Convoluted Moose writes:
In theory ( that tricky thing, again), I understand that with full
information on what the lens does to light passing through, the
original may be completely reconstructed. General purpose, non lens
specific deconvolutions can't do anything near that, but it can recover
some >>resolution.
A lot of things that were true for film and optical prints are not
the same anymore. Unless adjustments are made, they are often
inaccurate for digital. It's my sense that deconvolution and contrast
adjustments, local and global, add about a stop, so f8 is not, in
effect, >>diffraction limited on 4/3. Even f11 gives away very little I
can see, with the right tools and ability to use them. I've been using
f9 as my default lately. Maybe because I like odd things? Or bumped it
and didn't change it back? ;-)
You make me think it might be interesting to run deconvolution at
different intensities on the color channels. Likely too crude for much
use. Oh dear, am I channeling Mike G? :-)
That reminds me. I still haven't re-compared DxO's lens/sensor
specific deconvolution to FM's generic version. OH well, another day.
Yes, Yes! Please do the latter when it suits. The new version tweaks
the defaults to hit the image with more deconvolution than before
using a slightly improved algorithm.
Would be sure the sliders are adjusted to under-do the image and port
to PS and tweak further there. Can use FM or USM after that as well. I
know which workflow and final image I prefer using the GM-1 and 12-32
at the long end.
Now on the other diffraction issues. I think I am tickled being
channeled but am not sure. I think I should re-post a few things
discussed over months a while ago.
About a year ago my working hypothesis was that even true point-spread
deconvolution will NOT work all that well to fix blur due diffraction
from a small aperture.
Recall from Dr. D's link that on FT sensor by F11 max
resolution is down to about 4MP overall and 3MP
with red light.
http://www.luminous-landscape.com/tutorials/resolution.shtml (see
table 3)
Unlike diffraction blur ,Gaussian blur "leaks" enough high frequency
information into the image that it can be boosted and reconstructed
(indeed, a gaussian is a very special extremum case that results in max
blur for the least loss of high frequency detail)
found the below images--not perfect but good enough
original image:
http://praetoriusphoto.images.s3.amazonaws.com/fmforums/20120322_deconvolution/sinsweep.jpeg
added diffraction:
http://praetoriusphoto.images.s3.amazonaws.com/fmforums/20120322_deconvolution/diffracted_sweep.jpg
note how detail frequencies above the cutoff are almost completely
wiped out.
Gassian blur added:
http://praetoriusphoto.images.s3.amazonaws.com/fmforums/20120322_deconvolution/gaussian_sweep.jpg
note gradual reduciton of high freq info rather than cut-off.
HOWEVER, form a practical vantage point, Moose has always said that
stopping down for dof if required for
the image even past the diffraction threshold should usually be done
though maximal sharpness in the in focus areas may be slightly
compromised. When aperture bracketing when I was previously more
nervous going way past the sweet spot for a lens, empirically the dof
gain almost always offset
the modest diffraction softening (as I don my I agree with
Moose T--shirt) unless the image is turned to mush at very small
apertures. Spotted this more exacting review of the situation :
http://www.lensrentals.com/blog/2013/03/overcoming-my-fentekaphobia
(look at this link if nothing else!)
To quote Roger at Lensrentals from the link:
"The message I took away, though, is that diffraction softening is
real, it occurs where it is supposed to, but it’s really not as severe
as I had thought. Even on the D800 resolution is as high, or higher, at
f/16 than it was at f/2.8. At f/11 the resolution is as good, or
better, than at f/4. And at both f/11 and f/16 resolution is clearly
higher than it was wide open. Perhaps the diffraction monster’s teeth
AREN'T as long and wicked as I thought."
Now look at link at post 66:
http://www.luminous-landscape.com/forum/index.php?topic=45038.60
Yikes, R-L deconvolution didn't do half bad ! Admittingly he used a
perfect PSF but still much of the compromised image data should have
been gone and what is there is distributed over more energies requiring
much more intensive processing at diminishing returns to recover.
So deconvolution CAN improve diffraction softened images ( Canyon's DLO
uses an exact PSF) despite total loss of some high freq image data.
How can that be??????
Deconvolution sharpening can (with non-determinate PSF's) do increase
detail CONTRAST, though you can't really increase the maximum detail
frequency. It gets further confusing in that unfortunately the concept
of resolution has to be very tightly coupled to "contrast", and often
you use MTF50 contrast to get a "resolution" number. The point of real
detail extinction is significantly higher than that.
So FM or DXO Optics Pro away on diffraction softened images and go
ahead and push the aperture up past the diffraction limited thresholds.
Keeping the convoluted in deconvolution, Mike
--
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