Computer Screen Images versus Print Images

by Paul Jacobsen

This overview article is intended to familiarize you with some differences between the quality you see on a computer screen and that which you see when you print those images. Often people are surprised at less than acceptable results on paper when an image looked crisp and vibrant on the screen.

There are two principle factors to understand - palettes and resolution. Looking at palettes first, the difference between the two is that computer monitors use the 'RGB' color generation method (similar to a TV) wherein colors are made by combining R-red,
G-green and B-blue. The range of colors possible by combining those three in every manner possible is called the 'RGB palette'. Subtle variations are created by adjusting the intensity of the colored light beamed at each 'pixel' (remember that word) on the screen, resulting in a palette of some 16 million colors!

Conversely, a printer uses what is called the 'CMYK palette'. Now we are dealing with a device that uses four distinct colors to produce its palette ... C-Cyan, M-Magenta, Y-Yellow and K-Black. Droplets of ink are combined in each 'print dot' (remember that term too because it relates to pixels) on the paper to produce the final image.

With the foregoing in mind, the first difference you will see when printing an R-G-B computer image to paper is a color shift which is most often disappointing. The reason for this is simply that the computer and printer are struggling to make a three-color image into a four-color image.

The second obvious difference you will note (often to your disappointment) is that the nice image you just printed from your computer screen looks rough and fuzzy when committed to paper. This is due to "resolution", which is the number of pixels or print dots to the square inch.

A computer 'pixel' is to your screen what a 'print dot' is to a piece of paper. Most computer monitors function with between 72 and 96 pixels per square inch of screen, which means the image you see in the screen is made up of between 5184 (72 x 72) and 9216 (96 x 96) per square inch on the screen.

Generally printers begin at 300 print dots per square inch (standard) and go to 1,200 on high-end machines used by consumers. This means that printed images are made up of between 90,000 and 1,440,000 print dots per square inch. Without even using your calculator it is clear that the clarity of an image will be much different printed at 5184 print dots per square inch (a typical website image) than one which is printed at 5184 because it was generated originally for print use. Commercial applications deal with resolutions of 2,400 and up!

You may now say; Why not use the higher resolution images on the screen? There are two parts to the answer. One is that the 300 dot-per-inch image that is small on paper would be huge on the screen ...but most importantly is the file-size of each and because the file size of a print image is so much larger, the download time from a website to your computer would be significantly increased and overall the internet would be a much slower moving place!