Digital Imaging Tutorial - Quality Control
the X chromosome. Since females have two X chromosomes and males have
one, the chance of color-deficient vision is 1 in 250 females, but 1 in 12 for
males. Even among expert viewers, differences in judgments due to normal
variation in the human eye are not uncommon. A
color vision test can be used
to evaluate a viewer's vision.
Images may appear different on different monitors. Calibration is the process
of adjusting monitor color-conversion settings to a standard, so that the image
displays the same on a variety of monitors. The ideal method is to use
monitor-calibration hardware and accompanying software. However, if you do
not have access to these resources, use your application program's
calibration tools. For example, Adobe Photoshop includes a basic monitor-
calibration tool, which can be used to eliminate color cast and standardize the
display of images.
One of the main challenges in digitizing color documents is to maintain color
appearance and consistency across the digitization chain, including scanning,
displaying, and printing. Accurately reproducing colors is difficult because
input and output devices treat colors differently. The goal of color
management system (CMS) software is to ensure that the colors of the
original match as precisely as possible the digital reproduction on-screen or
6. Evaluate System Performance
Whether conversion takes place in-house or is outsourced, system
performance should be evaluated to ensure consistency throughout the
conversion process. Among characteristics to evaluate are resolution,
linearity, flare, scanner noise, color reproduction, and various artifacts.
Several publications noted at the end of this section provide further
information on system calibration.
7. Codify Your Inspection Procedures
Quality control data has long-term value, from supporting different stages of
quality inspection to facilitating future manipulation and migration. For in-
house components of QC, we recommend detailing the inspection procedures
in a short manual (or in a series of workforms) to be used in training and to
facilitate workflow. Issues that need to be addressed include: QC procedures;
staff involved and skills needed; instruments, hardware, and software needs;
rejecting and replacing unacceptable products. An example of this approach
is demonstrated by the Library of Congress in its
Internal Training Guide.
You retrieve an image from a CD that just arrived from the
image production unit. The image is not crisp and looks darker
than what you had expected. What is the first thing to do to
determine the cause of the problem?
(A) Confirm that your viewing environment is correct.
(B) Use the adjustment tools (sharpening, color correction)
available in your image viewing software to bring the image in
line with expectations.
(C) Call the image production unit to find out what
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