Re: MP needed for 24x36 print?

Bart van der Wolf wrote:
> "Roger N. Clark (change username to rnclark)" <username@xxxxxxxxx>
> wrote in message news:43A650F1.6070209@xxxxxxxxxxxx
> SNIP
> > In my opinion, one should interpolate to maintain 300 ppi
> > as a minimum.
>
> I agree. 300 ppi equals approx. 5.9 cycles per millimetre, the lower
> threshold of human visual acuity. Having more pixels, to come closer
> to 8-12 cy/mm, is a recipe for utter perfection at any size.
>
> SNIP
> > My work flow was:
> SNIP
>
> > 3) Image Restoration Using Adaptive Richardson-Lucy Iteration in
> > ImagesPlus 2.5, typically 7x7 box, 7 iterations.
>
> Rather than 'giving in' to ImagesPlus' pre-defined PSFs, if you're
> interested, I'd be willing to provide you with an optimized Custom PSF
> that you can use in IP as custom input for the RL restoration.
>
> To allow the creation of the PSF I'd need a .CR2, or a typical 15-16
> b/ch baseline conversion crop of it, of an approx. 5 degree slanted
> edge (e.g. http://www.imatest.com/docs/lens_testing.html#target) that
> was shot with your preferred lens (typical aperture, or best aperture
> at around f/8) on your camera from about 25-50x the focal length
> distance. ISO 100 would give best results, even though you would in
> practice likely shoot at higher settings.
>
> With that I can approximate the PSF that was caused by
> lens+aberrations, AA filter, and sampling density (assuming perfect
> focus, tripod, and mirror lock-up), including PS resampling. It can be
> used as direct input for PSF based restoration algorithms, or as an
> approximation of a high-pass filter for sharpening.
>

It seems to me it would be hard to get the PSF of a system wtih just
one edge. In most lenses the aberrations get much larger as you move
away from the center of the FOV. You also have astigmatism to deal
with, which one edge will not catch.

Scott

.

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