CODEWITHSUNDEEP
javargbhuehsl
Jaron
Jaron

Reputation: 13

Incorrect rgb to hue convertion

I'm trying to convert a rgb color to hsl in Java, i have searched for many codes that explain how you convert rgb to hsl, i now have saturation and lightness working, but the hue value is incorrect

I am now trying to convert rgb to hsl and then back.

the rgb values i am using are

red: 54 green: 43 blue: 21

The hsl values i get are

hue: 260 saturation: 44 lightness: 15

I tried to convert the rgb values to hsl at https://www.rapidtables.com/convert/color/rgb-to-hsl.html

The values i get there are

hue: 40 saturation: 44.0 lightness: 14.7

Does anyone know what i'm doing wrong in converting rgb to hsl? Here is my code

public static Map<String, Integer> rgbToHsl(Integer red, Integer green, Integer blue){
        Float redDouble = ((float)red) / 255.0f;
        Float greenDouble = ((float)green) / 255.0f;
        Float blueDouble = ((float)blue) / 255.0f;

        Float max = Math.max(Math.max(redDouble, greenDouble), blueDouble);
        Float min = Math.min(Math.min(redDouble, greenDouble), blueDouble);

        Float chroma = max - min;
        Float hue = chroma == 0.0f ? 0.0f : 
            (max == redDouble ? (greenDouble - blueDouble) / chroma : 
            (max == greenDouble ? 2f + (blueDouble - redDouble) / chroma : 
            4f + (redDouble - greenDouble) / chroma));

        Float lightness = (max + min) * 0.5f;
        Float saturation = chroma == 0.0f ? 0.0f : (lightness > 0.5f ? chroma / (2.0f - max - min) : chroma / (max + min));

        return Map.ofEntries(
            Map.entry("hue", (int) Math.round(hue * 60)),
            Map.entry("saturation", (int) Math.round(saturation * 100)),
            Map.entry("lightness", (int) Math.round(lightness * 100))
        );
    }

Upvotes: 1

Views: 141

Answers (2)

Andrey Tyukin
Andrey Tyukin

Reputation: 44992

When you use boxed Floats everywhere, the Math.max(Math.max(a, b), c) will unbox the arguments a, b and c, then perform the computation, then box them back into a Float.

The result will be a new object, unequal to all three a, b and c.

Therefore, the identity comparisons max == redDouble and max == greenDouble will always be false.

Eliminate the boxed types, use floats everywhere, it's both faster and clearer.

Even better: never use either == or equals on any kind of floating-point values. See, for example, how here additional boolean flags were used. Booleans are not susceptible to tiny rounding errors.

Upvotes: 0

sunrise
sunrise

Reputation: 404

For the hue value if red is the maximum, you forgot to convert it by modulus 6.

According to what IntelliJ is showing me, it doesn't believe max == redDouble even though their printed values look identical. So, your nested logic for the hue is calculating the wrong part. I would suggest you write some logic to figure out whether you're looking for white, red, green or blue as a string, then use a switch block with the new colour string as your trigger to decide which value to return. This will be longer, but probably more readable as well. Although I am a fan of the ternary operator, nesting them can be muddling.

Upvotes: 0

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