procedure division code]

A very interesting analogy with computer technology. Not sure how accurate
it is, but it sounds plausible...

Pete.

TOP POST.
"Oliver Wong" <owong@castortech.com> wrote in message
news:O6rKe.173554$9A2.118337@edtnps89...
>
>
> "Pete Dashwood" <dashwood@enternet.co.nz> wrote in message
> news:3lu3t5F14com8U1@individual.net... 
>
>    I'm not colour blind (as far as I know), but my understanding of
> red/green colour-blindness is that it results from the red light and green
> light receptors in one's eyes being indistinguishable to their brain.
>
>    That is to say, typically a person's eyes has three kinds of receptors,
> one for measuring brightness of red, green and blue light respectively.
> Also, typically the brain can tell which signal is coming from which type
> of receptor, and is able to use this information to build a 3 channeled
> (RGB) image in their mind.
>
>    If the brain can't differentiate between the red receptor and the green
> receptor, then I'd imagine it'd be like taking an RGB image and, for every
> pixel, replacing the values of R and G with the average of those two
> values. So if a pixel had the value (2,4,6), for example, it would be
> perceived as (3,3,6).
>
>    With this information a red/green colour blind person could distinguish
> between (what a non-colour blind person would see as) grey and red in that
> grey (128,128,128) would map to (128,128,128) for a colour blind person,
> while red (255,0,0) would map to (128,128,0) for a colour blind person.
>
>    There also exist people who are completely colour blind, in that they
> can't distinguish between information sent from all three of their
> receptors. To simulate this, you could just average out all three
> channels; so as in the example earlier, (2,4,6) would map to (4,4,4),
> which is indeed a shade of grey for us. It might be misleading to call
> what they see "grey" though. If you use the HSL colour space (Hue
> Saturation Lightness) instead of RGB (Red Green Blue), basically these
> people can perceive Lightness normally, but have no Hue or Saturation
> information. To say that they see grey implies that they always see
> saturation as being zero.
>
>    As for traffic lights, I think if I were colour blind (either red/green
> or all 3), I'd mainly infer the colour of the light from the position of
> the light (in the vertical traffic lights, top is always red and bottom is
> always green; in the horizontal one, the outer ones are red, but I forget
> which is yellow and which is green - though in the horizontal ones they
> also use shapes, and round is green).
>
>    I also heard that most traffic lights now colour the "green" light as
> being blue-green. So a red/green colour blind person would be able to
> detect that the "green" light is one by the presence of blue, but perhaps
> wouldn't be able to differentiate between yellow and red.
>
>    - Oliver
>
>