A few basic tips to improve the quality
of your scans.
Scan photographs as grayscale
In most scanning software, the halftone
scanning function is used for art that
has already been scanned and has a dot
Scan at the right resolution
Most new users scan at too high a
resolution. Too high a resolution will
create huge files and increse processing
time on your rip or your digital printer
Use the correct resolution for the
The scanning resolution for photographs
is different than the resolution for
line art. The resolution for photographs
is a function of the final line screen
that the photo is to be printed at, and
varies depending upon whether the photo
is to be enlarged or reduced.
If you are enlarging a photo 120% and
printing it using 133-line screen, there
is a simple formula you can use:
(line screen) x 1.55 x (enlarge/reduce
percentage) = Scan Resolution.
In this example, the scanning dpi would
be 227 (or as close as it can be) (133 x
1.55 x 1.1 = 227 dpi).
Scanning line art
Line art should be scanned at the
highest possible resolution. Even if
your scanner is only a 300 dpi scanner,
you can interpolate a grayscale scan and
get 1,200 dpi results.
First, scan the art at the highest
resolution your scanner allows. In
Photoshop, choose Adjust>Levels, from
the Image menu. While looking at the
graph of the image, reset the top set of
three sliders. Move the black slider so
that it is just to the right of the peak
of the lift-hand hill on the graph. Move
the white slider so that it is just to
the left of the peak of the right-hand
hill. Click the OK button.
Choose the image Size from the Image
menu. Make sure the File Size check box
is not checked. Without changing the
dimensions of the image, change the
resolution to 1,200 dpi.
Choose Bit map from the Mode menu. Make
sure the Output Resolution is set for
Save the resulting file in TIFF format
with LZW compression.
The scan will have been saved at the
higher 1,200 resolution.
Plan before you scan
Know the size you want the halftone to
be in the finished piece. If you plan to
reduce the image 50 percent, it will
double the resolution. Reducing it 33
percent triples it.
Use a retouching program
Clean up your scan in a retouching
program such as Photoshop before using
it in a layout program. The size and
resolution should be set before placing
them in a layout program.
Crop the image while you are in the
retouching program. White space creates
data in the file and will make the file
larger and take longer to rip or print.
You will want to avoid using Quark or
PageMaker to crop or rotate a scanned
Scan the photo at
the right Gamma
Gamma is a way of expressing changing a
photo’s overall brightness and contrast.
It’s a curve on a graph that changes a
photo according to a number, such as
1.4, 2.2, or 0.8. The number is
shorthand for the curve. It mostly
changes the mid tones of a scan. In most
photographs, the mid tones (the skin,
for example) have most to the important
detail. By either lightening or
darkening these areas, you can bring out
If you make the change as the photo is
scanned in, you will not degrade the
quality of the image by adjusting it. If
you scan a photo in and change the gamma
afterwards, you will lose detail and
tonality in one way or another.
The operator should increase brightness
and contrast for most photos. The most
common problem with desktop scanners is
creating scans that are too dark. Most
scanning software allows you to set
gamma, and you can usually start with a
1.4 gamma and go higher if need be.
If your scanning software doesn’t have a
gamma adjustment, you can use brightness
and contrast controls; increase both for
more gamma, decrease both for less. This
technique will not work quite as well.
Adjust the photo
to boost its tonal range
Make the darkest part of the photo as
black as it can be and the lightest part
as white as it can be, while making a
smooth transition from black to white.
Set the tonal range by using the Levels
dialog. Set the black point slider just
to the left of the end of the graph of
the image, and the white point slider
just to the right of the start of the
Experiment with moving the mid tone
point slider (gray) to improve the image
Be sharp on screen
Make the on-screen image just a little
sharper than you think is needed. It
will soften in production. Use the
Sharpening routine in the retouching
Add Noise to a scan to minimize the
transitional steps between your
grayscales. This technique smoothers a
low resolution scan.
Calibrate your monitor
It is hard to get your monitor to match
the printed piece. One trick for black
and white photographs is to make sure
the screen is giving you a good idea of
the overall contrast of an image.
One calibration suggestion found on the
Internet was to tape a printed version
of a photograph up next to the monitor
and open the image in Photoshop. The
printed piece will show some darkening
and increased contrast.
To determine how much calibration is
needed, use the Printing Inks Setup
dialog (choose Preferences>Printing Inks
Setup from the File menu). Make sure
“Use Dot Gain for Grayscale Images” is
checked, and start with 10% dot gain
(you will have to exit Printing Inks
Setup to see the previewed dot gain).
Try different amounts of dot gain until
the screen is close to the printed
piece. Dot gain will vary from one press
to another. You will have to redo the
process depending on the press used to
produce the work. The press operator can
give the desktop publisher information
on how much dot gain to expect.
Printing Inks Setup changes the way the
image is displayed on the monitor, not
the image itself. This will cause the
photo to look different on another
monitor. After you “calibrate” a
monitor, don’t change the brightness and
When you calibrate any monitor, allow at
least 30 minutes for the monitor to warm
up so you can get a more accurate
Making Images Larger
Enlarging images can be more
problematical. As explained above, when
you enlarge a pixel-based image--in
whatever application you use--you also
enlarge the pixels until you reach a
point when the pixels themselves become
visible to the naked eye. Although
making enlargements in your page layout
or drawing application is less demanding
on disk space and makes output faster,
you may notice loss of output quality if
you enlarge more than about 180%,
although the degree of quality loss
depends just as much on the halftone
screen ruling you will use. To minimize
loss of quality when enlarging an image,
you must "resample up".
that you read our articles on
increasing your picture size.
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