Mean Removal

This algorithm is like Sharpen filter. Unlike the Sharpen filter, which only worked in the horizontal and vertical directions, this one spreads it's influence diagonally as well, with the following result on the same source image.

   

• C#
• VB.Net

									class ConvolutionMatrix
{
	public ConvolutionMatrix()
	{
		Pixel = 1;
		Factor = 1;
	}

	public void Apply(int Val)
	{
		TopLeft = TopMid = TopRight = MidLeft = MidRight = BottomLeft = BottomMid = BottomRight = Pixel = Val;
	}

	public int TopLeft { get; set; }

	public int TopMid { get; set; }

	public int TopRight { get; set; }

	public int MidLeft { get; set; }

	public int MidRight { get; set; }

	public int BottomLeft { get; set; }

	public int BottomMid { get; set; }

	public int BottomRight { get; set; }

	public int Pixel { get; set; }

	public int Factor { get; set; }

	public int Offset { get; set; }
}

class Convolution
{
	public void Convolution3x3(ref Bitmap bmp)
	{
		int Factor = Matrix.Factor;

		if (Factor == 0) return;

		int TopLeft = Matrix.TopLeft;
		int TopMid = Matrix.TopMid;
		int TopRight = Matrix.TopRight;
		int MidLeft = Matrix.MidLeft;
		int MidRight = Matrix.MidRight;
		int BottomLeft = Matrix.BottomLeft;
		int BottomMid = Matrix.BottomMid;
		int BottomRight = Matrix.BottomRight;
		int Pixel = Matrix.Pixel;
		int Offset = Matrix.Offset;

		Bitmap TempBmp = (Bitmap)bmp.Clone();

		BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
		BitmapData TempBmpData = TempBmp.LockBits(new Rectangle(0, 0, TempBmp.Width, TempBmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

		unsafe
		{
			byte* ptr = (byte*)bmpData.Scan0.ToPointer();
			byte* TempPtr = (byte*)TempBmpData.Scan0.ToPointer();

			int Pix = 0;
			int Stride = bmpData.Stride;
			int DoubleStride = Stride * 2;
			int Width = bmp.Width - 2;
			int Height = bmp.Height - 2;
			int stopAddress = (int)ptr + bmpData.Stride * bmpData.Height;

			for (int y = 0; y < Height; ++y)
				for (int x = 0; x < Width; ++x)
				{
					Pix = (((((TempPtr[2] * TopLeft) + (TempPtr[5] * TopMid) + (TempPtr[8] * TopRight)) +
					  ((TempPtr[2 + Stride] * MidLeft) + (TempPtr[5 + Stride] * Pixel) + (TempPtr[8 + Stride] * MidRight)) +
					  ((TempPtr[2 + DoubleStride] * BottomLeft) + (TempPtr[5 + DoubleStride] * BottomMid) + (TempPtr[8 + DoubleStride] * BottomRight))) / Factor) + Offset);

					if (Pix < 0) Pix = 0;
					else if (Pix > 255) Pix = 255;

					ptr[5 + Stride] = (byte)Pix;

					Pix = (((((TempPtr[1] * TopLeft) + (TempPtr[4] * TopMid) + (TempPtr[7] * TopRight)) +
						  ((TempPtr[1 + Stride] * MidLeft) + (TempPtr[4 + Stride] * Pixel) + (TempPtr[7 + Stride] * MidRight)) +
						  ((TempPtr[1 + DoubleStride] * BottomLeft) + (TempPtr[4 + DoubleStride] * BottomMid) + (TempPtr[7 + DoubleStride] * BottomRight))) / Factor) + Offset);

					if (Pix < 0) Pix = 0;
					else if (Pix > 255) Pix = 255;

					ptr[4 + Stride] = (byte)Pix;

					Pix = (((((TempPtr[0] * TopLeft) + (TempPtr[3] * TopMid) + (TempPtr[6] * TopRight)) +
						  ((TempPtr[0 + Stride] * MidLeft) + (TempPtr[3 + Stride] * Pixel) + (TempPtr[6 + Stride] * MidRight)) +
						  ((TempPtr[0 + DoubleStride] * BottomLeft) + (TempPtr[3 + DoubleStride] * BottomMid) + (TempPtr[6 + DoubleStride] * BottomRight))) / Factor) + Offset);

					if (Pix < 0) Pix = 0;
					else if (Pix > 255) Pix = 255;

					ptr[3 + Stride] = (byte)Pix;

					ptr += 3;
					TempPtr += 3;
				}
		}

		bmp.UnlockBits(bmpData);
		TempBmp.UnlockBits(TempBmpData);
	}

	public ConvolutionMatrix Matrix { get; set; }
}

public static void ApplyMeanRemoval(ref Bitmap bmp, int weight)
{
	ConvolutionMatrix m = new ConvolutionMatrix();
	m.Apply(-1);
	m.Pixel = weight;
	m.Factor = weight - 8;

	Convolution C = new Convolution();
	C.Matrix = m;
	C.Convolution3x3(ref bmp);
}
								

Example

									Bitmap b = (Bitmap)Image.FromFile("rose.jpg");
ApplyMeanRemoval(ref b, 9);