Set the ArcMap Output Image Quality (OIQ) ratio using Visual Basic

Use the code snippet below:

Code:
Private Sub ResetOutputQualityToBest()

On Error GoTo EH

    Dim pActiveView As IActiveView
    Dim pDisplayTrans As IOutputRasterSettings
    Dim pMxDoc as IMxDocument
    Set pMxDoc = ThisDocument

    ' This will change the setting in the 'File | Page Setup' dialog,
    ' but does not affect each map until the document is reopened...
    Set pActiveView = pMxDoc.PageLayout
    Set pDisplayTrans = pActiveView.ScreenDisplay.DisplayTransformation

    If pDisplayTrans.ResampleRatio <> esriRasterOutputBest Then
        pDisplayTrans.ResampleRatio = esriRasterOutputBest
    End If

    ' ...so we will additionally set the output quality for each map so
    ' the current export works correctly.
    Dim pMaps As IMaps
    Set pMaps = pMxDoc.Maps
    Dim lMapIndex As Long

    For lMapIndex = 0 To (pMaps.Count - 1)
        Set pActiveView = pMaps.Item(lMapIndex)
        Set pDisplayTrans = pActiveView.ScreenDisplay.DisplayTransformation

        If pDisplayTrans.ResampleRatio <> esriRasterOutputBest Then
            pDisplayTrans.ResampleRatio = esriRasterOutputBest
        End If
    Next lMapIndex

    Exit Sub

EH:
    Err.Raise Err.Number, "MapsOnDemand.ResetOutputQualityToBest", Err.Description

End Sub

Code:
tagesriResampleRatioType
1 - esriRasterOutputBest
3 - esriRasterOutputNormal
5 - esriRasterOutputDraft