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Scanning Black & White
images in Adobe Photoshop
STEP 1: Test and Compensate for the Scanner
This process requires a 12-step printers' grayscale.
You can get one through one of the resources below
or through a local graphics arts company or art store.
- Scan the 12-step grayscale
First, scan the grayscale. Once the scale appears on your screen,
choose the Show Info command from the Window pull-down menu.
- Read Highlight and Shadow
Position Photoshop's Eye Dropper tool over steps 1, 3, 6, 9,
and 12 of the grayscale (noting the readings of each step in the info window).
The info palette should show readings of 0, 25, 50, 75, and 100%, respectively.
If your scanner does not read these gray values correctly, a curve may need
to be created to achieve the correct tonal values.
- Creating a Curve to Compensate for Scanner
To create a curve, choose the (Adjust->Curves) command
from the Image menu. A new window with a curve will appear. At the bottom
right of the curve you will notice the Input and Output information displays
(Item #1 below). Click once on the grayscale at the bottom of the
curve window (Item #2 below). This will change gray level readings
to a percentage. (Note: if after clicking there your readings do not
show a "%" symbol, you should click again. Your readings should
have a "%" symbol.) Adjust the curve so that the steps on the scanned
grayscale read 0, 25, 50, 75, and 100% at 1, 3, 6, 9, and 12, respectively.
Then save this curve as Grayscale Curve in an easy access location.
This curve can be applied to all scans to compensate for the scanner's deficiencies.
This curve is designed as a general compensation to provide good
quality scans from your personal scanner. The curve should be applied to
all scanned images as a compensatory measure.
- Loading a Curve
To load a Curve you previously saved. Scan or open an image and
open the curve window (Image>Adjust>Curves..). Then choose Load...
and navigate to the curve you previously saved. The curve will then be applied
to the image.
STEP 2: Compensating for Press Conditions
- Analyzing Highlight and Shadow Dot Percentages
The grayscale curve can be modified to compensate for press conditions,
maximum and minimum dot, and dot gain to reflect the press requirements.
To determine if any additional adjustments need to be applied to your image,
first open the Info palette. Next, use Photoshop's Eye Dropper tool
to read the image's lightest and darkest points.
The highlight dot, the lightest
area of the image, should not be less than a 4%
dot, shown below on left.
The shadow dot, the darkest
area of the image, should not be darker than a 94%
dot, shown below on right. If your highlight and shadow values
are outside those ranges, you will need to adjust the image.
(To access the curve palette, select Image->Adjust
from the pull-down menu and select Curves. The curve window will appear.)
Select the point at the lowest end of the curve (the highlight
dot). Upon moving the dot, you will notice that the values in the Input
and Output will begin changing. The value should increase by the amount
of the difference between your smallest percentage and 4%. For example, if
you read a highlight value of 1%, you will need to click on the lower left
side of the slider, and move it so that the Input value reads 0%,
and the Output value reads 3%. (Thereby changing a 1% value to 4%.) Do the
same for the shadow dot, moving the 100% Input value so that the Output decreases
by the amount of the difference between your highest percentage and 94%.
Adjusting the Highlights (below)
Adjusting the Shadows (below)
Adjusting the Midtone (below)
The midtone range can also be adjusted if needed. This
can be done by selecting the middle of the curve (see below). The Input and
Output values should read 50% and 40%, respectively. Be careful when adjusting
the midtone dot; too much or too little adjustment can easily degrade the
quality of the image. Generally it is better to slightly adjust the image
than it is to over adjust it.
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