Returns or sets the contrast for the specified picture or OLE object. The value for this property must be a number from 0.0 (the least contrast) to 1.0 (the greatest contrast). Read/write Single.
Example
This example sets the contrast for shape one on myDocument. Shape one must be either a picture or an OLE object.
Set myDocument = ActivePresentation.Slides(1)
myDocument.Shapes(1).PictureFormat.Contrast = 0.8