Re: Scanning resolution for prints

Tanya:

This reply is based on the assumption that you are asking about
physically printing the image on paper or silkscreen, etc.

First, we need to establish if you are simply printing the image
with an ink jet printer or if you are producing images that will
be used to make "plates" for a commercial printing process. The
two are very different.

For ink jet printing, you can use the "default" printer setting
which will be around 80-100 lines per inch. (More about lines per
inch in a minute.) For commercial printing, you will need to
confer with the printer.

In general, the printed world lives with a sort of so-called
resolution that is measured by "Lines Per Inch" or lpi. If you
have a good 8x Lupe you can look at any printed photo and see a
dot pattern. We call them dots, (just to confuse people), but
they are usually little squares. If you went to all the trouble
and measured off an inch and counted the number of dots,
(squares), in that inch remembering that for b/w photos, the
white dots count as well as the black dots, you would have the
number of Lines, (of dots), Per Inch.

The correlation between a laser or ink jet printers "dots per
inch" and the "lines per inch" pattern in the photo is this:

Each one of those little squares (lpi) can be either pure white,
pure black or filled with any number of tiny dots. These are the
dots that come from the printer.

Confused yet?? You should be. Maybe an example would help.

To make the math easy, let us assume you wish to print a b/w
picture that has 100 lpi. This is about what many 1200 dot per
inch printers "default" at.

If we lay out one square inch, we can now divide it up in a sort
of grid that has 100 spaces across and 100 spaces up & down. That
is 100 lines per inch.

However, the printer can produce 1200 individual "dots" per inch.
Either a black spot or a white spot. (No dot) This means that
each of those 100 little squares could have twelve dots across
and 12 dots down. 12x12=144 so we now have 144 different
possibilities in each of those little squares. This is what is
referred to as "shades of gray".

All of the above has to do with printer resolutions. Now--How is
it affected by scanning??

For most purposes, we only concern ourselves with the squares--
the lines per inch. Not the printers 1200 dots per inch. In this
example, the magic number was 100 lpi.

The generally accepted required scanner resolution throughout the
publishing industry is to scan at between 150% to 200% of the
intended lines per inch. In this case, you would scan at between
150 and 200 scanner dots per inch. Any higher is frankly, just a
waste of file size.

HOWEVER

We are talking about the dots per inch at the ACTUAL size the
photo will be reproduced.

If your scanner software shows the final resolution at the
finished size and of course, allows you to set the size of the
finished scan, there is no problem. Just set it to about 150% of
the lines per inch you intend to reproduce.

Otherwise, you have to do the math to be sure that you end up
with the proper amount of dots per inch at the finished size.

I hope I have made this clear enough. I am trying to convey all
the necessary information from several chapters of several
different books and twenty year personal experience in a few
short paragraphs.

Should you care to reply off list with a few "What the heck are
you talking about" questions, I will most certainly understand.

Best wishes
Ted Temer
Temercraft Designs Redding, CA
temer(at)c-zone.net
http://www.temercraft.com
http://www.newsredding.com/


>Hi
>I am sorry if this has been circulated but: could someone tell
me an
>acceptable scanning resolution to use for creating (first) BMP's
and
>then printing (in TIFF or some other format)
>My printer is supposed to have 1440X720 dpi but...
>Thanks in advance!
>Sincerely
>Tanya
>--
>To visit my homepage...(home-made, child-proof)
>http://mypage.ihost.com/tanya (and for more "Art" visit:)
>http://mypage.ihost.com/tanya/PicturesOfPlaces.html
>http://mypage.ihost.com/tanya/Horses.html
>Thumbnails...
>http://mypage.ihost.com/tanya/Thumbnails.html
>

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