See CalculatePalette(UnmanagedImage, int) for details.
public Color[] CalculatePalette( Bitmap image, int paletteSize ) { BitmapData data = image.LockBits( new Rectangle( 0, 0, image.Width, image.Height ), ImageLockMode.ReadOnly, image.PixelFormat ); try { return CalculatePalette( new UnmanagedImage( data ), paletteSize ); } finally { image.UnlockBits( data ); } }