# Thread: Help! I'm Colour Blind.

1. ## Re: Help! I'm Colour Blind.

Originally Posted by Del_CtrlnoAlt
crap leh... if i got color blind... then i should see both screen having the exact same color rite... how come i see a difference between them?
cos ur too quick to judge ? think it through. colour deficency means u are less sensitive to certain colours in a particular space .. e.g green / red .. (unless u're the type that can't see any colours at all).

Using a mathematical formula, the website SIMULATES the colour deficiency by changing the values of colours. So it only stands to reason what what you see is also a modified perception, since the colour values between the actual image and the simulated image change for you as well. (for example, if a normal person sees a colour #FF7700, the image generated by this site is (to simulate colour deficiency) #FF4400 ... obviously, when u see the original image, you would see #FF4400 and the modified colour as #FF1100)

2. ## Re: Help! I'm Colour Blind.

Originally Posted by Del_CtrlnoAlt
sometimes i do wonder... you ask me a question but it seems so hard to understand... can make it in simple english?
Sorry for the slow reply and my English (it isn't my first language). I've read up a bit on colour blindness (not the least through the links provided by darrelchia), which answered my question. Anyway, I thought I'd share with you.

Preliminary: Metamerism.

The physical origin of "colour" is the spectral distribution of light energy - in other words, how much intensity is there for each wavelength. There are, of course, an infinite number of wavelengths.

The "normal" human eye has however only 3 types of receptors used in colour vision, each with a different sensitivity curve with respect to wavelengths. As a consequence, the perception of colour is based on only 3 "weighted intensities" - one per receptor type. This triple is also called "tristimulus" in the literature.

It is obvious that there must be an infinite number of spectra that will result in the same tristimulus, i.e. the same perceived colour. This is known as metamerism and the basis for photograpahic/print processes using a small number of inks/dyes as "primary colours".

My question:

If I have two spectral distributions (e.g. a natural scene and it's colour photo) which result in the same tristimulus (and thus colour perception) for a "normal sighted" person, would they also look indistinguishable to a colour blind person?

There are different types of colour blindness/colour vision anomalies. In cases where one or more "normal" receptor types are simply missing, a "correct colour" photo would also look "correct" to the colour blind person.

However, there are also mutations that change the spectral response of the colour receptors. In such a case, "identical colours" would look different to the affected person.

Even more interesting, by combining "normal" with "anormal" genes, there appears a small chance of tetrachromats and possibly pentachromats - i.e. people whose vision is not based on 3, but 4 or more "primary colours". Such persons would have better colour vision than "normal", to the point that standard colour photography and printing processes simply would not work anymore because they're based on the assumption of 3 primary colours.

I hope that is clear enough... if not, maybe a native speaker can help explain it in simpler terms?

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