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iamstephenbrown/UIColor+Luminosity.swift

Last active January 24, 2022 21:37
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UIColor extension to adjust the luminosity of a colour
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UIColor+Luminosity.swift
import Foundation
import UIKit
// Fantastic explanation of how it works
// http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
fileprivate extension CGFloat {
/// clamp the supplied value between a min and max
/// - Parameter min: The min value
/// - Parameter max: The max value
func clamp(min: CGFloat, max: CGFloat) -> CGFloat {
if self < min {
return min
} else if self > max {
return max
} else {
return self
}
}
/// If colour value is less than 1, add 1 to it. If temp colour value is greater than 1, substract 1 from it
func convertToColourChannel() -> CGFloat {
let min: CGFloat = 0
let max: CGFloat = 1
let modifier: CGFloat = 1
if self < min {
return self + modifier
} else if self > max {
return self - max
} else {
return self
}
}
/// Formula to convert the calculated colour from colour multipliers
/// - Parameter temp1: Temp variable one (calculated from luminosity)
/// - Parameter temp2: Temp variable two (calcualted from temp1 and luminosity)
func convertToRGB(temp1: CGFloat, temp2: CGFloat) -> CGFloat {
if 6 * self < 1 {
return temp2 + (temp1 - temp2) * 6 * self
} else if 2 * self < 1 {
return temp1
} else if 3 * self < 2 {
return temp2 + (temp1 - temp2) * (0.666 - self) * 6
} else {
return temp2
}
}
}
extension UIColor {
/// Return a UIColor with adjusted luminosity, returns self if unable to convert
/// - Parameter newLuminosity: New luminosity, between 0 and 1 (percentage)
func withLuminosity(_ newLuminosity: CGFloat) -> UIColor {
// 1 - Convert the RGB values to the range 0-1
let coreColour = CIColor(color: self)
var red = coreColour.red
var green = coreColour.green
var blue = coreColour.blue
let alpha = coreColour.alpha
// 1a - Clamp these colours between 0 and 1 (combat sRGB colour space)
red = red.clamp(min: 0, max: 1)
green = green.clamp(min: 0, max: 1)
blue = blue.clamp(min: 0, max: 1)
// 2 - Find the minimum and maximum values of R, G and B.
guard let minRGB = [red, green, blue].min(), let maxRGB = [red, green, blue].max() else {
return self
}
// 3 - Now calculate the Luminace value by adding the max and min values and divide by 2.
var luminosity = (minRGB + maxRGB) / 2
// 4 - The next step is to find the Saturation.
// 4a - if min and max RGB are the same, we have 0 saturation
var saturation: CGFloat = 0
// 5 - Now we know that there is Saturation we need to do check the level of the Luminance in order to select the correct formula.
// If Luminance is smaller then 0.5, then Saturation = (max-min)/(max+min)
// If Luminance is bigger then 0.5. then Saturation = ( max-min)/(2.0-max-min)
if luminosity <= 0.5 {
saturation = (maxRGB - minRGB)/(maxRGB + minRGB)
} else if luminosity > 0.5 {
saturation = (maxRGB - minRGB)/(2.0 - maxRGB - minRGB)
} else {
// 0 if we are equal RGBs
}
// 6 - The Hue formula is depending on what RGB color channel is the max value. The three different formulas are:
var hue: CGFloat = 0
// 6a - If Red is max, then Hue = (G-B)/(max-min)
if red == maxRGB {
hue = (green - blue) / (maxRGB - minRGB)
}
// 6b - If Green is max, then Hue = 2.0 + (B-R)/(max-min)
else if green == maxRGB {
hue = 2.0 + ((blue - red) / (maxRGB - minRGB))
}
// 6c - If Blue is max, then Hue = 4.0 + (R-G)/(max-min)
else if blue == maxRGB {
hue = 4.0 + ((red - green) / (maxRGB - minRGB))
}
// 7 - The Hue value you get needs to be multiplied by 60 to convert it to degrees on the color circle
// If Hue becomes negative you need to add 360 to, because a circle has 360 degrees.
if hue < 0 {
hue += 360
} else {
hue = hue * 60
}
// we want to convert the luminosity. So we will.
luminosity = newLuminosity
// Now we need to convert back to RGB
// 1 - If there is no Saturation it means that it’s a shade of grey. So in that case we just need to convert the Luminance and set R,G and B to that level.
if saturation == 0 {
return UIColor(red: 1.0 * luminosity, green: 1.0 * luminosity, blue: 1.0 * luminosity, alpha: alpha)
}
// 2 - If Luminance is smaller then 0.5 (50%) then temporary_1 = Luminance x (1.0+Saturation)
// If Luminance is equal or larger then 0.5 (50%) then temporary_1 = Luminance + Saturation – Luminance x Saturation
var temporaryVariableOne: CGFloat = 0
if luminosity < 0.5 {
temporaryVariableOne = luminosity * (1 + saturation)
} else {
temporaryVariableOne = luminosity + saturation - luminosity * saturation
}
// 3 - Final calculated temporary variable
let temporaryVariableTwo = 2 * luminosity - temporaryVariableOne
// 4 - The next step is to convert the 360 degrees in a circle to 1 by dividing the angle by 360
let convertedHue = hue / 360
// 5 - Now we need a temporary variable for each colour channel
let tempRed = (convertedHue + 0.333).convertToColourChannel()
let tempGreen = convertedHue.convertToColourChannel()
let tempBlue = (convertedHue - 0.333).convertToColourChannel()
// 6 we must run up to 3 tests to select the correct formula for each colour channel, converting to RGB
let newRed = tempRed.convertToRGB(temp1: temporaryVariableOne, temp2: temporaryVariableTwo)
let newGreen = tempGreen.convertToRGB(temp1: temporaryVariableOne, temp2: temporaryVariableTwo)
let newBlue = tempBlue.convertToRGB(temp1: temporaryVariableOne, temp2: temporaryVariableTwo)
return UIColor(red: newRed, green: newGreen, blue: newBlue, alpha: alpha)
}
}
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