public event ThumbnailLoadEventHandler BeforeThumbnailLoad
Public Event BeforeThumbnailLoad As ThumbnailLoadEventHandler
Handle this event to override the thumbnail load process. By setting the Image property of the ThumbnailLoadEventArgs, you can load the image with customized decoder settings. If you are using a custom decoder that has a special method for obtaining thumbnails, write the thumbnail load code in this event handler.
The event can also be used to obtain a reference to the ProgressEventHandler for the image being loaded in order to show progress of each thumbnail as it's loaded.