Not true.

Not unless you're Superman.  Under normal viewing conditions and at
normal viewing distance -- any difference is beyond the limits of human
perception.

Science, eh? Hah! Anyway, it's trivial to test this for anybody owning
a printer.

Your basic point about subject is valid, but I think 0.7 MP (93 PPI)
really is too low to look very good at 8x10 at normal viewing distance
even with a great subject.  From both theory and my own experience, I'd
put the lower bound for good 8x10 at about 1.4 MP, twice your number.

Well I certainly don't disagree that, if you look from far enough, 3mp
is enough for  A4. I, however, certainly don't look at my A4 prints
from 60cm. And I do like as much detail as possible in my prints (but
then again, I am clearly a lousy photographer trying to justify my
equipment).

[]

Agreed.

If you scale the viewing distance to the print size, it's expected that
the resolution requirement remains the same at, from what you've said, at
about 3MP.  However, with bigger prints, people do tend to look at them
relatively closer than for small prints (e.g. holding each at arm's
length), and therefore expect a greater resolution - 6MP or better.

Cheers,
David

Remember, that with anything that is as subjective as photography, each
person will have their own criteria as to what is "good enough". Around
here, we have heard from those who would see an 8x10 print of a scenery shot
of a small town taken from a mountain side and want to be able to use a
magnifying glass to read the headline on a newspaper being read by a man on
his front porch at the far side of town (right?). For those, a 100 gigapixel
image would be barely acceptable. For others a photo of grandpa and the
grand kids playing at the park hanging on the livingroom wall is good if you
can recognize the people in the picture from 8' away. For these a 1 to 1.5
mp image will do fine. With such subjective differences it is very difficult
to put hard numbers to anything that will satisfy everyone. Even if we limit
discussion to a specific set of circumstances such as print size, viewing
distance, etc there will be those who will be very happy with 1mp image, and
others who will say 6mp doesn't present enough sharpness.

Then if you add the problem of subject, things get even more confusing. As
one person mentioned, some "modern art" images could be very easily captured
with 30 to 40 mp, while some highly detailed images are pressing the imaging
limits with 10-12mp.

This is why I (for one) advocate the right tool for the right job. If you
are intending to shoot something that is more of a memory enhancer (such as
the Grandpa and kids photo) you can use a lower resolution camera that fits
in a pocket easily and is so easy to use that you can almost "think" the
photo onto the memory. When you are intending to shoot something for showing
off, a higher res camera with many manual settings is the right tool. And if
your intent is to publish or document some scene where you now or someday in
the future may want to examine almost invisible fine details, the very best
equipment available is the way to go. Each of these uses is a totally valid
use and will somewhat define what is "good enough". There is no "best
camera" or "best resolution", or "best technique" that will cover absolutely
every need and desire.

JMHO

Randy

I wonder if that calculation lay behind the oddly specific 3.1MP of my
Canon Powershot A300? I certainly couldn't spot any failures of detail
or sharpness in A4 prints from that at two feet. At one foot, however,
I could discern the digitisation, and at six inches it was annoyingly
obstrusive.

So how is it that images on my 13 x 10.5 inch display, with all of 1.3MP,
appear perfectly sharp when viewed at 21 inches?  Something to do with the
pixels being sharp?

<G>

David