图片批量变成灰色

Sub 图片批量去色()
    Dim oshp As Shape
    Dim osld As Slide
    For Each osld In ActivePresentation.Slides
        For Each oshp In osld.Shapes
            If oshp.Type = msoPicture Then
                oshp.PictureFormat.ColorType = msoPictureGrayscale
            End If
        Next oshp
    Next osld
End Sub