> This site covers it well.
> http://www.alpenglowimaging.com/resolution.htm
> Two thirds down talks about the 300 ppi standard.
The writer is making all sorts of assumptions in that. I agree
that 300 ppi (or dpi) is the "standard" resolution for printed
output (depending on various factors, but a good average), but
does this mean that you have to have a one-for-one source to
output pixel?
I maintain that the answer is no. One reason alone should be
enough--the source image isn't pixel-sharp to begin with. You
are butting up against the resolution limits of the lens as well
as the AA filter. So, if you figure a 3-pixel maximum
sharpness, that reduces your maximum resolution to 1/100 of an
inch, not 1/300.
When you start uprezzing (enlarging) the file, this "blur" is
going to also enlarge. Just where is the limit is a matter of
the requirements of the job as well as the viewing distance. As
a general rule, 4x is a good starting point. Why? because an
image file with 300dpi resolution and giving you a full 8x10
(2400x3000) is essentially the same as a contact print from an
8x10 negative. It is generally accepted that you can enlarge a
negative 4x with no visible loss of resolution. This will, of
course, vary depending on several other factors which apply
evenly to all formats and capture methods.
Bill Pearce has expressed that 1:1 is a desirable thing in his
world. That may be true, but I believe that his sharpness
quotient is also based on the rest of his imaging methodology
and tools. If he is maximizing the sharpness of his lenses and
eliminating vibration beyond most photographers, he is getting
down in the "pixel-sharpness" world. This would be where you'd
actually be seeing 1/300 resolution.
In fact, to provide output pixel sharpness, and assuming that
the best we mere mortals can achieve is 3-pixel sharpness, we'd
have to actually feed the printer a 900 dpi file or a downrezzed
file representing that.
AG
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