DIGITAL AND PRINT OUTPUT

Digital And Print Output

[Writer's University]Digital And Print Output

Q1: Why are there discrepancies between the image on the monitor and the same image as a printout?

The whole problem is the difference between what resolution your monitor displays and what your eyes are capable of distinguishing, as well as how the monitor handles picture information compared to how the printer handles picture information.  Ultimately it comes down to the number of dots (pixels) that your picture has, and how your eye blurs dots that are really close together.  Your computer monitor can only display between about 72-100 dots of information in every inch of screen (72-100dpi) depending on the screen resolution you have chosen in the control panel.  Once you select it, that is literally the number of dots your screen has in every inch, so it can do no better.  This does not mean that you cannot look at pictures that are higher resolution, but the monitor distorts the image in order to do so.  I have a 17" monitor set to 1152x864 (1152dotsx864dots) which equals a display resolution of about 90dpi, so I will use this in my explanations.  On the other hand print quality all depends on your eyes' ability to distinguish between denser and denser groupings of dots on a page.  In order to get non jagged edges on pictures you print, you have to print out at a dense enough grouping of dots that your eyes blur together the difference between them.  It turns out that your eyes blur together anything greater than a certain number of dots per inch (dpi), depending on your distance from the image, and the quality of your vision.  I wrote a page on the limits of your vision and how that relates to digital images as well.  You should probably read that section  before continuing on with this section.  Print quality images should be created at at least 175dpi at the absolute minimum and preferably at least 300dpi.  If you want really really clean quality printing that ensures absolutely smooth edges, 600 dots of information in every inch will absolutely guarantee a great print out.  However most printers do not print out at this quality, especially ink jets, and some laser printers do not either.  I happen to have an HP Laserjet 1100A that allows me to select between 300dpi and 600dpi printing, the tradeoff for selecting 600dpi is that the printing is slower than with 300dpi (Berns, 2000).

Q2: Why do we need to know both color systems?

So, now that you know how your eyes and the monitor works, here is why good quality print images appear huge on a monitor and pictures that appear good on a monitor typically print off with jagged edges.  For example, I will use an image I created for printing that I defined as 600dpi 6" wide by 3.42" tall.  At 600dpi, 6"=3600 dots (6x600) and 3.42"=2050 dots.  My computer monitor only displays 90 dots in every inch but interprets picture ...