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72
Adobe Photoshop Help
Getting Images into Photoshop and ImageReady
Using Help
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Contents
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Index
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72
Scanning using the file size setting (Photoshop)
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:
1
In Photoshop choose 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. For more information, see
“About color modes and
models (Photoshop)” on page 86
. The New dialog box 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 MB.
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 (with the Resample Image option
deselected) to enter the correct width and height for the image.
Optimizing the dynamic range of the scan (Photoshop)
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
adjustment tools to set the white and black points for the scanned image. (See
“3. Adjust
the tonal range.” on page 129
.)
Eliminating unwanted color casts (Photoshop)
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.
To identify and correct a color cast introduced by a scanner:
1
Make sure that your monitor has been calibrated. (See
“Creating an ICC monitor profile”
on page 117
.)
2
Open a new Photoshop file, and use the linear gradient tool
to create a blend from
pure black to pure white.
3
Choose Image > Adjust > Posterize, and posterize the blend using 11 levels.
4
Print the 11-step gray wedge on a black-and-white printer, and then scan it into
Photoshop.
Note:
You can also perform this test using an 18-percent neutral gray card or an 11-step
gray wedge from a photography store.
5
Open the Info palette, and read the RGB values on-screen for each of the gray levels.
Uneven R, G, and B values indicate a color cast.
6
Use Levels or Curves to correct the color cast, and then save the dialog box settings.
(See
“4. Adjust the color balance.” on page 130
.)
7
Open the scanned image you want to correct, reopen the dialog box you used to
correct the cast in step 6, and load the saved settings.
