From: jgd@dixie.com (John De Armond)
Newsgroups: rec.photo
Subject: Re: Photo-CD - THE FACTS
Date: 2 Sep 92 08:37:56 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.

tomh@wes.on.ca (Tom Haapanen) writes:

>jay@metran.UUCP (Jay Ts) writes:
>> 3072 x 2048 is *great* for a computer, but compared even to the lowly
>> 35mm format, it amounts to only 85.33 pixels/mm in the 24mm x 36mm frame.
>> Since a "line" is 2 pixels wide (including the space between) this is only
>> 42.67 lines/mm.

>[ ...and Jay goes on to show that this is really poor resolution compared ]
>[ to just about any 35mm film out there.  Not to mention medium format... ]

Film resolution by itself is practically meaningless.  What is needed is
the SYSTEM resolution of typical paper/enlarger/development processes 
for prints and the projection system for slide.  

>All right, I won't argue with that.  But I'd argue that it's not the intent
>of Photo CD to compete with medium format, or even with high-quality 35mm.
>Realistically, what's an acceptable resolution?

Comparing digital and film resolution is at least somewhat like comparing
apples and oranges.  Film resolution is limited by analog features
such as grain size, a feature with no digital analogue unless the scanner
electronics are noisy).  Whereas defects like aberration are what I call 
regional effects in that a defect spans a region of grains, the flying spot
scanner and digital reproduction limit defects to particular pixels.
The end result is a digital of sufficient color depth will look way sharper
than the indicated pixel rate.  Even a 48 bit color, 300 ppi print
is sharp enough that digital artifacts are barely visible to the naked
eye.  600 ppi looks good even under low magnification.  

What is good enough?  Depends on the application.  Newspapers, usually
the lowest quality printing, use 65-85 line per inch halftone screens.
Most non-fine art magazines use 133 line screen.  I use 150 line
screens in PE.  "Fine art" is considered to start around 200 line screen.
250-275 line screen is pushing the physical limits of high speed printing
and is normally not used for production work.

Is the kodak system good enough for any magazine publication?  Presuming
35 mm film and the stated Kodak resolution, Absolutely.  Assuming
the same resolution is carried over to medium or large format, it will
be good enough for even fine art reproduction.

As to prints made with the Kodak system, after seeing and handling a
sample, I suspect that even a pro will not be able to tell the difference
between a digital print and a photographic print without magnification.
The "paper" feels just like RC coated print paper.  

One other thing should be kept in mind.  For really large reproduction,
there are many places that will take your high resolution images and
print them any size up to billboard size.  Obviously the quality
will not be photo-grade but on the other hand, a billboard-sized
print is not really feasible, even assuming paper that big could be
bought.

John
-- 
John De Armond, WD4OQC               |Interested in high performance mobility?  
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