17 aug 2007 kl. 21.22 skrev ADavidhazy:
Hi Per,
Interesting ... interesting ... so this means one can't estimate how
good a final print will be by an approximation provided by the CRT
screen and one should just make sure to meet the printer's "rule" and
that is it. That is no fun. Booo Hooo!
C´mon, Andy, cheer up! :-)
There are two different things, really. First, the question whether
or not the device that produced the image file did make good use of
the amount of pixels available: this is what you can assess on a
monitor at 100% (and give some help with noise suppression and
sharpening if needed). If everything is OK, then the image could
(loosely) be said to contain as much info as the total number of
pixels can accomodate.
Next step, you´re using that file to make a paper print to look at.
Now, the question is: will the total number of pixels be sufficient
for the print size I want? A small print you´ll probably hold in
your hand and peruse closely, a larger one might get framed and hung
on a wall, and a huge one might end up as a poster seen across the
street.
In all these cases, if you come close to seeing individual pixels at
the viewing distance you use, the print resolution isn´t sufficient
for the purpose at hand. If you don´t see pixels, you´ll see all the
detail your eyes could receive, and the print resolution is high enough.
Obviously, this limit has both an individual component (how good is
your eyesight), and a distance dependence (if 300 ppi is enough at 25
cm, 30 ppi would be equally enough at 250 cm). As you know far
better than I, there are formulae that give the theoretical angular
resolution for a given aperture (your pupil diameter), and if you
know the viewing distance, the linear resolution can easily be computed.
Simple? Of course not; nobody in his right mind goes through all
this. Instead, we use empirical rules, like "don´t make small prints
at less than 300 ppi". No fun? Maybe not; the fun was in preparing
the image file, and is in seeing the final print (if all went
well...). Isn´t that fun enough?
Per Öfverbeck
http://ofverbeck.se
"In a world without walls or fences, who needs Windows or Gates?"
