Very Computer

What is a good resolution (ppi) i should scan in to have a small file size
with a pretty clear printout on a 600 dpi printer?

600 dpi

Well, I would tend to say that that is too high.  It all depends on the size of line
screen that you are using.  A general rule of thumb is to use between 1.5 and 2.5 times
the line screen as your scanning resolution.  For example, if you are using an 85 line
printing screen, a scan around 150 dpi will be more than adequate (if you are printing at
100% original size).  The printer's resolution has more to do with the ability to print
quality greyscales and smooth blends.  I use a Newgen ImagerPlus12 (1200 x 1200
resolution) and I still only scan at 150 dpi for printouts (assuming you are printing at
100% original size).  If you are printing at 200% of the original size, double the
scanning resolution (300 dpi), 300% triple the resolution (450 dpi), 50% of the original
(85 dpi), etc.

Any questions, feel free to email me.

jeff grant
publisher
spinnaker publishing ltd

Well, I would tend to say that that is too high.  It all depends on the size of line
screen that you are using.  A general rule of thumb is to use between 1.5 and 2.5 times
the line screen as your scanning resolution.  For example, if you are using an 85 line
printing screen, a scan around 150 dpi will be more than adequate (if you are printing at
100% original size).  The printer's resolution has more to do with the ability to print
quality greyscales and smooth blends.  I use a Newgen ImagerPlus12 (1200 x 1200
resolution) and I still only scan at 150 dpi for printouts (assuming you are printing at
100% original size).  If you are printing at 200% of the original size, double the
scanning resolution (300 dpi), 300% triple the resolution (450 dpi), 50% of the original
(85 dpi), etc.

Any questions, feel free to email me.

jeff grant
publisher
spinnaker publishing ltd

You should scan at twice the line screen frequency of your printer.  If
your printer does 100lpi, then scan at 200ppi.  If your printer supports
screens above 133lpi, then you need only scan at 1.5 times the line
frequency for good results.

-Matt

Here's a dumb question I'm afraid... I have a LJ 4M, which prints at
600 dpi, but how do I know what the best screen to use is?  How many
lpi will this machine do?

gs

Before I start I'd like to say that I hardly know anything about graphics
(it's all VERY new to me :-) and what I have to say is going to be
EXTREMELY simplified but it's an excellent rule of thumb (for what I do).
Anyway, I'm a sound designer.  I also do recording on occasion and I've
noticed that people often rely too much on specifications, and "well such
and such said do it this way".  They feel they have to use technique X for
recording drums, and technique Y for recording guitar.  While all of this
is fine when you're getting started (you have to start learning somewhere)
it's a really bad thing to get locked into.  Specs are usually fudged (
any person who buys speakers because the salesperson told them it had a
wide frequency range which can handle compact discs is a person who just
got ripped of, specs are pretty much irrelevant when buying set of
speakers, all that matters is what your ears tell you ) to favor that
piece of equipment anyway.  If you're recording something it pretty much
comes down to one thing which is:

How does the final product sound?

If it doesn't sound good (or the client doesn't like it which is a whole
other can of worms... or even better, it sounds awful and the client likes
it but you don't want to put your name on something that sounds that
awful.... <hehe> ) you have to try something different.  As I said, that
is simplified but most of the time true, so if your ears are the number
one judge with music and sound, then why not let your eyes be the number
one judge with graphics?  Take an acoustic guitar or a sax for example.
There are thousands of different ways to record these instruments
(different mics, different positions, etc.).  To make things even more
insteresting the technique you used for brand X guitar could potentially
sound awful on brand Y. Just a thought, I'd be interested in knowing what
people think about this?

C ya, Joe

--
        When the only tool you have is a hammer,
        everything begins to look like a nail.

        -Lotfi Zadeh

It's not a dumb question, I have also the same question???

