Brightness Property
Returns or sets the brightness of the specified picture or OLE object. The value for this property must be a number from 0.0 (dimmest) to 1.0 (brightest). Read/write Single.
expression.Brightness
expression Required. An expression that returns one of the objects in the Applies To list.
Example
This example sets the brightness for shape one on myDocument.
Shape one must be either a picture or an OLE object.
Set myDocument = Worksheets(1)
myDocument.Shapes(1).PictureFormat.Brightness = 0.3