IncrementBrightness Method
Changes the brightness of the picture by the specified amount. Use the Brightness property to set the absolute brightness of the picture.
expression.IncrementBrightness(Increment)
expression Required. An expression that returns a PictureFormat object.
Increment Required Single. Specifies how much to change the value of the Brightness property for the picture. A positive value makes the picture brighter; a negative value makes the picture darker.
Remarks
You cannot adjust the brightness of a picture past the upper or lower limit for the Brightness property. For example, if the Brightness property is initially set to 0.9 and you specify 0.3 for the Increment argument, the resulting brightness level will be 1.0, which is the upper limit for the Brightness property, instead of 1.2.
Example
This example creates a duplicate of shape one on myDocument and then moves and darkens the duplicate. For the example to work, shape one must be either a picture or an OLE object.
Set myDocument = ActivePresentation.Slides(1)
With myDocument.Shapes(1).Duplicate
.PictureFormat.IncrementBrightness -0.2
.IncrementLeft 50
.IncrementTop 50
End With