Google| Subject | Re: Lenses and sharpening |
| From | Floyd L. Davidson |
| Date | 2014-09-13 23:47 (2014-09-13 13:47) |
| Message-ID | <87fvfv19d5.fld@barrow.com> |
| Client | |
| Newsgroups | rec.photo.digital |
| Follows | Alfred Molon |
| Followups | Alfred Molon (9h & 46m) |
Alfred Molon <alfred_molon@yahoo.com>wrote:
Alfred MolonAny good optical engineer could work it out, given the right equipment and a fairly fat check.
In article <87k35720r3.fld@barrow.com>, Floyd L. Davidson says...Floyd L. DavidsonAlfred Molon
But probably the most useful would be Richardson-Lucy Deconvolutional sharpening. Using just standard default filters (Gaussian and perhaps exponantial) for the point spread function should work better than other sharpen tools, but it would also be possible to develop a very accurate point spread function for any given specific lens (think of the Hubble Telescope), and that would be very significantly better than other methods.
If the softness is caused by a particular camera-lens combination, is there a way to determine this point spread function with for instance some calibration steps, and then apply the right sharpening/ deconvolution?
That's not a likely route for any but the most serious and well healed.
And in fact using a Gaussian spread will work rather well for a slight defocus problem, for diffraction, and for "haze" from atmosphere.
I don't know for sure, but seem to remember that there is software available that will measure motion blur and might be able to produce a custom point spread function to counter it.
I'm even wondering if this point spread function could be determined from an image (without any previous camera/lens calibration), so that the image processing software can choose the right sharpening algorithm and parameters.Some aspects might be. To really do it right though you'd need to have the lens on an optical bench, or have some very specific design specifications.
But sharpening by inspection using a default Gaussian blur for the point spread function does do a fairly good job of sharpening. I'm sure you can use Google to find software that will let you try it. GIMP can do it with a GMIC plugin.
-- Floyd L. Davidson http://www.apaflo.com/ Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
2014-09-13-
