Printing Resolution Revealed

DPI – The factor governing the quality of images reproduced by modern printing devices

The final result of any print obtained using a modern printer, whether of the offset, laser, dot matrix or some other type, would depend on the dpi of the printed image. The term 'dpi' or dots per inch is one that is of misconstrued or misunderstood and is mostly confused with the term 'ppi' or pixels per inch. Before embarking on any further deliberation, it is essential to understand the general difference between the two.

DPI relates to the resolution of a printed image, whereas PPI refers to the unit of measurement related to the resolution of a computer display. In case of an image scanner, DPI would refer to the scanner's capability to scan within a given range or for a printer, denote the range of resolution supported by a printer for printing images. Dots per inch, as a measure of printing resolution, denote the number of dots of ink that a printer produces within a linear space of one inch. Broadly speaking, the higher the dpi, the better the resulting image.

For a printed reproduction of an image that is qualitatively comparable to its video graphic counterpart as displayed on the computer screen, the dpi of the print needs to be much higher than the ppi of the video image. A single pixel in a video image would normally require four to six dots of ink to be represented in print. Hence, an image that is 100 pixels wide would require four hindered to six hindered dots in the printed version. For a 100 x 100 pixel image to be accurately reproduced in a 1 x 1 inch print, the printer should be able to print at 400 to 600 dots per inch.

Successive technological improvements have resulted in bettering the quality of printing and excellent prints can now be accessed through various equipment. However, all this still remains quite confusing for a novice and one not technically savvy. The success or the final outcome is dependant on the selection of compatible software and hardware, consisting of the video camera, processor, scanner and printer.

Printer types:

Dot matrix printers: The dot matrix printer is a type of impact matrix computer printer that creates prints by impact, i.e. striking a color impregnated ribbon against the paper through tiny pins or rods operated electromagnetically. For accuracy, these minuscule pins operate through a guide plate made of sapphire. These printers are sturdy and still in use today for carbon copy printing and multipart stationery. With dpi improved from 60 to 240, the use of these printers is rather limited on account of loud noise, low speed, low-resolution graphics and limited color performance.

Inkjet printers: Inkjet printers are of three types.

(a) Thermal Inkjet printers use a water-based ink and an electrical current is passed in a heating element to form a bubble of steam, to push a tiny droplet of ink onto the paper and hence it is also called the 'bubblejet' printer.
(b) Piezoelectric inkjet printers use piezoelectric material in place of a heating element.
(c) Continuous inkjet printer use a technology that makes a high pressure pump deliver liquid ink in a regular stream in a gun-body, where it is broken into 64000 to 165000 drops per second through an acoustic wave generated by electrically vibrating piezoelectric crystals.

Laser printers: Laser printers have the flexibility of a wide variation in operating speed with the upper end models being able to print over 200 monochrome pages every minute. Color laser printers are capable of printing over 100 pages per minute, which translates to six thousand pages per hour. Laser printers are capable of delivering anywhere from 600 to 1800 dpi. Their method is to apply toner through a controlled electrostatic charge.

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