Comments below.
At 8:11 PM +0000 3/14/03, olympus-digest wrote:
>Date: Fri, 14 Mar 2003 11:16:13 -0800
>From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
>Subject: Re: [OM] A conspiracy?
>
>On Friday, March 14, 2003, at 09:58 AM, John Cwiklinski wrote:
>
> > Joe Gwinn wrote:
> >
> >>>
> > The theory does still hold. Nor was it nonsense back then.
> >
> > The issue is that if the resolution of the lens much exceeds the
> > spacing between pixels (of the same color), it will allow moire beats
> > (seen as color fringes) to happen whenever the pitch of some pattern
> > in the subject happens to be more or less the same as and aligned with
> > the pixel pattern of the CCD.
> >
> > In mathematical terms, what's happening is that the CCD "undersamples"
> > the pattern in the subject, causing "aliasing" (those beats), and the
> > only solution is to "low-pass filter" (blur) the image hitting the CCD
> > chip. The necessary blurring can be done in a number of ways.
> > <<
> >
> > I am not disagreeing with you Joe et al, but it would seem that an
> > algorithm (software) would be able to sense and compensate to correct
> > this problem, thereby making the "better" slr lens more practical for
> > digital.
> >
> > John Cwiklinski
John - It's pretty hard to do with software, as the information necessary to
solve the problem is simply not in the undersampled image. The original issue
was that the aerial image had finer resolution (more information) in it than
the CCD could handle. Aliasing is a consequence of the loss of information due
to the resulting undersampling (too few samples to fully capture the image).
Blurring the image reduces the amount of information in a way not vulnerable to
aliasing, thus surpressing the fringes.
>And it does seem odd that despite all the softening and/or bleeding
>techniques mentioned there is a lot of evidence that digital is
>producing images as resolved as those from film. Certainly plunking
>film designed lenses onto Nikon or Canon DSLRs does not seem to be
>resulting in horrible moire effects or soft images. To the contrary at
>least some digital practitioners are saying that digital shows up the
>limitations of lesser lenses to the degree that one should pop for the
>best lens you can get.
Windsor - The physics are correct. All it takes is for the digital camera,
even with the slight blurrring needed to prevent fringing, to have at least as
much resolution as comparable film cameras. All it takes is money.
Joe Gwinn
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