Threshold

This algorithm converts specified image to binary image that has only two colors black and white.

   

• C#
• VB.Net

									Public Shared Sub ApplyThreshold(ByRef bmp As Bitmap, thresholdValue As Short)
	Dim MaxVal As Integer = 768

	If thresholdValue < 0 Then
		Return
	ElseIf thresholdValue > MaxVal Then
		Return
	End If

	Dim bmpData As BitmapData = bmp.LockBits(New Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb)
	Dim TotalRGB As Integer
	Dim ptr As IntPtr = bmpData.Scan0
	Dim stopAddress As Integer = CInt(ptr) + bmpData.Stride * bmpData.Height

	While CInt(ptr) <> stopAddress
		TotalRGB = CInt(Marshal.ReadByte(ptr)) + CInt(Marshal.ReadByte(ptr + 1)) + CInt(Marshal.ReadByte(ptr + 2))

		If TotalRGB <= thresholdValue Then
			Marshal.WriteByte(ptr + 2, 0)
			Marshal.WriteByte(ptr + 1, 0)
			Marshal.WriteByte(ptr, 0)
		Else
			Marshal.WriteByte(ptr + 2, 255)
			Marshal.WriteByte(ptr + 1, 255)
			Marshal.WriteByte(ptr, 255)
		End If

		ptr += 3
	End While

	bmp.UnlockBits(bmpData)
End Sub
								

Example

									DIm b As Bitmap = CType(Image.FromFile("rose.jpg"), Bitmap)
ApplyThreshold(b, 400)