Semantic Depth of Field
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Depth of field is intuitive and preattentive.

Assign relevance factor to each object and blur.

Use consumer-grade texture mapping hardware (scale down for blur).

Examples: blur map layers, blur chess pieces, blur text.

Preattentive perception takes place after about 200 ms.
Parallel, high bandwidth.  Can preattentively detect targets,
locate targets, estimate number of targets present.
Precision depended on the blur level of distractors and
number of distractors.

Distinction between blur levels is difficult; very weak
perception of blur difference.  Blur and orientation not
slower than orientation alone.  Blur not significantly
slower than colour.

Conclusion: SDOF is an effective and efficient focus+context
technique.  Does not distort geometry.  Natural, intuitive,
preattentive.