Converting from RGB to HSL with Objective C
I'm quite new to objective c but have been programming for a while. I started creating a function that would convert from RGB to HSL and back aga开发者_运维问答in but I get a feeling it is way too long and headed in the wrong direction. Does anyone know of a simple way to perform this conversion?
NSColor is missing in iPhone SDK. You can use this utility to convert from RGB to HSL space and back:
https://github.com/alessani/ColorConverter
You can use NSColor
, I think.
CGFloat r, g, b, a, h, s, b, a2;
NSColor *c = [NSColor colorWithCalibratedRed:r green:g blue:b alpha:a];
[c getHue:&h saturation:&s brightness:&b alpha:&a2];
On second thought, I don't know if NSColor
is available in the iPhone frameworks or not - isn't there a UIColor
? Anyway I'll leave this answer in case someone searching for an OS X solution ends up here.
Here's what I'm using:
static void RVNColorRGBtoHSL(CGFloat red, CGFloat green, CGFloat blue, CGFloat *hue, CGFloat *saturation, CGFloat *lightness)
{
CGFloat r = red / 255.0f;
CGFloat g = green / 255.0f;
CGFloat b = blue / 255.0f;
CGFloat max = MAX(r, g);
max = MAX(max, b);
CGFloat min = MIN(r, g);
min = MIN(min, b);
CGFloat h;
CGFloat s;
CGFloat l = (max + min) / 2.0f;
if (max == min) {
h = 0.0f;
s = 0.0f;
}
else {
CGFloat d = max - min;
s = l > 0.5f ? d / (2.0f - max - min) : d / (max + min);
if (max == r) {
h = (g - b) / d + (g < b ? 6.0f : 0.0f);
}
else if (max == g) {
h = (b - r) / d + 2.0f;
}
else if (max == b) {
h = (r - g) / d + 4.0f;
}
h /= 6.0f;
}
if (hue) {
*hue = roundf(h * 255.0f);
}
if (saturation) {
*saturation = roundf(s * 255.0f);
}
if (lightness) {
*lightness = roundf(l * 255.0f);
}
}
And here's how to call it:
CGFloat h, s, l;
RVNColorRGBtoHSL(r, g, b,
&h, &s, &l);
You can add the UIColor-HSVAdditions.h/.m category to your app to add a set of operations to UIColor for working with hue, saturation and value. See http://bravobug.com/news/?p=448 and this ArsTechnica article also.
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