This section covers the main elements of current digital printing technology. It should be noted that this does not include presses where the printing plate is imaged on the press (computer-to-press), only those machines capable of changing successive images.
Currently the majority of digital presses rely on electrostatic methods of imaging. This is very similar to the way that a photocopier or laser printer works. An image is painted on to a uniformly charged photosensitive drum using a laser(s) or Light Emitting Diodes (LED's).
The light from the laser or LED hits the drum and dissipates the electrical charge, creating a latent image (ink attracting). The drum continues to rotate through a trough containing the toner (ink) and developer. The toner is attracted to the latent image, but not the white areas.
As the drum revolves the ink is transferred to the surface of the paper using electrical charges. The drum continues to revolve and is electrically cleaned to remove the image from the previous exposure. As each time the drum revolves and entirely new image is created, it is possible for each successive print to be different from the last.
In general, for four colour work, the process is repeated four times for the four process colours yellow, magenta, cyan and black. In the illustration above the paper is fed into the IBM InfoColor 70 from the large roll within the paper supply. The paper is conditioned using heated rollers to create the correct moisture content. It then passes through the developer units. There are eight developer units in all, four for each side of the paper. These image the main process colours (yellow, magenta, cyan and black).
When the image has been printed in all four colours, it is fused onto the paper at high temperatures. The paper with the fused image is then cooled and cut to the required page length. Printed sheets are stacked in the receive unit.
Saturday, September 19, 2009
Digital Image Processing
Many of the techniques of digital image processing, or digital picture processing as it was often called, were developed in the 1960s at the Jet Propulsion Laboratory, MIT, Bell Labs, University of Maryland, and a few other places, with application to satellite imagery, wirephoto standards conversion, medical imaging, videophone, character recognition, and photo enhancement.[1] But the cost of processing was fairly high with the computing equipment of that era. In the 1970s, digital image processing proliferated, when cheaper computers and dedicated hardware became available. Images could then be processed in real time, for some dedicated problems such as television standards conversion. As general-purpose computers became faster, they started to take over the role of dedicated hardware for all but the most specialized and compute-intensive operations.
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subfield of digital signal processing, digital image processing has many advantages over analog image processing; it allows a much wider range of algorithms to be applied to the input data, and can avoid problems such as the build-up of noise and signal distortion during processing.
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subfield of digital signal processing, digital image processing has many advantages over analog image processing; it allows a much wider range of algorithms to be applied to the input data, and can avoid problems such as the build-up of noise and signal distortion during processing.
Digital Printing
Digital printing is the reproduction of digital images on a physical surface. It is generally used for short print runs, and for the customization of print media.
The process differs from lithography, flexography, gravure, and letterpress printing in several ways:
* Every print can be different, because printing plates are not required, as in traditional methods.
* There is less wasted chemical and paper, because there is no need to bring the image "up to colour" and check for registration and position.
* The ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface and may in some systems be additionally adhered to the substrate by using a fuser fluid with heat process (toner) or UV curing process (ink).
Because there is less initial setup, it is useful for rapid prototyping, and cost effective for small print runs.
Digital Printing is used for personalized printing, or variable data printing (VDP or VI), for example personalized children's books, which are customized with the specific child's name and images. Print on Demand (POD) systems also use digital printing, for short run books of varying page quantities, and binding techniques.
The process differs from lithography, flexography, gravure, and letterpress printing in several ways:
* Every print can be different, because printing plates are not required, as in traditional methods.
* There is less wasted chemical and paper, because there is no need to bring the image "up to colour" and check for registration and position.
* The ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface and may in some systems be additionally adhered to the substrate by using a fuser fluid with heat process (toner) or UV curing process (ink).
Because there is less initial setup, it is useful for rapid prototyping, and cost effective for small print runs.
Digital Printing is used for personalized printing, or variable data printing (VDP or VI), for example personalized children's books, which are customized with the specific child's name and images. Print on Demand (POD) systems also use digital printing, for short run books of varying page quantities, and binding techniques.
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