9-slice scaling

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Top: Traditional scaling, corners are distorted. Bottom: 9-slice scaling, corners aren't distorted.

9-slice scaling (also known as Scale 9 grid, 9-slicing or 9-patch) is a 2D image resizing technique to proportionally scale an image by splitting it in a grid of nine parts.[1]

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[edit]

The concept was first introduced in a consumer application by Macromedia in Flash 8 (2005).[2] and it was available as feature to scale symbols. Later on, in 2007 Adobe introduced it as a feature in Adobe Fireworks CS3,[3] Adobe Illustrator, and Adobe Flash.[4] Today it is also present as a feature of game development software like Unreal engine, Bevy, Urho3D, and Unity 3D.[5]

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[6] by using the border-image property.

27-slice scaling[edit]

The concept used in 9-slice scaling can be extended to 3D, which enables a more natural way of scaling certain 3D meshes. The number 27 is derived by splitting a cuboid into 3 sections on all 3 axes.

The general method of scaling remains the same, whereby the 8 corners of the cuboid do not scale, similar to the 4 corners present in 9-slice scaling. The central core scales in 3 dimensions. The 6 faces of the cuboid scale in 2 dimensions. The remaining 12 edge pieces scale in 1 dimension. All of which are relative to the actual scaling applied.

A functional implementation is done in Unity as a downloadable package.[7]


  1. ^ "9-slice scaling explained". Lynda.com - from LinkedIn. Retrieved 2018-06-17.
  2. ^ "Macromedia - Flash : Flash 8 Release Notes". www.adobe.com. Retrieved 2017-10-08.
  3. ^ "Improved 9-slice scaling in Fireworks". www.adobe.com. Retrieved 2017-10-08.
  4. ^ Karlins, David (May 7, 2007). "Flash CS3 Professional". Macworld. Retrieved 2018-06-17.
  5. ^ Technologies, Unity. "Unity - Manual: 9-slicing Sprites". docs.unity3d.com. Retrieved 2017-10-08.
  6. ^ Bos, Bert; Etemad, Elika J.; Kemper, Brad (2014-09-09). "CSS Backgrounds and Borders Module Level 3". www.w3.org. Retrieved 2017-10-08.
  7. ^ "Getting Started | 27 Slicer Documentation". Retrieved 2023-05-10.