Dots per inch

Comment by Kris Zaklika of Jasc's Paint Shop Pro fame

> You are right, of course, but aside from magazines (which apparantly are so
> dumb that you can redefine their submission specs on the fly, or is *that*
> why you aren't getting lo's printed? oh my!) printing companies, by a vast
> majority, require files of 300 dpi for printing.

This has to do with the nature of offset printing and paradoxically relates to the lower quality of offset printing compared to printing on an inkjet. A magazine is printed with a 150 line per inch screen, which determines the spacing of individual cyan, magenta, yellow and black dots on the paper. To allow proper sampling of the image and creation of 150 dots per inch, your image must have 300 pixels per inch, i.e. information at twice the rate at which you intend to
sample it. (Look up "Nyquist frequency" if you want to learn more.)

However, in an inkjet printer each pixel is represented by many dots of ink, perhaps as many as 64. The inkjet therefore gives you better quality in two ways: (1) more pixels per inch (200 vs around 150) and better pixel color (64 dots of 4 to 6 inks, possibly with variable-size drops, versus a single dot of one of 4 inks, albeit with a dot that fills from 5 to 95% of a line screen grid square).

In other words, more of the original image information is lost in offset printing than in inkjet printing. As a result, there are no hard and fast rules without taking into account the nature of the printing process. This makes it pretty confusing if you are new to the business of graphics. However, the vast majority of newcomers will not be preparing their work for offset printing so 300 ppi is overkill for them. It seems like more must always be better but, because of technicalities and fundamental limits created by the properties of your eye, this is not always the case. Your point that humanity as a whole may be ineducable on this topic may well be true but it doesn't stop some of us trying :)

[snip]

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