Hex <=> Hsv mutual conversion not equal

[noyobo]

Thank you for your the colr 😃

I found some colors can not be equal when converted;

test.js

'use strict';

var assert = require('assert');
var Colr = require('../index');

var colr = new Colr();

describe('clor hsv', function() {
  // #81468f
  it('from hex #81468f should to hsv [289, 51, 56]', function(done) {
    var hsv = colr.fromHex('#81468f').toHsvArray();
    assert.deepEqual(hsv, [289, 51, 56]);
    done();
  });

  it('from hsv [289, 51, 56] should to hex #81468f', function(done) {
    var hex = colr.fromHsvArray([289, 51, 56]).toHex();
    assert.equal(hex, '#81468f');
    done();
  });

  it('from hsv [288, 51, 56] should to hex #80468f', function(done) {
    var hex = colr.fromHsvArray([288, 51, 56]).toHex();
    assert.equal(hex, '#80468f');
    done();
  });

  it('from hex #80468f should to hsv [288, 51, 56]', function(done) {
    var hsv = colr.fromHex('#80468f').toHsvArray();
    assert.deepEqual(hsv, [289, 51, 56]);
    done();
  });
});

result:

  clor hsv
    ✓ from hex #81468f should to hsv [289, 51, 56]
    1) from hsv [289, 51, 56] should to hex #81468f
    ✓ from hsv [288, 51, 56] should to hex #80468f
    2) from hex #80468f should to hsv [288, 51, 56]


  2 passing (23ms)
  2 failing

[stayradiated]

There seems to be a mistake in the last test:

it('from hex #80468f should to hsv [288, 51, 56]', function(done) {
    ...
    assert.deepEqual(hsv, [289, 51, 56]);
    ...
});

After fixing that, the results I get when I run the test are:

  clor hsv
    1) from hex #81468f should to hsv [289, 51, 56]
    ✓ from hsv [289, 51, 56] should to hex #81468f
    ✓ from hsv [288, 51, 56] should to hex #80468f
    ✓ from hex #80468f should to hsv [288, 51, 56]

  3 passing (18ms)
  1 failing

I then checked in Photoshop, using the color picker:

// hex to hsv
#80468f -> hsv(288, 51, 56)
#81468f -> hsv(288, 51, 56)

// hsv to hex
hsv(288, 51, 56) -> #80468f
hsv(289, 51, 56) -> #81468f

I think this is just a rounding error due to not enough significant figures.

If you need accurate results, try using:

• .toRawHsvArray() instead of .toHsvArray()
• .toRawRgbArray() instead of .toHex()

Conversions

// hex to rgb to raw hsv to rounded hsv
#80468f -> rgb(128, 70, 143) -> hsv(287.67, 51.05, 56.08) -> hsv(288, 51, 56)
#81468f -> rgb(129, 70, 143) -> hsv(288.49, 51.05, 56.08) -> hsv(288, 51, 56)

// rounded hsv to raw rgb to rounded rgb to hex
hsv(288, 51, 56) -> rgb(128.23, 69.97, 142.8) -> rgb(128, 70, 143) -> #80468f 
hsv(289, 51, 56) -> rgb(129.45, 69.97, 142.8) -> rgb(129, 70, 143) -> #81468f

// raw rgb to raw hsv
rgb(128.23, 69.97, 142.8) -> hsv(288, 51, 56)
rgb(129.45, 69.97, 142.8) -> hsv(289, 51, 56)

// raw hsv to raw rgb
hsv(287.67, 51.05, 56.08) -> rgb(128, 70, 143)
hsv(288.49, 51.05, 56.08) -> rgb(129, 70, 143)

Extended Tests

'use strict';

var assert = require('assert');
var Colr = require('./index');

var colr = new Colr();

describe('colr hsv', function() {

  // rgb[128, 70, 143] = #80468f
  // rgb[129, 70, 143] = #81468f

  it('from rgb [128, 70, 143] to hsv [288, 51, 56]', function(done) {
    var c = colr.fromRgbArray([128, 70, 143]);
    assert.deepEqual(c.toRawHsvArray(), [
      287.6712328767123,
      51.048951048951054,
      56.07843137254902,
    ]);
    assert.deepEqual(c.toHsvArray(), [
      288,
      51,
      56,
    ]);
    done();
  });

  it('from rgb [129, 70, 143] to hsv [288, 51, 56]', function(done) {
    var c = colr.fromRgbArray([129, 70, 143]);
    assert.deepEqual(c.toRawHsvArray(), [
      288.4931506849315,
      51.048951048951054,
      56.07843137254902,
    ]);
    assert.deepEqual(c.toHsvArray(), [
      288,
      51,
      56,
    ]);
    done();
  });

  it('from hsv [288, 51, 56] to rgb [128, 70, 143]', function(done) {
    var c = colr.fromHsvArray([288, 51, 56]);
    assert.deepEqual(c.toRawRgbArray(), [
      128.2344,
      69.97200000000001,
      142.8,
    ]);
    assert.deepEqual(c.toRgbArray(), [
      128,
      70,
      143,
    ]);
    done();
  });

  it('from hsv [289, 51, 56] to rgb [129, 70, 143]', function(done) {
    var c = colr.fromHsvArray([289, 51, 56]);
    assert.deepEqual(c.toRawRgbArray(), [
      129.44819999999999,
      69.97200000000001,
      142.8,
    ]);
    assert.deepEqual(c.toRgbArray(), [
      129,
      70,
      143,
    ]);
    done();
  });
});

Test Results

  colr hsv
    ✓ from rgb [128, 70, 143] to hsv [288, 51, 56]
    ✓ from rgb [129, 70, 143] to hsv [288, 51, 56]
    ✓ from hsv [288, 51, 56] to rgb [128, 70, 143]
    ✓ from hsv [289, 51, 56] to rgb [129, 70, 143]

[noyobo]

Sorry for mistake in the last test 😧

Thank you for your answer, This seems a reasonable a rounding value.