Printing Part 1

I joined my job in June 2006 at Adobe India. The very first day, I was told that I was part of the PostScript team. Now, someone joining Adobe expects to work on a product the entire world knows about. I had heard of PostScript, and for me, all it was was a free legal way of generating PDF Files. Apart from that, I had no idea what it did.

I was always fascinated with PDF's too, they looked so cool on the screen! I never really considered them to be anything but a really convenient method of exchanging neat looking documents that can be printed nicely. So, what do PS and PDF have to do with the printing industry? (They must have something to do with it, because that's what the title says!) Ok, let me digress a little more. I'm sue all of us have seen a presentation on how a printer works. The entire mechanism, the rollers, the ink roller, the laser beams, the works. We also know that the laser beam hits the points where a dot is supposed to be placed, and the ink then sticks to that dot on the roller and eventually to the paper, where it is heated and 'printed'. Neat isn't it. Now, just out of inquisitiveness, how does the printer know what dot to mark and what not to mark?

It never struck me that it would be impossible to actually send the Rasterised and halftoned images to the printer to print! You never think of these things do you. I'll tell you why. Lets take a 4 color laser printer (CMYK), capable of 1200 dpi, and a conservative page size of 11"x8". Thats 88 square inches x 1200 = 105600 dots per color. Now there are 4 colours, so x 4 = 422400. Well, that calculation assumes that the printer can either place a dot of ink, or no dot of ink. It has no control over the amount of ink it can place. In other words, what is the bit depth of the printer? Low end printers would be 1 bit, high end would be 8 bit. Lets just assume that we have a 8 bit printer. That means 8 bits of data for each colorant sample. Again, 422400 = 3379200. That many bits of data per page! Lets get that into familiar units. 3379200 / 1024*1024 = 3.22 MB.

3.22 MB data to print one single sheet of paper! It may not sound like much, but think of a network printer catering to 100 people. Let alone that, if you want to print a 200 page document from your computer in 4 color, you need to transmit over 600 MB data! Thats not possible is it? That obviously does not happen! Well, in some kinds of printers, called GDI printers, it does happen that way. More flexible printers though, use page definition languages such as PostScript and PCL, which are vector capable languages, and the rasterization of these vectors is don on the printer itself. So now, you can actually specify or embed the font into the PS, specify the size and placement of the glyphs, and send a tiny file to the printer.

In this series of blog posts, of which this is the first, I will take you through some of the basics of printing, and all the related stuff. Stay tuned..

As a time-pass, if you really are interested, I recommend this :
Download 'Digital Editions' from labs.adobe.com. In the sample e-book library, you will find a book called 'Inside the Publishing Revolution : The Adobe Story'. Read that. Start Here.

Labels: Print