9-slice scaling (also known as Scale 9 grid or 9-slicing) is a 2D image resizing technique to proportionally scale an image by splitting it in a grid of nine parts.
The key idea is to prevent image scaling distortion by protecting the pixels defined in 4 parts (corners) of the image and scaling or repeating the pixels in the other 5 parts.
A variation of the concept, the 3-slice scaling, consists in a grid of 3 parts in which only the pixels in 2 parts (the edges) are protected and the pixels on the middle part are repeated.
History and use
The concept was first introduced in a consumer application by Macromedia in Flash 8 (2005). and it was available as feature to scale symbols. Later on, in 2007 Adobe introduced it as a feature in Adobe Fireworks CS3, Adobe Illustrator, and Adobe Flash. Today it is also present as a feature of game development software like Unreal engine, Urho3D, and Unity 3D.
The technique can be used to manipulate both bitmap/raster graphics and vector graphics. A current implementation of the 9-slice technique is present on the CSS 3 Backgrounds and Borders spec by using the border-image property.
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- Bos, Bert; Etemad, Elika J.; Kemper, Brad (2014-09-09). "CSS Backgrounds and Borders Module Level 3". www.w3.org. Retrieved 2017-10-08.