I am trying to create a wallpaper and am using the HSV conversion in the "android.graphics.color" class. I was very surprised when i realized that a conversion of a created HSV color with a specified hue (0..360) to a rgb color (an integer) and a back conversion to a HSV color will not result in the same hue. This is my code:
int c = Color.HSVToColor(new float[] { 100f, 1, 1 });
float[] f = new float[3];
Color.colorToHSV(c, f);
alert(f[0]);
I am starting with a hue of 100 degree and the result is 99.76471. I wonder why there is that (in my opinion) relatively big inaccuracy.
But a much bigger problem is, that when you put that value in the code again, the new result decreases again.
int c = Color.HSVToColor(new float[] { 99.76471f, 1, 1 });
float[] f = new float[3];
Color.colorToHSV(c, f);
alert(f[0]);
If I start with 99.76471, I get 99.52941. This is kind of a problem for me. I did something similar in java with the "java.awt.Color" class where I did not have those problems. Unfortunately, I cannot use this class in android.
This is an interesting problem. It's not avoidable with the android class because of low float precision. However, I found a similar solution written in javascript here.
If it's important enough for you to want to define your own method/class to do the conversions, here is a Java conversion which should give you better precision:
@Size(3)
/** Does the same as {@link android.graphics.Color#colorToHSV(int, float[])} */
public double[] colorToHSV(@ColorInt int color) {
//this line copied vertabim
return rgbToHsv((color >> 16) & 0xFF, (color >> 8) & 0xFF, color & 0xFF);
}
@Size(3)
public double[] rgbToHsv(double r, double g, double b) {
final double max = Math.max(r, Math.max(g, b));
final double min = Math.min(r, Math.min(g, b));
final double diff = max - min;
final double h;
final double s = ((max == 0d)? 0d : diff / max);
final double v = max / 255d;
if (min == max) {
h = 0d;
} else if (r == max) {
double tempH = (g - b) + diff * (g < b ? 6: 0);
tempH /= 6 * diff;
h = tempH;
} else if (g == max) {
double tempH = (b - r) + diff * 2;
tempH /= 6 * diff;
h = tempH;
} else {
double tempH = (r - g) + diff * 4;
tempH /= 6 * diff;
h = tempH;
}
return new double[] { h, s, v };
}
I have to confess ignorance here - I've done quick conversion and not had time to test properly. There might be a more optimal solution, but this should get you started at least.
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