Matt Ebb has developed a simple setup in the Blender compositor to achieve an Unsharp mask. Unsharp mask is based on calculating the difference of a blurred copy of an image and the original, so he only needed two nodes to create the filter. He then goes on to apply a modified version of the filter to get a fake ambient occlusion effect. Pretty cool stuff!
Matt writes:
Unsharp mask is a popular way of sharpening images, which generally gives much better results and flexibility than simple convolution filters. It may not be widely known, but it’s actually a wet darkroom technique, and is very easy to recreate with some simple blurring and blending. Unsharp mask finds areas of high local contrast by comparing the original image to a blurred version of itself, checks where it differs the most, then uses this mask to enhance constrast in those areas, usually in the luminance channel. The blur radius determines the size, or frequency of features that will be found.
This is quite simple to rig up in the compositor, below is an example with a deliberately grainy and blurry render to clearly show the effect of the unsharp mask.
What caught my eye here is that the compositor is already becoming powerful enough to achieve such specific results. I remember the days back at university when we needed dedicated hardware to do such digital image manipulation calculations ;-)
Link:
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