Respresention of spectrum

Respresention of spectrum

Post by Kwok Shu Ta » Fri, 29 Mar 1996 04:00:00



Hi,
        I would like to ask how to calculate the spectrum in order to
show the rainbow colour in viewing the diamond? And if I know the
wavelength range of the ray striking the diamond and also taking the xyz
coordinate, then transform the xyz -> rgb color space, then obtain the
rgb value to show the color, but it only shows the red and orange color,
and could not show the sparkling effect. Do I need the intensity value of
each wavelength or any other information?

Thanks a lot
--
Kwok Shu Tat, Philip (3?e1F)
BA Computing Studies Year 4
The Hong Kong Polytechnic University

 
 
 

Respresention of spectrum

Post by Victor Enge » Fri, 29 Mar 1996 04:00:00



>Hi,
>    I would like to ask how to calculate the spectrum in order to
>show the rainbow colour in viewing the diamond? And if I know the
>wavelength range of the ray striking the diamond and also taking the xyz
>coordinate, then transform the xyz -> rgb color space, then obtain the
>rgb value to show the color, but it only shows the red and orange color,
>and could not show the sparkling effect. Do I need the intensity value of
>each wavelength or any other information?

>Thanks a lot
>--
>Kwok Shu Tat, Philip (3?e1F)
>BA Computing Studies Year 4
>The Hong Kong Polytechnic University


Oh, this sounds like a fun project. I wish I were working on it. I'll
have to think about it for a while. Remember, though, that HSI or RGB or
probably whatever else method you are using are simply models and do not
reflect the way light actually works. This may affect your results. Let
me explain with a couple of examples. Take an example color from the
rainbow, say, orange. If you really choose the color from the rainbow,
you have a monochromatic color. This color is simulated with RGB by
adjusting the individual components of red, green, and blue until a
similar response by our cones is achieved as is achieved from the
monochromatic color. In other words, the pure orange color selected from
the rainbow LOOKS to us exactly the same as the combination of colors
red, green, blue of different intensities. However, as soon as you start
passing the light through something like a diamond, it will look
different, and this is not just on a computer. If you illuminate a
diamond with a monochromatic orange light, all glints, etc. on the
diamond will be in this same color. If you illuminate a diamond with a
combination of R,G,B that LOOKS like orange, the individual components
will separate, and you will see glints in different combinations of these
various components.

OK. What to do? I think you will have to ray trace a sampling of rays in
a range of frequencies. Then you will have to integrate the results and
convert back to RGB. This should get you what you want, but as you can
see it is very time consuming.

The reason all this is true is that different frequencies of light have
different coefficients of refraction. Perhaps a simple way to illustrate
what I'm talking about doing here is to take a simple prism and ray trace
it. As you know, a prism separates white light into a spectrum of the
component colors. If you shine a light composed of RGB FFFFFF colors,
what you really have is a combination of 3 frequencies of light. The
prism will separate these components, and the other side of the prism
will display as 3 rays of light, red, green, and blue, rather than an
entire spectrum.

I hope all this helped. I don't think I explained it very well, but I
hope you get the idea anyway.

 
 
 

1. Respresention of spectrum

Hi,
        I would like to ask how to calculate the spectrum in order to show the rainbow colour in
viewing the diamond? And if I know the wavelength range of the ray striking the diamond and also
taking the xyz coordinate, then transform the xyz -> rgb color space, then obtain the rgb value
to show the color, but it only shows the red and orange color, and could not show the sparkling
effect. Do I need the intensity value of each wavelength or any other information?

Thanks a lot
--
Kwok Shu Tat, Philip (3?e1F)
BA Computing Studies Year 4
The Hong Kong Polytechnic University

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