Call UnregisterGraphicClass to make a graphic class unavailable to all picture objects. UnregisterGraphicClass reverses the registration accomplished by the RegisterFileFormat, or RegisterFileFormatRes, or RegisterClipboardFormat method. When a graphic class is registered, the global GraphicFilter, GraphicExtension, and GraphicFileMask functions can return dialog filter strings, default file extensions or file filters for the graphic class. Call UnregisterGraphicClass when these values should not be available. For example, component writers who implement custom graphic classes unregister those classes in the finalization block of the unit that implements the custom class (Delphi) or using the #pragma exit directive (C++).  

File formats and clipboard formats for the custom class are registered in the initialization block (Delphi) or using #pragma startup (C++). 

RegisterFileFormat