AForge.NET open source framework

// AForge Image Processing Library
//
// Copyright � Andrew Kirillov, 2005-2006
// andrew.kirillov@gmail.com
//
// Original idea from CxImage
// http://www.codeproject.com/bitmap/cximage.asp
//
namespace AForge.Imaging.Filters
{
	using System;
	using System.Drawing;
	using System.Drawing.Imaging;

	/// <summary>
	/// Dithering using Stevenson and Arce error diffusion
	/// </summary>
	public class StevensonArceDithering : ErrorDiffusionDithering
	{
		private static int[] coef1 = new int[] { 12, 26, 30, 16 };
//		private static int[] coef2 = new int[] { 5, 12, 12, 26, 12, 12, 5 };
		private static int[] coef2 = new int[] { 12, 26, 12 };
		private static int[] coef3 = new int[] { 5, 12, 12, 5 };

		/// <summary>
		/// Do error diffusion
		/// </summary>
		/// 
		/// <param name="error">Current error value</param>
		/// <param name="ptr">Pointer to current processing pixel</param>
		/// 
		/// <remarks>All parameters of the image and current processing pixel's coordinates
		/// are initialized by base class.</remarks>
		/// 
		protected override unsafe void Diffuse( int error, byte * ptr )
		{
			int ed;	// error diffusion

			// calculate error diffusion
			if ( x < widthM1 - 1 )
			{
				// right + 1 pixel
				ed = ptr[2] + ( error * 32 ) / 200;
				ed = ( ed < 0 ) ? 0 : ( ( ed > 255 ) ? 255 : ed );
				ptr[2] = (byte) ed;
			}

			if ( y < heightM1 )
			{
				// bottom pixels
				ptr += stride;
				for ( int i = -3, j = 0; i <= 3; i += 2, j++ )
				{
					if ( ( x + i >= 0 ) && ( x + i < width ) )
					{
						ed = ptr[i] + ( error * coef1[j] ) / 200;
						ed = ( ed < 0 ) ? 0 : ( ( ed > 255 ) ? 255 : ed );
						ptr[i] = (byte) ed;
					}
				}
			}

			if ( y < heightM1 - 1 )
			{
				// bottom + 1 pixels
				ptr += stride;
				for ( int i = -2, j = 0; i <= 2; i += 2, j++ )
				{
					if ( ( x + i >= 0 ) && ( x + i < width ) )
					{
						ed = ptr[i] + ( error * coef2[j] ) / 200;
						ed = ( ed < 0 ) ? 0 : ( ( ed > 255 ) ? 255 : ed );
						ptr[i] = (byte) ed;
					}
				}
			}

			if ( y < heightM1 - 2 )
			{
				// bottom + 2 pixels
				ptr += stride;
				for ( int i = -3, j = 0; i <= 3; i += 2, j++ )
				{
					if ( ( x + i >= 0 ) && ( x + i < width ) )
					{
						ed = ptr[i] + ( error * coef3[j] ) / 200;
						ed = ( ed < 0 ) ? 0 : ( ( ed > 255 ) ? 255 : ed );
						ptr[i] = (byte) ed;
					}
				}
			}
		}
	}
}