Contrast

This algorithm adjusts the contrast of specified image in RGB color space. This algorithm works by increasing RGB values of bright pixels and decreasing RGB values of dark pixels.

   

• C#
• VB.Net

									public static void ApplyContrast(ref Bitmap bmp, sbyte contrastValue)
{
	if (contrastValue < -100 || contrastValue > 100) return;

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

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

		int stopAddress = (int)ptr + bmpData.Stride * bmpData.Height;

		double pixel = 0, contrast = (100.0 + contrastValue) / 100.0;

		contrast *= contrast;

		while ((int)ptr != stopAddress)
		{
			pixel = ptr[0] / 255.0;
			pixel -= 0.5;
			pixel *= contrast;
			pixel += 0.5;
			pixel *= 255;
			if (pixel < 0) pixel = 0;
			else if (pixel > 255) pixel = 255;
			ptr[0] = (byte)pixel;

			pixel = ptr[1] / 255.0;
			pixel -= 0.5;
			pixel *= contrast;
			pixel += 0.5;
			pixel *= 255;
			if (pixel < 0) pixel = 0;
			else if (pixel > 255) pixel = 255;
			ptr[1] = (byte)pixel;

			pixel = ptr[2] / 255.0;
			pixel -= 0.5;
			pixel *= contrast;
			pixel += 0.5;
			pixel *= 255;
			if (pixel < 0) pixel = 0;
			else if (pixel > 255) pixel = 255;
			ptr[2] = (byte)pixel;

			ptr += 3;
		}
	}

	bmp.UnlockBits(bmpData);
}
								

Example

									Bitmap b = (Bitmap)Image.FromFile("rose.jpg");
ApplyContrast(ref b, 30);