Adobe PHOTOSHOP 5.0 User Manual page 61

2 Multiply the result in step 1 by the ratio of final
image dimensions to original dimensions to
determine an estimated scan resolution.
For example, suppose you are scanning a 2-inch-
by-3-inch image and want to produce a final
6-inch-by-9-inch image. You are using a screen
frequency of 85 lpi.
First multiply 85 (the screen frequency) by 2 to get
170. Then multiply 170 by 3 (the ratio of final
image dimensions to original ones) to get a scan
resolution of 510 ppi.
Different color separation procedures might
require different ratios of image resolution to
screen frequency (see page 45). It's a good idea to
check with your service provider or print shop
before you scan the image.
Scanning using the file size setting
You can create a dummy file to predict the file size
needed for the final output of your scan.
To calculate the file size before scanning an image:
Open Adobe Photoshop, and choose
1
File > New.
2 Enter the width, height, and resolution for your
final printed image. The resolution should be 1.5
to 2 times the screen frequency you will use to
print. Make sure that the mode you plan to scan in
is selected. (See "Color modes and models" on
page 63.) The New dialog box then displays the
file size.
For example, suppose you want the final image to
be 4 inches wide and 5 inches high. You plan to
print it with a 150-line screen using a 2:1 ratio, so
you set the resolution to 300. The resulting file size
is 5.15 megabytes.
To produce the scan, enter the resulting file size in
your scanner settings. Don't worry about
resolution or image dimensions. After you have
scanned the image and imported it into
Photoshop, use the Image Size command to enter
the correct width and height for the image.
Optimizing the dynamic range of the scan
Keep in mind that the human eye can detect a
wider tonal range than can be printed. If your
scanner allows, set the black and white points
before scanning a file to produce the best tonal
range and capture the widest dynamic range. Then
use Photoshop's color correction tools to set the
white and black points for the scanned image (see
"Step 3: Set the highlight and shadow values" on
page 114).
Eliminating unwanted color casts
If your scanned image contains an unwanted color
cast, you can perform a simple test to determine
whether the cast was introduced by your scanner.
If it was, you can use the same test file to create a
color-cast correction for all images scanned with
the scanner.
ADOBE PHOTOSHOP 5.0 53
User Guide