Re: Scanning Resolution

[Valburg <lkv1@psu.edu>]

At 12:46 PM 8/4/99 -0400, you wrote:
>
  I'm told no photographic paper has resolution 
>better than 200 dpi, so scanning it at 300 dpi will not buy you anything, 

I've heard this before, and always wondered whether it was one of those
cases where those who aren't fussy say there's no real difference and those
who are fussy say there's a very real difference.  So I checked it out. 

THE PRINT:  6" x 9" photographic print on Ilford Ilfobrom, enlarged using
either a Schneider Componon or a Leitz Focotar enlarging lens.

THE NEGATIVE:  B&W, probably Tri-X developed in Ilford ID-11plus.

THE CAMERA:  probably my Leica M-3/35mmSummicron, definitely on a tripod.

THE SCANNER:  Microtek x6EL.

THE SCANS:  150ppi, 200ppi, 300ppi, 400ppi, 600ppi, 1200ppi.

RESULTS:  

There are clear gains in information up to 600 ppi.  At every level below
that, pixellization obscures details which are clear in a higher rez scan.  

Comparing the 600ppi (optical max) to the "1200" ppi (stepper motor max) at
the highest magnification before pixellization becomes visible, there's
little to choose between the scans:  very slight difference which falls
into the resolution/accutance pattern described recently by Arnold Gassan.
That is, the higher rez scan (1200) looks a wee tad softer, but with a wee
tad more detail (maybe); the lower rez scan looks a wee tad "sharper," that
is, harder edged, but (maybe) losing just a wee tad of detail.

Comparing the 600ppi and 1200ppi scans at the lowest magnification which
shows any pixellization in the 600ppi, it's clear that extremely subtle
shapes are obscured by pixellization, but unclear whether the greater
detail in the 1200ppi scan is "real" information of simply the lack of
visible pixel edges (that is, whether the interpolation involved at the
stepper motor's maximum resolution is just averaging).

Remember this is a scan of an enlargement from 35mm, made from a Tri-X neg:
 hardly the last word in fine detail (although the lenses and technique
were very good).  One of these days, I'll dig out a 4x5 neg, make a contact
print, and repeat the comparison.  My suspicion, based on the perceptual
difference between enlarged 35mm Tri-X and a 4x5 contact print at the eye's
level of magnification, is that there well be clear, scan-able detail
available at over 600ppi.

Is this level of detail visible to the naked eye?  Certainly, but those of
you familiar with larger format photography know that the difference is
often described less at the gross level of, "see, there's a blade of grass
on the contact print that you can't see on the enlargement" than it is at
the more subtle level of, "see, the contact print just looks more real,
more modelling, more real textures" etc.  Is this level of detail
important?  That's an aesthetic question, and depends on the image, intent,
etc.

But back to the original question:  can there be detail in a photographic
print finer than 200ppi/dpi?  Unless there are flaws in my methodology I
haven't thought of, the answer to my eyes is a clear yes.

Regards,
Mitch Valburg



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