Binaryworld - Very simple way to create transparent image using API ... [ VB -> Graphics ]

If you ever need to create transparent BMP then don't worry here is an API which makes your life easy. To make this demo simple I have avoided color selection. In this demo default transparent color is first left top pixel color of source image.

Step-By-Step Example

- Create a standard exe project
- Add 2 picturebox and 3 command button controls on the form1
- Assign Picture to Picture1
- Add the following code in form1

Click here to copy the following block

Private Declare Function TransparentBlt Lib "msimg32" _
    (ByVal hdcDest As Long, _
    ByVal nXOriginDest As Long, _
    ByVal nYOriginDest As Long, _
    ByVal nWidthDest As Long, _
    ByVal nHeightDest As Long, _
    ByVal hdcSrc As Long, _
    ByVal nXOriginSrc As Long, _
    ByVal nYOriginSrc As Long, _
    ByVal nWidthSrc As Long, _
    ByVal nHeightSrc As Long, _
    ByVal crTransparent As Long) _
    As Long

Private Declare Function GetPixel Lib "gdi32" _
    (ByVal hdc As Long, _
    ByVal x As Long, _
    ByVal y As Long) _
    As Long

Private Function MakeTransparentRegion(pbSource As PictureBox, _
                    pbDestination As PictureBox)
  Dim lTransColor As Long

  '//By default take first left-top pixel as transparent color
  lTransColor = GetPixel(pbSource.hdc, 0, 0)

  Call TransparentBlt(pbDestination.hdc, 0, 0, pbSource.ScaleWidth, _
      pbSource.ScaleHeight, _
      pbSource.hdc, 0, 0, _
      pbSource.ScaleWidth, _
      pbSource.ScaleHeight, _
      lTransColor)
  Picture2.Refresh
End Function

Private Sub Command1_Click()
  MakeTransparentRegion Picture1, Picture2
End Sub

Private Sub Command2_Click()
  Unload Me
End Sub

Private Sub Command3_Click()
  Picture2.Cls
End Sub

Private Sub Form_Load()
  'Picture1.Picture = LoadPicture(App.Path & "\test.bmp")
  Command1.Caption = "Start"
  Command2.Caption = "Exit"
  Command3.Caption = "Clear"

  With Picture1
    .AutoRedraw = True
    .ScaleMode = 3
    With Picture2
      .AutoRedraw = True
      .ScaleMode = 3
      .Width = Picture1.Width
      .Height = Picture1.Height
    End With
  End With
End Sub