Differences Between Offset Printing And Digital Printing

It is very much probable that you are not very aware of the present mode of printing techniques

. So it is high time that you learn a little about digital printing to keep yourself updated .

Offset printing involved a huge offset machine or a baby offset machine depending on the size of the paper to be printed. Baby offsets are used by small print shops for flyers and brochures in size A4 or A3 whereas large offset machines can print sizes 23 x 36 and even larger. The process involves preparing a plate which is a thin sheet of aluminum which is sensitized with a light sensitive lacquer. It is exposed with a film which bears the image, just like making a contact photographic print. The plate is then chemically processed and unexposed areas are washed out. The plate is mounted on the offset machine on a drum. As the drum rotates it comes in contact with rollers which are inking rollers which take up ink from ink wells. The inked plate transfers the ink to a rubber blanket and not direct to the paper. This is why it is known as offset printing. The rubber blanket transfers the image to the paper. For single color printing one plate was used. For multi-color, say 4 color, 4 plates were used, one for each color. Paper passes from one stage to the other till, at the end of the 4th stage (black, magenta, cyan, yellow) full color printed paper is ejected from the machine. Screens were used to break up the image into tiny dots. The plates have tiny dots which take up the ink and transfer it to paper. In each of the 4 plates, the dots are shifted and the composite color print is a collection of small colored dots which give the impression of full color to the eye depending on the fineness of the dots and spacing. Latter day techniques used more than 4 colors in offset printing for better vivid and saturated reproductions. Earlier machines were single color. To get full color reproductions plates were mounted one after the other and paper passed 4 times to get the final full color result. Disadvantages were lack of registration due to non-alignment and stretching of paper and slippages. Modern full 4 color presses employed four drums and paper passed from one to the other with electronic alignment to ensure perfect registration. High volumes were necessary to make the process cost effective.

Digital printing can be as simple as the inkjet printer attached to a computer at home. Data (in the form of bits and bytes) is transferred from computer to the inkjet or laser printer directly and printed using inks or toner or dye sublimated solid inks directly on the paper. Digital printing is also more complex with imaging systems such as Canon and Xerox systems which are capable of high volume printing at affordable costs. Data from the computer is transferred to such systems through a fiery print server which rasterizes the data (text and images) to a form the printer can understand and print fast and perfectly. Advantages of such systems are perfect reproductions and adjustable volumes. Cost is also low. Suppose a company is manufacturing machines with certain specs. It can get say 100 to 500 brochures printed at a low cost. If there are changes in the specs or models such changes can be made and another lot printed easily. For offset printing minimum print quantities would have to be 5000 and costs would be prohibitive.

by: Jovan Normandia

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