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Image Processing for Dummies with C# and GDI+ Part 6 - The HSL color space

, 28 Jun 2004
A discussion of the HSL color space, including code for a color picker and image filters
using System;
using System.Drawing;
using System.Drawing.Imaging;

namespace CSharpFilters
{
	public class YUV
	{
		public byte Y;
		public byte U;
		public byte V;

		public YUV(byte Y, byte U, byte V)
		{
			this.Y = Y;
			this.U = U;
			this.V = V;
		}

		public static YUV FromRGB(Color c)
		{
			byte Y, U, V;

			Y = (byte)(((  66 * c.R + 129 * c.G +  25 * c.B + 128) >> 8) +  16);
			U = (byte)((( -38 * c.R -  74 * c.G + 112 * c.B + 128) >> 8) + 128);
			V = (byte)((( 112 * c.R -  94 * c.G -  18 * c.B + 128) >> 8) + 128);
			
			return new YUV(Y,U,V);
		}

		public Color RGB
		{
			get
			{
				int C = Y - 16;
				int D = U - 128;
				int E = V - 128;

				byte R, G, B;

				R = (byte)Math.Max(Math.Min((( 298 * C           + 409 * E + 128) >> 8), 255), 0);
				G = (byte)Math.Max(Math.Min((( 298 * C - 100 * D - 208 * E + 128) >> 8), 255), 0);
				B = (byte)Math.Max(Math.Min((( 298 * C + 516 * D           + 128) >> 8), 255), 0);

				return Color.FromArgb(R,G,B);
			}
		}
	}

	public class HSL
	{
		private float h;
		private float s;
		private float l;

		public float Hue
		{
			get
			{
				return h;
			}
			set
			{
				h = (float)(Math.Abs(value)%360);
			}
		}

		public float Saturation
		{
			get
			{
				return s;
			}
			set
			{
				s = (float)Math.Max(Math.Min(1.0, value), 0.0);
			}
		}

		public float Luminance
		{
			get
			{
				return l;
			}
			set
			{
				l = (float)Math.Max(Math.Min(1.0, value), 0.0);
			}
		}

		private HSL()
		{
		}
		public HSL(float hue, float saturation, float luminance)
		{
			Hue = hue;
			Saturation = saturation;
			Luminance = luminance;
		}


		public Color RGB
		{
			get
			{
				double r=0,g=0,b=0; 

				double temp1,temp2; 

				double normalisedH = h/360.0;

  				if(l==0) 
				{ 
					r=g=b=0; 
				} 
				else 
				{ 
					if(s==0) 
					{ 
						r=g=b=l; 
					} 
					else 
					{ 
						temp2 = ((l<=0.5) ? l*(1.0+s) : l+s-(l*s)); 

						temp1 = 2.0*l-temp2; 

             			double[] t3=new double[]{normalisedH+1.0/3.0,normalisedH,normalisedH-1.0/3.0}; 

						double[] clr=new double[]{0,0,0}; 

						for(int i=0;i<3;++i) 
						{ 
							if(t3[i]<0) 
								t3[i]+=1.0; 

							if(t3[i]>1) 
								t3[i]-=1.0; 

							if(6.0*t3[i] < 1.0) 
								clr[i]=temp1+(temp2-temp1)*t3[i]*6.0; 
							else if(2.0*t3[i] < 1.0) 
								clr[i]=temp2; 
							else if(3.0*t3[i] < 2.0) 
								clr[i]=(temp1+(temp2-temp1)*((2.0/3.0)-t3[i])*6.0); 
							else 
								clr[i]=temp1; 

						} 

						r=clr[0]; 
						g=clr[1]; 
						b=clr[2]; 
					} 

				} 
  				return Color.FromArgb((int)(255*r),(int)(255*g),(int)(255*b)); 
			}
		}

		private static byte toRGB(float rm1, float rm2, float rh)
		{
			if(rh>360) rh-=360;
			else if(rh<  0) rh+=360;

			if(rh< 60) rm1=rm1+(rm2-rm1)*rh/60;   
			else if(rh<180) rm1=rm2;
			else if(rh<240) rm1=rm1+(rm2-rm1)*(240-rh)/60;      

			return (byte)(rm1*255);
		}


		public static HSL FromRGB(byte red, byte green, byte blue)
		{
			return FromRGB(Color.FromArgb(red, green, blue));
		}

		public static HSL FromRGB(Color c)
		{
			return new HSL(c.GetHue(), c.GetSaturation(), c.GetBrightness());
		}
	}

	/// <summary>
	/// Summary description for ColorSpace.
	/// </summary>
	public class ColorSpace
	{
		public ColorSpace()
		{
		}

		public static Bitmap Luminance(Bitmap source, float factor)
		{
			int width = source.Width;
			int height = source.Height;

