Why no Color.HSLToRGB?

Unity Engine
,
1

We have HSVToRGB, can we not have HSLToRGB?!
Maybe it is less used since HSV is often in color wheels, but the L value makes more sense in a way!
(personally I have trouble with HSV since you can not choose a color (hue/saturation) and then modify the light & dark to shade an object)

The code is freely available so throw it in!

2

Aren’t HSV and HSL just two different names for the same thing?

3

no

4

They are not the same, but almost. The only difference is how V or L is calculated. V is max(R,G,B) while L is (max(R,G,B) + min(R,G,B)) / 2. So L is the relative “lightness”. There are countless of different color spaces out there and Unity provides HSV conversion (note: not even from the very beginning. Can’t remember when they added the methods, though quite some time ago). Unity can not provide conversion from / to all potential color spaces. HSV is easier to calcuate, especially in reverse (HSV->RGB).

If you really need it, you can implement those conversions yourself. It’s not black magic, you know :slight_smile: The wikipedia article has some conversion logic you can look up. Or you simply search for a ready-to-use or easy-to-adapt solution

2 Likes
5

Unity 5.3 I think all the way back in 2015. I doubt that type has changed in all the years since. I’d be happy to mention it to some of the internal devs who work on low-hanging fruit but that’s no guarantee it’ll get added. All I can do though.

2 Likes
6

Thanks - I have code to do it, it is only a nice to have so I guess bigger priorities!!
But I am starting to question HSV’s heavy use - HSL means you can change from a light to dark version of a colour more easily than HSV (also called HSB perhaps as V/brightness is from black to full rgb of color)

7

Well almost - the ranges seem different like HSL 1,.5,1, HSV, 1,1,.5.
because at full hue brightness (L = 0.5 or V = 1) the saturation ends at mid-grey in HSL and white in HSV.
Is there a 1,1,1 version so you can combine both!!

8

I feel like anyone that needs it likely knows the necessary math to write the code for it.

GPT-4 HSL and HSI to RGB

using UnityEngine;

public static class ColorExtensions
{
    // Converts HSL to RGB.
    public static Color HSLToRGB(float h, float s, float l)
    {
        float r, g, b;
        if (s == 0)
        {
            r = g = b = l; // achromatic
        }
        else
        {
            var q = l < 0.5f ? l * (1 + s) : l + s - l * s;
            var p = 2 * l - q;
            r = HueToRGB(p, q, h + 1f / 3f);
            g = HueToRGB(p, q, h);
            b = HueToRGB(p, q, h - 1f / 3f);
        }

        return new Color(r, g, b);
    }

    // Helper method for HSLToRGB.
    private static float HueToRGB(float p, float q, float t)
    {
        if (t < 0f) t += 1f;
        if (t > 1f) t -= 1f;
        if (t < 1f / 6f) return p + (q - p) * 6f * t;
        if (t < 1f / 2f) return q;
        if (t < 2f / 3f) return p + (q - p) * (2f / 3f - t) * 6f;
        return p;
    }

    // Converts HSI to RGB.
    public static Color HSIToRGB(float h, float s, float i)
    {
        float r, g, b;

        if (h < 2f / 3f) // RGB Sector 1
        {
            b = i * (1 - s);
            r = i * (1 + s * Mathf.Cos(h * Mathf.PI * 2) / Mathf.Cos((1f / 3f - h) * Mathf.PI * 2));
            g = 3 * i - (r + b);
        }
        else if (h < 4f / 3f) // RGB Sector 2
        {
            h -= 2f / 3f;
            r = i * (1 - s);
            g = i * (1 + s * Mathf.Cos(h * Mathf.PI * 2) / Mathf.Cos((1f / 3f - h) * Mathf.PI * 2));
            b = 3 * i - (r + g);
        }
        else // RGB Sector 3
        {
            h -= 4f / 3f;
            g = i * (1 - s);
            b = i * (1 + s * Mathf.Cos(h * Mathf.PI * 2) / Mathf.Cos((1f / 3f - h) * Mathf.PI * 2));
            r = 3 * i - (g + b);
        }

        return new Color(r, g, b);
    }
}

If we’re going to request HSL to RGB we may as well request HSI to RGB too.