Set IncrementalDisplay to true on large compressed images that take a long time to load or on images that may be altered by a computationally slow process. When IncrementalDisplay is true, partial renderings of the image are drawn periodically during slow operations such as loading. Set IncrementalDisplay to false to wait until the entire operation is complete before drawing the image. 

For some classes of graphic objects, an OnProgress event occurs at various points during slow operations. If IncrementalDisplay is true, the OnProgress event occurs immediately after the approximate image is drawn. If IncrementalDisplay is false, OnProgress occurs but the image is not updated until the entire image has been loaded. 

The default value for IncrementalDisplay is false. 

OnProgress