Gas station without pumps

2011 October 11

Optimal defocus estimation—possible explanation for evolution of astigmatism

Filed under: Uncategorized — gasstationwithoutpumps @ 14:46
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I found this article, Optimal defocus estimation in individual natural images, rather interesting, despite being well outside my current field.

The basic idea is a simple one: compute the effect on Fourier transforms of images of defocusing by various amounts, and use modern machine learning techniques to learn filters for detecting the defocusing.  One can get a lot of extra information about the defocus if the lens system is not perfect, using astigmatism and chromatic aberration to get more precise defocus estimates. This paper gave me some insight into why astigmatism has not been eliminated by natural selection.  I had always assumed that it was either not a serious enough defect to have strong selection or that it was linked to other, desirable traits that kept it around in the population.  This paper points out a possible selective advantage to astigmatism, allowing faster focusing in low-light conditions (when the chromatic aberration signal may not be available).

The paper did not go so far as to provide fast algorithms for autofocus using the new technique, but it looks like it might be feasible.  It would be nice to have an autofocus algorithm for digital cameras that did not do so much slow movement of lenses as the current ones use.

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