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Just what is Digital Printing? Traditional printing is carried out using
printing plates on a printing press. These plates, made from very thin aluminium coated with a special light sensitive layer, carry the image
of the text or picture to be printed. The plates are mounted on a drum on a printing press and as the drum rotates the image on the plate picks up ink and transfers it (eventually) to the. For colour printing, the paper is printed four times - once each in cyan, magenta, yellow, and black.
The all important image on the printing plate is produced using a photographic process. The page to be printed, say a newspaper, is 'pasted up'
from smaller pieces of text and pictures and a large photo is taken of it. The resulting large negative film
- as big as the broadsheet newspaper - is used to produce the image on the light sensitive layer on the printing plate by shining a light through it (much as you might shine a light though a holiday snapshot slide). The pate is then
developed to wash off the residual light sensitive layer. However, this is all very different to the desk top printer you use with your computer. Desk top printing is digital, and digital printing
carried out by 'proper' printers is really just a souped up version of desk top printing. All computer data is digital
(the famous binary 1's and 0's) and all the text you might wish to print out of your word processor is in digital form. How does this happen? Imagine that this text you are reading was divided up into hundreds of horizontal lines. If you looked in minute detail at one individual line going across the page, it would either be ink or blank paper - there would be an image or no-image - 1's or 0's. So you could define the horizontal line as a series of 1's an 0's. Now, imagine peeling off, from the top of the page, each horizontal line to give a very long string of 1's and 0's. This is the
digital data, which can now be printed. This string of unravelled data is fed into a digital printer, which reassembles the lines from the 1's and 0's onto the paper to be printed. Imagine the string of
data being pasted, from top to bottom from left to right, onto a new sheet clean paper - 1's/0's, image/no-image, ink/no-ink. That is digital printing. The ink dots that corresponds to the 1's can
be placed onto the paper in various ways. Ink jet technology for example sprays tiny dots of ink, across the page and back again (a raster scan), to match up with the 1's (and 0's) in the stream of digital
data. It is possible to do all four colours at once, each new colour being printed one line behind the first colour. Laser printing, rather than putting the ink dots onto the paper, 'writes' the lines of dots
across a special sensitive drum, which then picks up toner on the spots corresponding to 1s, and then transfers this onto the paper. Traditional printing reproduces the image by photography and stores the
image on film whereas digital printing produces and stores the image electronically in a computer. Traditional printing prints whole pages at a time using a printing plate and can produce thousands of copies of the same
image very quickly, whereas digital printing 'writes' the image in a series of rows of dots down the page and can even send a different stream of data to the printer to produce a different image each time. Digital data
can also be transmitted, perfectly, to print the same image, anywhere, anytime. |
