Map rainbow colors to RGB

Question

Suppose I have a class RainbowColorsMapper with the constructor RainbowColorsMapper(int n), where n>=2. Now I want to have continuous mapping of rainbow colors from red to violet which I get using the method mapper.getColor(int number) where low values correspond to red end, and high near n to violet end. If n = 2, mapper.getColor(0) returns most left color of the spectrum (near red), and mapper.getColor(1) returns the most right color. Same with bigger n with automatic scaling.

My question: can this be done relatively easy, and if yes what are suggestions on the algorithm?

Er: "RainbowColorsMapper(int n), where n>=2" and "mapper.getColor(1) returns the most right color"? What are you talking about, Willis? — Tom Anderson, Apr 01 '11 at 13:04

score 8 · Accepted Answer · answered Apr 01 '11 at 13:10

8

The easiest way to do this will be to work in the HSL colourspace rather than RGB. Create colours where the saturation and lightness are fixed (to 100% and 50%, i would suggest), and the hue varies between suitable endpoints (which you might need to experiment to find). Convert the HSL values to RGB using Color.getHSBColor.

answered Apr 01 '11 at 13:10

Tom Anderson

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Yes, seems the easiest way. Thanks for pointing in the right direction. – bvk256 Apr 01 '11 at 13:19

score 2 · Answer 2 · edited May 23 '17 at 11:58

2

Remember that the colours of the rainbow are ordered according to wavelength, so basically in your model, n is somehow related to wavelength. So your question essentially boils down to mapping wavelength (n) to RGB. This is not an entirely trivial process, but for a start, you could check this question out:

Convert light frequency to RGB?

edited May 23 '17 at 11:58

Community

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answered Apr 01 '11 at 13:06

Matt Dunn

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This would be the best option if mapping wavelengths wouldn't be so problematic. – bvk256 Apr 01 '11 at 13:25

score 0 · Answer 3 · answered Apr 01 '11 at 13:02

0

Or use a Hue Saturation Value color model, and iterate over Hue.

answered Apr 01 '11 at 13:02

Mikeb

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score 0 · Answer 4 · answered Apr 01 '11 at 13:06

0

You basically have a hue change from 0 to 300 in the colour model

How to calculate RGB from Hue you can find on Wikipedia

answered Apr 01 '11 at 13:06

Fabian Tschachtli

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score 0 · Answer 5 · answered Apr 01 '11 at 15:41

0

HSL Color allows you to do this easily.

answered Apr 01 '11 at 15:41

camickr

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score -1 · Answer 6 · edited Dec 31 '19 at 06:03

 private int r = 255;
 private int g = 0;
 private int b = 0;

 private void nextRGB() {
     if (r == 255 && g < 255 && b == 0) {
         g++;
     }
     if (g == 255 && r > 0 && b == 0) {
         r--;
     }
     if (g == 255 && b < 255 && r == 0) {
         b++;
     }
     if (b == 255 && g > 0 && r == 0) {
         g--;
     }
     if (b == 255 && r < 255 && g == 0) {
         r++;
     }
     if (r == 255 && b > 0 && g == 0) {
         b--;
     }
 }

 public Color nextColor() {
     nextRGB();
     return makeColor();
 }

 private Color makeColor() {
     return new Color(r, g, b);
 }

I might be wrong, but that way there are always two fixed values, so there will be no mid-tones, right? I mean `5,230,123`for example isn't possible... — Jochen Birkle, Apr 03 '14 at 15:41

Map rainbow colors to RGB

6 Answers6

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