			Rectangle rc = new Rectangle(0, 0, width, height);

			if (source.PixelFormat != PixelFormat.Format24bppRgb) source = source.Clone(rc, PixelFormat.Format24bppRgb);

			Bitmap dest = new Bitmap(width, height, source.PixelFormat);

			BitmapData dataSrc = source.LockBits(rc, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
			BitmapData dataDest = dest.LockBits(rc, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

			int offset = dataSrc.Stride - (width*3);

			unsafe
			{
				byte * bytesSrc = (byte *)(void *)dataSrc.Scan0;
				byte * bytesDest = (byte *)(void *)dataDest.Scan0;

				for (int y = 0; y < height; ++y)
				{
					for (int x = 0; x < width; ++x)
					{
						HSL hsl = HSL.FromRGB(bytesSrc[2], bytesSrc[1], bytesSrc[0]); // Still BGR
						hsl.Luminance *= factor;

						Color c = hsl.RGB;

						bytesDest[0] = c.B;
						bytesDest[1] = c.G;
						bytesDest[2] = c.R;

						bytesSrc += 3;
						bytesDest += 3;
					}

					bytesDest += offset;
					bytesSrc += offset;
				}

				source.UnlockBits(dataSrc);
				dest.UnlockBits(dataDest);
			}
	
			return dest;
		}

		public static Bitmap Hue(Bitmap source, float factor)
		{
			int width = source.Width;
			int height = source.Height;

			Rectangle rc = new Rectangle(0, 0, width, height);

			if (source.PixelFormat != PixelFormat.Format24bppRgb) source = source.Clone(rc, PixelFormat.Format24bppRgb);

			Bitmap dest = new Bitmap(width, height, source.PixelFormat);

			BitmapData dataSrc = source.LockBits(rc, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
			BitmapData dataDest = dest.LockBits(rc, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

			int offset = dataSrc.Stride - (width*3);

			unsafe
			{
				byte * bytesSrc = (byte *)(void *)dataSrc.Scan0;
				byte * bytesDest = (byte *)(void *)dataDest.Scan0;

				for (int y = 0; y < height; ++y)
				{
					for (int x = 0; x < width; ++x)
					{
						HSL hsl = HSL.FromRGB(bytesSrc[2], bytesSrc[1], bytesSrc[0]); // Still BGR
						hsl.Hue *= factor;

						Color c = hsl.RGB;

						bytesDest[0] = c.B;
						bytesDest[1] = c.G;
						bytesDest[2] = c.R;

						bytesSrc += 3;
						bytesDest += 3;
					}

					bytesDest += offset;
					bytesSrc += offset;
				}

				source.UnlockBits(dataSrc);
				dest.UnlockBits(dataDest);
			}
	
			return dest;
		}

		public static Bitmap Saturation(Bitmap source, float factor)
		{
			int width = source.Width;
			int height = source.Height;

			Rectangle rc = new Rectangle(0, 0, width, height);

			if (source.PixelFormat != PixelFormat.Format24bppRgb) source = source.Clone(rc, PixelFormat.Format24bppRgb);

			Bitmap dest = new Bitmap(width, height, source.PixelFormat);

			BitmapData dataSrc = source.LockBits(rc, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
			BitmapData dataDest = dest.LockBits(rc, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

			int offset = dataSrc.Stride - (width*3);

			unsafe
			{
				byte * bytesSrc = (byte *)(void *)dataSrc.Scan0;
				byte * bytesDest = (byte *)(void *)dataDest.Scan0;

				for (int y = 0; y < height; ++y)
				{
					for (int x = 0; x < width; ++x)
					{
						HSL hsl = HSL.FromRGB(bytesSrc[2], bytesSrc[1], bytesSrc[0]); // Still BGR
						hsl.Saturation *= factor;

						Color c = hsl.RGB;

						bytesDest[0] = c.B;
						bytesDest[1] = c.G;
						bytesDest[2] = c.R;

						bytesSrc += 3;
						bytesDest += 3;
					}

					bytesDest += offset;
					bytesSrc += offset;
				}

				source.UnlockBits(dataSrc);
				dest.UnlockBits(dataDest);
			}
	
			return dest;
		}
	}
}

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About the Author

Christian Graus
Software Developer (Senior)
Australia Australia
Programming computers ( self taught ) since about 1984 when I bought my first Apple ][. Was working on a GUI library to interface Win32 to Python, and writing graphics filters in my spare time, and then building n-tiered apps using asp, atl and asp.net in my job at Dytech. After 4 years there, I've started working from home, at first for Code Project and now for a vet telemedicine company. I owned part of a company that sells client education software in the vet market, but we sold that and I worked for the owners for five years before leaving to get away from the travel, and spend more time with my family. I now work for a company here in Hobart, doing all sorts of Microsoft based stuff in C++ and C#, with a lot of T-SQL in the mix.

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