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Re: [OM] Enhance Details

Subject: Re: [OM] Enhance Details
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 20 Feb 2019 20:18:36 -0800
On 2/20/2019 1:19 PM, Wayne Shumaker wrote:
Thanks Moose. Always good to have someone do some leg work I don't have time for.

:-) All the links in my last are stuff I'd done before. As with the Asian Falcon image I recently posted, and the Hooded Merganser Female soon to make an appearance, I am not uncommonly using big crops or 100% pieces out of 800 mm eq. shots of distant critters. So I'm very interested in pixel level resolution, artifacts, etc. Always fussing, trying new software, techniques and so on.

Great insights and analysis.

Thanks! I always hope my efforts will gain value by being of use to others.

I admit I am not familiar with deconvolution sharpening. Someone pointed to the Point Spread Function (similiar to impulse response). How this PSF is determined for the sharpening I don't know and wonder if some optical assumptions are involved or if it is derived from the actual image?

MikeG is our local expert on math and methods. I'm the guy who long ago lost the ability to do that sort of math - and - is an empiricist.

Roughly speaking, there are two kinds of deconvolution processing:

1. The characteristics of a specific lens are known. The software works backwards from the results to what the subject must have looked like before the lens altered it.

Canon uses this approach in their Raw converter for their own lenses. DxO may use it as a part of their "Lens Sharpening" in PhotoLab. I've read conflicting opinions. As they test each lens to develop their distortion correction data, they could also be measuring the PSF. I believe other manufacturers may also be doing this, but don't know.

2. Generalized solutions have been developed that start with some assumptions, alter variables and try to find an optimum by trial and error. The best are very computation intensive, and not practical for day to day photography use.

This is the approach used by the deconvolution examples I posted a link to in my last, Focus Magic and Topaz InFocus. An Adobe developer has said that a limited version is used in PS Smart Sharpen in some cases.

The interesting thing about theory vs. experiment is that, while the math says lost bandwidth cannot be recovered, in practice, deconvolution often recovers detail previously invisible. This may be no more than making visible detail that was already there, but too low contrast for us to see. In any case, it works for "sharpening", generally better than USM.


At the deep end. donning my scuba gear now...


Deep Breath Moose


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