Use this menu selection to convert thumbnails, stored in the current ThumbsPlus database, into JPEG compressed thumbnails. The internal thumbnail data is stored as complete JPEG file stream.
ThumbsPlus will prompt you with the following dialog box, before converting the database thumbnails.
JPEG Quality. Enter a quality value, between 25 and 90. Values below 25 are likely to degrade the image far too much, and values above 90 make the thumbnail storage size larger without any appreciable quality increase.
Compact database after conversion. Check this option to compact the actual database file (MS Access and Sqlite3 database only) after converting the thumbnails. This will release all disk space occupied by deleted or moved thumbnails so it can be used for other files.
See also: File | Database | Compact and Repair.