The Sharpen Texture Extension

The Sharpen Texture Extension

This section discusses the sharpen texture extension, SGIS_sharpen_texture. This extension and the detail texture extension (see "The Detail Texture Extension") are useful in situations where you want to maintain good image quality when a texture must be magnified for close-up views.

When a textured surface is viewed close up, the magnification of the texture can cause blurring. One way to reduce blurring is to use a higher-resolution texture for the close-up view, at the cost of extra storage. The sharpen texture extension offers a way to keep the image crisp without increasing texture storage requirements.

Sharpen texture works best when the high-frequency information is used to represent edge information, for example:

In a stop sign, the edges of the letters have distinct outlines, and bilinear magnification normally causes the letters to blur. Sharpen texture keeps the edges crisp.
In a tree texture, the alpha values are high inside the outline of the tree and low outside the outline (where the background shows through). Bilinear magnification normally causes the outline of the tree to blur. Sharpen texture, applied to the alpha component, keeps the outline crisp.

Sharpen texture works by extrapolating from mipmap levels 1 and 0 to create a magnified image that has sharper features than either mipmap.

Using the Sharpen Texture Extension
Sharpen Texture Example Program
New Functions