HOWTO: Make Monochrome Images

Private Function HslToRgb(ByVal h As Double, ByVal s As Double, _
   ByVal bmp As Aurigma.GraphicsMill.Bitmap) As Aurigma.GraphicsMill.Bitmap

	Dim bitmapData As Aurigma.GraphicsMill.BitmapData = bmp.LockBits()
	Dim stride As Integer = bitmapData.Stride
	Dim pointer As IntPtr = bitmapData.Scan0
	Dim pixelSize As Integer = bitmapData.BitsPerPixel / 8

	Dim newBmp As New Aurigma.GraphicsMill.Bitmap(bmp.Width, _
               bmp.Height, Aurigma.GraphicsMill.PixelFormat.Format24bppRgb)
	Dim newBitmapData As Aurigma.GraphicsMill.BitmapData = newBmp.LockBits()
	Dim newPointer As IntPtr = newBitmapData.Scan0
	Dim newStride As Integer = newBitmapData.Stride

	Dim colors(pixelSize - 1) As Byte
	Dim lChannel As Double
	Dim hChannel As Double
	Dim sChannel As Double

	Dim j As Integer = 0

	For i As Integer = 0 To bitmapData.Height - 1
		j = 0
		Do While j < bmp.Width
			System.Runtime.InteropServices.Marshal.Copy(IntPtr.op_Explicit(pointer.ToInt32()+ _
                        i * stride + j * pixelSize), colors, 0, pixelSize)
			Dim blue As Byte = colors(0)
			Dim green As Byte = colors(1)
			Dim red As Byte = colors(2)

			Dim lightness As Byte = (30 * blue + 59 * green + 11 * red) / 100

			lChannel = lightness / 255.0
			hChannel = h
			sChannel = s

			Dim v, r, g, b As Double

			r = lChannel   ' default to gray
			g = lChannel
			b = lChannel
			v = IIf((lChannel <= 0.5), (lChannel * (1.0 + sChannel)), _
                       (lChannel + sChannel - lChannel * sChannel))

			If v > 0 Then
				Dim m, fract, vsf, mid1, mid2, sv As Double
				Dim sextant As Integer

				m = lChannel + lChannel - v
				sv = (v - m) / v
				hChannel *= 6.0
				sextant = CInt(hChannel)
				fract = hChannel - sextant
				vsf = v * sv * fract
				mid1 = m + vsf
				mid2 = v - vsf
				Select Case (sextant)
					Case 0
						r = v
						g = mid1
						b = m
					Case 1
						r = mid2
						g = v
						b = m
					Case 2
						r = m
						g = v
						b = mid1
					Case 3
						r = m
						g = mid2
						b = v
					Case 4
						r = mid1
						g = m
						b = v
					Case 5
						r = v
						g = m
						b = mid2
				End Select
			End If

			colors(2) = Convert.ToByte(r * 255.0F)
			colors(1) = Convert.ToByte(g * 255.0F)
			colors(0) = Convert.ToByte(b * 255.0F)

			System.Runtime.InteropServices.Marshal.Copy(colors, 0, _
              IntPtr.op_Explicit(newPointer.ToInt32() + i * newStride + j * pixelSize), pixelSize)
			j = j + 1
		Loop
	Next i
	bmp.UnlockBits(bitmapData)
	newBmp.UnlockBits(newBitmapData)
	Return newBmp
End Function