Recompress an existing PDF using color detection in VB.NET

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'We assume that GdPicture has been correctly installed and unlocked.
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Dim oGdPicturePDF As New GdPicturePDF()
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oGdPicturePDF.SetCompressionForBitonalImage(PdfCompression.PdfCompressionJBIG2)
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oGdPicturePDF.SetCompressionForColorImage(PdfCompression.PdfCompressionJPEG)
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Dim oGdPictureImaging As New GdPictureImaging()
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Dim status As GdPictureStatus = oGdPicturePDF.LoadFromFile("c:\input.pdf", True)
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If status = GdPictureStatus.OK Then
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    Dim PageCount As Integer = oGdPicturePDF.GetPageCount()
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    For Page As Integer = 1 To PageCount
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        oGdPicturePDF.SelectPage(Page)
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        For Image As Integer = 1 To oGdPicturePDF.GetPageImageCount()
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            Dim imageID As Integer = oGdPicturePDF.ExtractPageImage(Image)
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            If oGdPicturePDF.GetStat() = GdPictureStatus.OK Then
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                oGdPictureImaging.ColorDetection(imageID, True, True, True)
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                If oGdPicturePDF.ReplaceImage(oGdPicturePDF.GetPageImageResName(Image - 1), imageID, False) <> GdPictureStatus.OK Then
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                    MessageBox.Show("Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error)
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                End If
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                oGdPictureImaging.ReleaseGdPictureImage(imageID)
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            Else
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                MessageBox.Show("Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error)
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            End If
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        Next
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    Next
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    status = oGdPicturePDF.SaveToFile("c:\output.pdf", True)
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    If status = GdPictureStatus.OK Then
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        MessageBox.Show("Done!", "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Information)
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    Else
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        MessageBox.Show("The PDF file can't be saved. Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error)
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    End If
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    oGdPicturePDF.CloseDocument()
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    oGdPictureImaging.Dispose()
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Else
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    MessageBox.Show("The PDF file can't be loaded. Error: " + status.ToString(), "Color Detection Example", MessageBoxButtons.OK, MessageBoxIcon.Error)
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End If
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oGdPicturePDF.Dispose()