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Thumbnails are reduced-size versions of pictures, used to help in recognizing and organizing them, serving the same role for images as a normal text index does for words. In the age of digital images, visual search engines and image-organizing programs normally use thumbnails, as do most modern operating systems or desktop environments, such as Microsoft Windows, Mac OS X, KDE, and GNOME.
Some web designers produce thumbnails with HTML coding that makes the user's browser shrink the picture, rather than use a smaller copy of the image. In practice the display size of an image in pixels should always correspond to its actual size, in part because one purpose of a thumbnail image on a web page is to reduce download time. The visual quality of browser resizing is also usually less than ideal.
Displaying hhh significant part of the picture instead of the full frame can allow the use of a smaller thumbnail while maintaining recognizability. For example, when thumbnailing a full-body portrait of a person, it may be better to show the face slightly reduced than an indistinct figure. This has the disadvantage that it misleads viewers about what the image contains, so it is less well suited for searching or a catalogue than for artistic presentations.
In 2002, the court in the US case Kelly v. Arriba Soft Corporation ruled that it was fair use for Internet search engines to use thumbnail images to help web users to find what they were looking for.
- The Denver Public Library Digitization and Cataloguing Program produces thumbnails that are 160 pixels in the long dimension.
- The California Digital Library Guidelines for Digital Images recommend 150-200 pixels for each dimension.
- Picture Australia requires thumbnails to be 150 pixels in the long dimension.
- The International Dunhuang Project Standards for Digitization and Image Management specifies a height of 96 pixels at 72 ppi.
- DeviantArt automatically produces thumbnails that are maximum 150 pixels in the long dimension.
- Flickr automatically produces thumbnails that are a maximum 240 pixels in the long dimension, or smaller 75×75 pixels. It also applies unsharp mask to them.
- Picasa automatically produces thumbnails that are a maximum 144 pixels in the long dimension, or 160×160 pixels album thumbnails.
The term vignette is sometimes used to describe an image that is smaller than the original, larger than a thumbnail, but no more than 250 pixels in the long dimension.
Thumbnails in ArcGIS
Thumbnail is a miniaturized version of a graphics file. A thumbnail can be used as a visual index for larger data or images. You can create thumbnails for your GIS layers and data sources by using the Create Thumbnail button in ArcCatalog. Thumbnails can be viewed from the Contents Tab.