Returns file extension (without dot) of image format selected by given filter index.

function GetFilterIndexExtension(Index: LongInt; 
                                 OpenFileFilter: Boolean): string;

Imaging (at line 523)

Used filter string is defined by GetImageFileFormatsFilter function. This function can be used with save dialogs (with filters created by GetImageFileFormatsFilter) to get the extension of file format selected in dialog quickly. Index is in range 1..N (as FilterIndex property of TOpenDialog/TSaveDialog)