--
____________________________________

LABSAP, PEPS                
Laval University              Bonne journee!
Quebec, CANADA                Have a good day!
G1K 7P4
(418) 656-2929

It's not a dumb question. That printer has a default screen ruling of 60LPI.  Changing it to a higher line count is possible within =
some programs, but it reduces the number of gray levels. Sometimes it causes a strange, almost moire effect too, at least on mine it=
 does.

Mike Lawless
Lawless Designs
http://www.valleynet.com/~raceart

Quote:

> It's not a dumb question. That printer has a default screen ruling of

60LPI.  Changing it to a higher line count is possible within =

Quote:> some programs, but it reduces the number of gray levels. Sometimes it

causes a strange, almost moire effect too, at least on mine it=

Quote:>  does.

> Mike Lawless

With the new Laserwriter driver, it seems the default it 85 lpi.  But
what does this mean?  Point me at a good book.<G>

For 85 line screen, use 170ppi scans.  Just double the lpi of your laser
printer, if in doubt.

About grayscale on a laser printer:

Your laser printer approximates grays with a halftone, the same way a
newspaper does it.  A halftone divides a grayscale image into cells.  The
cells are arranged in lines.  85lpi means 85 lines of cells per inch.  The
cells are composed of pixels, black where there is toner, white where
there is no toner.  The number of pixels in each cell determines the
number of grays representable by each cell.  The courser your lpi, the
more grays you get because each cell contains more pixels, and can
approximate more grays.  

How does this relate to your laser printer?  The ppi of your printer
determines the number of grays its halftone can approximate.  A 300ppi
printer with a 60lpi screen can approximate 25 gray levels (300/60 = 5
squared = 25).  A 600ppi printer can approximate 100 gray levels (600/60 =
10 squared = 100).  A film image setter at 2400ppi can represent 1600
levels of gray at 60lpi!  But, rather than do that, which would be a waste
since there are only 256 levels represented in most grayscale images, they
up the screen to 150, for example, diminishing the size of the screen and
giving them 256 gray levels.

So, depending on your image, adjust accordingly.  A high contrast picture
may need fewer gray levels to print well, so you can up the screen and get
higher resolution.  A low contrast image or a full range image, will
benefit from a full range of grays, so lower your screen as far as you can
until the screen becomes unacceptable to you.  

Anothing thing to consider is screen angle.  The lines of a halftone can
be orinted to any angle.  In fact, in color work, the screens for the four
process colors have to be at different angles to avoid moire patterns.
So, if you do get moire patterns in b&w, try adjusting the screen angle so
that it doesn't moire with the image.  Stripes and things like that tend
to misbehave if the screen angle is close to their orientation.

-Matt

...
[re halftone screen settings]
-> With the new Laserwriter driver, it seems the default it 85 lpi.  But
-> what does this mean?  Point me at a good book.<G>
You don't need no stinkin book - the Internet is here to explain halftoning
to you.

Picture a grid of 85 lines per inch turned at an angle and placed on top
of one of your printouts.  This is an 85 line halftone screen.

Each cell is approximately 7 printer dots (pixels) per side: 49 dots/cell,
and 50 different shades of gray per cell.  That's it.

If you make the screen finer, the number of pixels, and therefore the
number of different possible gray values goes down.  If you
make it coarser, the dots become more visible.  There are rules of thumb
for picking the screen size.

You can also play around with it and see what
works the best for a particular picture.  You can also rotate the screen
angle, typically, in the same options box that allows you to set the lpi.
There are also different patterns for turning the dots on and off.  There
are even mathmatically based .

--
http://www.aggroup.com/mgr/

I just called HP about this and got the answer 53lpi! It's HP's
default screen. I tried it and it works better than any higher
screen that I have used.

The formula I have is:

Frequency = resolution (?greylevel - 1)

so, at 600 dpi and 256 greys, gives a 40 lpi screen frequency.

--
Stephen Rea
Macintosh Systems Engineer
Jessi Group, Inc.
716-624-1920

85 lpi is the screen of a 600 dpi Aplle machine with Photograde.