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Re: [BKARTS] photo resolution



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          CENTRAL NEW YORK BOOK ARTS: TRADITIONAL TO INNOVATIVE
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In addition to years in the field of graphic design and production, I have
also taught many courses dealing with design and production issues. I now
teach a workshop called "The Digital Book" that deals with some of what (I
think) you are asking about photos. Reproduction of photographs on the
printed page is rather complex, and probably too much so to go into here. I
usually refer my students to books such as  Douglas Holleley's "Digital Book
Design and Publishing." Highly recommended for all aspects of putting a book
together!

 I will try a short explanation (there really isn't one, however) and
apologize in advance for what will undoubtedly be confusing. When you
mention below about the size of the photos being so many pixels by so many
pixels, this has no meaning in the printing world, because what you are
dealing with is PIXELS per INCH, or ppi (also known as dpi or dots per
inch). In order for your numbers to make sense, you would have to know how
many INCHES across the printed photograph is. Then you would divide by the
number of pixels, coming up with the PIXELS per INCH formula. What matters
is how tightly the pixels are packed into the actual measured space, hence
the terms 72 dpi (most monitors use this one); 150 dpi (fine for most laser
printers) or 300 dpi (usually best for professional offset reproduction and
printing.

A good rule of thumb is to scan photos (or digitize them from camera) at 300
dpi at the actual printed size. For example, if you scan a 3x5" photo at a
300 dpi resolution, the result will be 900x1500. This is smaller than what
you list below, and yet 300 dpi is plenty for 99.99% of printing purposes.
The reason I mention about actual printed size is that if you enlarge the
photo (say you go from 3x5 to 6x10) you will drop the resolution in half,
and therefore you'd need to scan the original at 600 dpi to end up with 300
dpi at the enlarged size. If you reduce a photo, you can scan at lower
resolution, and so forth.

Another rule of thumb is to find out how fine the printer's HALFTONE screen
is and double that number to get the required resolution. The halftone
screen is formed when a photograph is printed. Since printing presses (and
even ink jet or laser printers) can only print "ink or not ink" they can
only simulate the type of continous tone that an original photograph
possesses. To give the illusion of continuous tone, the image is broken up
into dots. Smaller dots appear to be lighter (more paper shows through)
while larger dots appear to be darker. (These "dots" are not the same as the
dots or pixels mentioned above.) Halftone dots are usually referred to in
"lines per inch" and the more lines per inch, the finer the halftone and the
smoother and nicer the printed photo will be. Newspapers use about an 85-100
lpi because the web presses and course paper will cause ink spread and finer
halftones will be lost and muddy. Offset printers can use higher halftone
screens, depending on the press and the paper. The highest "normal" halftone
is about 150 lpi, although improved printing processes are making finer
halftone screens more prevalent. This is limited to the very high end of
printing, however, and most printers work with 150 even with coated paper.
If you take the rule of thumb formula (150x2) you get 300 dpi, which is the
ideal resolution. Anything over 300 dpi is wasted, and only makes the file
size larger than necessary.

Confused yet?? Here's another head twister. Sometimes scanning software and
programs like Photoshop give the illusion that you can raise resolution, but
that is actually not true. If you scan an image at 150 dpi and then "up res"
it to 300, you won't have improved the quality much at all. This is what is
known as "interpolated" resolution. It has its uses, but for the most part
think of it as fake.

Now you can see why I usually recommend the books. Another one is Digital
Photos for Dummies, and it has good explanations of the process of using
photographs from digital cameras.


Katie Harper
Ars Brevis Press
Cincinnati, OH
513-233-9588




> From: Raven Regan <raven_regan@YAHOO.COM>
> Reply-To: "Book_Arts-L: READ THE FAQ at http://www.philobiblon.com"
> <BOOK_ARTS-L@LISTSERV.SYR.EDU>
> Date: Wed, 22 May 2002 10:10:04 -0700
> To: BOOK_ARTS-L@LISTSERV.SYR.EDU
> Subject: photo resolution
>
> ***********************************************
> CENTRAL NEW YORK BOOK ARTS: TRADITIONAL TO INNOVATIVE
> See The Exhibition Online, And Order Your Catalog.
> <http://www.philobiblon.com>
> ***********************************************
>
> Greetings book lovers:
>
> I know many of you are very technically minded and
> wonder if you can steer me in the right direction?  I
> am writing a book for commercial production
> (probably)or perhaps self-publishing on some art
> techniques with a basis in photos.  I am not a
> photographer with technical knowhow, but I have some
> very good photos, some taken with film cameras and
> some with digital.  I think, but am not positive, that
> for commercial reproduction processes the photo
> resolution has to be in the 3072 x 2048 range.  My
> digital photos are 1600 x 1200.  I am having some
> difficulty finding this type of information.  I don't
> want the book to be written, all the demos to be done
> and then find that I can't publish it due to
> insufficient resolution of the digital photos. I am
> stalled at this point.
>
> This may be of no interest to the rest of the list,
> but, if you can direct me to the information or
> resource book I need, please contact me off list.
> Thank you!
> Raven Regan
>
>
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      For subscription information, the Archive, and other related
            resources and links go to the Book_Arts-L FAQ at:
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