The whole question of lens sharpness...

Started 10 months ago | Discussions thread
Alphoid
Senior MemberPosts: 1,944
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Re: The whole question of lens sharpness...
In reply to olliess, 10 months ago

olliess wrote:

but it is difficult to see how they would apply.

Compare the heat/diffusion kernel to the (model) blur function of a lens.

I don't think those laws say what you think they say. You're using (or occasionally inventing) big words without understanding them.

There is no such thing as a 'diffusion-type process.' The blur of a lens is simply a convolution with the PSF of the lens. If the PSF is exactly known, it can be exactly inverted with a deconvolution.

First off, the problems of finite bandwidth, limited image extent, and noise will limit your ability to invert. And even you assume the PSF of the lens is known perfectly as a function of distance to the subject, it seems a stretch to assume that you know the distance to every point in the unblurred image.

The only bandwidth limit is the Nyquist frequency of your sensor. Limited image extent doesn't matter. You don't need to know the distance -- you only need to know the PSF at the focal distance. You're trying to improve lens sharpness, not increase DOF. Noise gets amplified -- I mentioned that -- but it doesn't limit your ability to invert. It's a linear process.

The practical limits are:

  1. The PSF has to be very well known.
  2. The image should be at low ISO (otherwise, you'll clean up the image, but also boost the noise to an unacceptable extent).

Otherwise, it can be inverted to the degree it is known.

That's a far cry from a theoretically-guaranteed inversion.

It's exactly what I wrote in my original post.

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