[at-l] Megapixel Madness--Way Off Topic & Long

[lparker@cacaphony.net (L. Parker)]

> -----Original Message-----
> From: rick boudrie [mailto:rickboudrie@hotmail.com]
> Sent: Saturday, November 09, 2002 11:31 AM
> To: lparker@cacaphony.net; bullard@northnet.org
> Cc: at-l@backcountry.net
> Subject: Re: [at-l] Megapixel Madness--Way Off Topic & Long
>
>
> This is so confusing.  I would have thought that an image
> resolution for
> CMYK photographs of 300 - 350 dpi would have been just fine
> for most any
> magazine or commercial print job, provided that the photo
> would be place in
> the desktop publishing program at 100%.
>
> Rick B

The confusion is mostly due to varying methods of printing rather than a
matter of the camera or image itself.

If you are going to an old style "press" using photographic plates rather
than an imagesetter which uses digital input files, then you need an actual
photo to burn the plates. I don't think there is a photographer out there
that would disagree that slides are superior for this purpose.

A digital imagesetter on the other hand only requires between 1.5 and 2
times the ppi (pixels per inch) of the output line screen, which has to do
with the requirements of half toning, something that most computer printers
such as inkjets don't do. Laser printers use a process similar to
imagesetters and the explanation below applies to them also, but the numbers
may vary.

An example might help to illustrate. Most imagesetters use an output line
screen of 150 lpi (lines per inch) for 2540 dpi output to coated or uncoated
media. This means the ideal input file will be between (150 x 1.5)= 225 ppi
and (150 x 2) = 300 ppi. My Canon S110, which is relatively old, is a 2.1
megapixel camera and produces maximum resolutions of 1600 x 1280 ppi. This
translates to an input file between 7.1" x 5.5" (at 225 ppi) and  5.3" x
4.2" (at 300 ppi). So this means that it would produce image files suitable
for printing in a magazine as long as the size of the final image is equal
to or less than the sizes given above.

This is the point of contention, it is NOT a high enough resolution image to
print a full 8" x 10" image from an imagesetter. Even the newest compact
digitals can only produce an image suitable for 7.5" x 9.5 " imagesetting.
Close, but not quite. You can get output suitable for 8.5" x 11"
imagesetting from cameras such as Canon's EOS D60, but it is not a compact
and it isn't cheap.

Now something like the Canon EOS-1Ds (which isn't technically available yet)
with an 11 megapixel sensor can produce image files (4064 ppi x 2704 ppi)
suitable for up to 12" x 18" imagesetter output. In the graphics industry,
this means it can do a two-page "full bleed" magazine layout at an input
resolution of 225 ppi, an output line screen of 150 lpi and an output
resolution of 2540 dpi. You will remember from earlier posts on this thread
that those numbers are basically the same as what is available from a slide
scanner.

So to wrap up, yes, the digital image from your camera will be usable by the
imagesetter(s) used by most magazine's production departments and almost all
commercial printers, within some output size constraints. Constraints that
are well within the normal needs of most magazines. Will they accept your
digital images? Probably not.

Are we totally confused yet? <G>

Lee I Joe



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