HSI out of bounds values and hue shifting

[jtlapp]

The HSI conversion will take valid intensity values and convert them to RGB bytes > 255.

Also, shifting the intensity by a small amount can produce a rather large change in hue.

const cs = require('color-space');

console.log('HSI:');
let rgb1 = [ 0xb7, 0xc7, 0xff ];
let hsi = cs.rgb.hsi(rgb1);
let rgb2 = cs.hsi.rgb(hsi);
console.log(`     from RGB ${round(rgb1)} to HSI ${round(hsi)}`);
console.log(`  back to RGB ${round(rgb2)}`);
hsi[2] += 6;
let rgb3 = cs.hsi.rgb(hsi);
console.log(`  i+=6 to RGB ${round(rgb3)}`);

function round(vals) {
    return [Math.round(vals[0]), Math.round(vals[1]), Math.round(vals[2])];
}

Yields:

HSI:
     from RGB 183,199,255 to HSI 228,14,212
  back to RGB 183,199,255
  i+=6 to RGB 188,205,262

[jtlapp]

FYI @dfcreative

[dy]

Thanks for the catch! Can you help with fixing that?

[jtlapp]

There are so many ways to express this conversion, I'm not finding the algorithm you modeled. I'm coding it from scratch to see if I get better behavior. Will share when I'm done.

[jtlapp]

I implemented this algoirthm and got these results:

     from RGB 183,199,255 to HSI 227,14,212
  back to RGB 183,200,254
  i+=6 to RGB 188,206,261

Despite using two different algorithms, our results are in rough agreement. There must be something about HSI that I'm not understanding.

[dy]

I used this source http://web.archive.org/web/20130124054245/http://web2.clarkson.edu/class/image_process/RGB_to_HSI.pdf

[jtlapp]

I experimented with bounding the RGB outputs to 0..255 and the colors I get seem quite reasonable for my image transformations. I think that's all you need to do!