An Overview of Digital Printing Systems - Control of Color Imaging Systems: Analysis and Design - page 14

color management software, multimedia handling software (speech to text conversion)
are used heavily. Pre ight is a final checklist to ensure that the files are ready for

printing. Failure to prepare all digital files can cause delays and cost overruns.

Scanners and digital cameras usually capture color images in RGB type format,

where each channel is quantized to 8 b pixel. They can also act as sensors to perform

color analysis of the image. They are de

=

ned in an 8 bit three-dimensional (3-D)
color space whose components are red, green, and blue ( RGB ). One typical function

of the color management module would be to correct compensate for scanner or

camera artifacts with respect to the tone reproduction by calibrating and character-
izing the devices and further compensating for device differences. Generally speak-
ing, two different scanners imaging the same spot in a hardcopy will generate
different RGB values. As a result, the color management module needs to transform
the color from a device-dependent space (a speci

=

c scanner RGB ) to a device-

independent space (L*a*b* or independent ) to ensure quality color reproduc-

tion. The transformation usually is in the form of a multidimensional LUT, which
is generated by measuring known color targets for sample of colors [16

RGB

-

20]. Any
color that falls between is interpolated using a standard technique like trilinear or
tetrahedral interpolation. Image processing techniques like denoising, deblurring,
up cation, are

applied to the image or video frame as dictated by the user prior to its inclusion in a
given document [3].
In an ideal preferred print work

= down sampling, cropping, color manipulations, and histogram modi

ow, the prepress environment would incorporate
an accurate color model of the production environment within the design tool, which in
turn helps to view the color images on a calibrated monitor (soft proo

ng) or a proofer

(hard proo ng). The design inspection involves looking for image quality defects (e.g.,

the loss of shadow or chromatic details, color balance, contours, smoothness, etc.)
prior to running production jobs. This process requires accurate characterization and
calibration of the monitors prior to viewing images so that the soft-proofed images
match the actual prints. A good test image is useful for evaluating monitor

is quality
and calibration as well as the match between the monitor and printer. For viewing
images, the multidimensional LUTs are used to transform the

'

first to a device-
independent color space and then on to the monitor color space. These transformations
have to be accurate and should not induce unnecessary image artifacts.
Thus, in this stage, the control functions are discretely handled at a lower
timescale based on capturing the model of the imaging system and processing
images with a myriad of algorithms. In recent years, image processing has become
more sophisticated and more prevalent in the digital print production industry.
Chapter 2 contains relevant theoretical fundamentals of important digital image
processing topics such as image formation, image sampling, quantization,

le

filtering,
transforms, denoising, resizing, etc. To help the reader understand how to extract
spatial frequency-based models, we also introduce the optical transfer function
and modulation transfer function of imaging systems. These models can be incorp-
orated in the printing work ow of the production environment. The spatial

models could help to perform diagnostics and design inspection for production
anomalies. Material covered in Chapter 2 is also helpful for processing images in
the DFEs.