DirectCast not working - vb.net

Question

'ofd is open file dialog
Dim img As Bitmap
Dim iscmyk As Boolean
Dim i As String
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
ofd.Filter = "Jpg Image(*.jpg)|*.jpg"
If ofd.ShowDialog = Windows.Forms.DialogResult.OK Then
img = Bitmap.FromFile(ofd.FileName)
iscmyk = ((DirectCast(img.Flags, Imaging.ImageFlags) And Imaging.ImageFlags.ColorSpaceCmyk) = Imaging.ImageFlags.ColorSpaceCmyk)
End If
img = New Bitmap(img, New Size(120, 190))
MsgBox("cmyk = " & iscmyk)
PictureBox1.Image = img
End Sub
i need to check if the image is cmyk or rgb
if its cmyk then iscmyk returns true
if its not cmyk then iscmyk returns false
in my windows 7 pc its returns false for each & every image
but in XP it returns perfect answer
why its not working in my other win7 pcs???

Answer 1

First, sorry for responding so late...
Second, actually I don't know
why you get different results on different OS versions.
Anyway, here is a low-level (and ugly) workaround. It's designed for JPEG images:
Public Shared Function GetJpegBpp(FileName As String) As Integer
Dim len As Integer
Dim fp As FileStream = Nothing
Dim marker(1) As Byte
Dim data(15) As Byte
Dim components As Byte = 0
GetJpegBpp = -2
Try
fp = New FileStream(FileName, FileMode.Open, FileAccess.Read)
GetJpegBpp = -1
If fp.Read(marker, 0, 2) < 2 OrElse marker(0) <> &HFF OrElse marker(1) <> &HD8 Then Exit Function
Do
If fp.Read(marker, 0, 2) < 2 OrElse marker(0) <> &HFF OrElse (marker(1) > 1 And marker(1) < &HC0) Then Exit Function
If (marker(1) < &HD0 Or marker(1) > &HD9) AndAlso marker(1) > 1 Then
If fp.Read(data, 0, 2) < 2 Then Exit Function
len = (CInt(data(0)) << 8) Or data(1)
len -= 2
If len < 0 Then Exit Function
If (marker(1) >= &HC0) And (marker(1) <= &HC3) Then
If len < 9 OrElse fp.Read(data, 0, 6) < 6 Then Exit Function
components = data(5)
If components = 0 OrElse components = 2 OrElse components > 4 OrElse (components * 3 + 6) <> len Then Exit Function
len -= 6
ElseIf marker(1) = &HDA Then
If len < (4 + 2 * components) Or (fp.ReadByte() <> components) Then Exit Function
len -= 1
End If
fp.Position += len
End If
Loop Until marker(1) = &HDA Or marker(1) = &HD9
If components = 0 OrElse marker(1) = &HD9 OrElse (fp.Length - fp.Position) < 3 Then Exit Function
Catch
Exit Function
Finally
If Not fp Is Nothing Then fp.Close()
End Try
GetJpegBpp = components * 8
End Function
You need to replace this line
iscmyk = ((DirectCast(img.Flags, Imaging.ImageFlags) And Imaging.ImageFlags.ColorSpaceCmyk) = Imaging.ImageFlags.ColorSpaceCmyk)
with this:
iscmyk = (GetJpegBpp(ofd.FileName) = 32)
Finally, I haven't tested this code with CMYK JPEG images, but I guess it should work...