[at-l] Megapixel Madness

[shane@theplacewithnoname.com (Shane Steinkamp)]

Here's another one for the camera thread.  I found it of interest.
I just pray that the copyright gods forgive me...

Shane

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Outdoor Photographer (an EXCELLENT magazine, with a low subscription rate -
www.outdoorphotographer.com) November 2002, page 30.

Megapixel Madness

Q: You state that a 3-to-4 megapixel camera will allow you to make 8x10 inch
prints.  This follows the manufactureuers recommendations, but is
contradicted by a later statement, "The 300 ppi setting (for image
resolution) is conservative, but always works."  My calculator says that to
get an 8x10 inch print with an image at 300 ppi, you need ... 7.2 megapixels
... well beyond the 10 percent stretch factor that some consider a limit.
Can you explain?

A: All of the math is correct, believe it or not, even though some of it
contradicts things.  The 300 dpi/ppi image resolution number is definitely
conservative.  Most printers will give superb results at 240 dpi, which will
increase print size.  You can then get an excellent 8x10 inch print from an
image file of about 12 to 13 MB depending on how it's cropped.  This is
slightly larger than a 4 megapixel camera file (opened and uncompressed, not
the JPEG or RAW file on the memory card) and even more so compared to 3
megapixels.

There's a catch, sort of, Digital camera files enlarge better than scanned
files.  The first time I heard that, I was skeptical, but it came from a
highly respected digital camera guru, Andrew Rodney, who supported it with a
lot of great examples.  I tried it and found it very true.  In other words,
while it's difficult to make a 9 megabyte scanned file look as good enlarged
to the needed 13 to 18 megabytes for an 8x10 print, a 3 megapixel camera
with a similar file size does enlarge quite nicely to 8x10 and even beyond.

The trick is to do the enlargement in your image-processing software so that
you get enough pixels to print properly at 240 to 300 dpi for the 8x10.

...

Doing this, I've made 8x10s form 3-4 megapixel cameras that easily match
35mm prints at that size.  I've seen bigger prints that George Lepp has done
from similar files that also match 35mm prints.

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Shane