Windows thumbnail cache

On Microsoft Windows operating systems, a thumbnail cache is a file used to store thumbnail images for Windows Explorer's thumbnail view. This speeds up the display of images as the smaller images do not need to be recalculated every time the user views the folder.


Windows stores thumbnails of graphics files, and certain document and movie files, in the Thumbnail Cache file, including the following formats: JPEG, BMP, GIF, PNG, TIF, AVI, PDF, PPT and HTML.


Thumbs.db files are stored in each directory that contains pictures or movies on Microsoft Windows NT versions prior to Vista. The file is created locally among the images, however, preventing system wide use of the data and creating additional data load on removable devices. Windows XP Media Center Edition also creates ehthumbs.db which holds previews of video files. Each thumbnail created in a directory is represented in this database file as a small JPEG file, regardless of the file's original format. The images are resized to a maximum of 96×96 pixels, or a proportional miniature of their original shape for non-square images, with 96 pixels on the longer side. Each folder with initiated thumbnail views (that is where they have displayed a Thumbnails or Filmstrip view in Windows Explorer) will have a Thumbs.db file. Folders with pictures also display previews on their icon when displayed in Thumbnail mode – the first four images in the folder at 40×40 pixels (or proportionally shaped), with a 1-pixel divider overlaid on a standard large folder icon. The Thumbs.db file is stored in OLE Compound Document format, the same format that many Microsoft Office products use.


Beginning with Windows Vista, thumbnail previews are stored in a centralized location on the system. This provides the system with access to images independent of their location, and addresses issues with the locality of Thumbs.db files. The cache is stored at %homedrive%Users%username%AppDataLocalMicrosoftWindowsExplorer as a number of files with the label thumbcache_xxx.db (numbered by size); as well as an index used to find thumbnails in each sized database. However, when browsing network shares with write permission, Windows Vista SP1 stores a Thumbs.db file in the remote directory instead of using the (local) central thumbcache.

Resizing the thumbnails

By using Microsoft's own Tweak UI tool, it is possible to alter both the dimensions (up to a maximum of 256 pixels) and the quality of the thumbnails.

See also


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