Prepare to print - the difference between dpi, ppi and lpi
DPI means *dots per inch*. In the days before artwork was prepared on computers, this term was quite common. People still use it today, but they shouldn't, it just confuses things. If you do, you show your ignorance of the process. So stop it. Don't say *dots per inch*.
PPI means *pixels per inch*. Ah, now you're sounding more intelligent! A pixel, which means *picture element*, is how images are broken up when they are scanned into a computer. They are those little square things. And how little, or how big, they are, is determined by how many can fit in an inch. The screen that you are looking at right now, on your Mac, is 72 pixels per inch. No, you really can't seem them, that's the whole point. They blend smoothly together, giving the illusion of continuous color. When you use Photoshop, you need to know what your ppi will be before you start. So, if you are preparing artwork that will only be seen on a computer, like a web page, your artwork needs to be 72 ppi.
LPI means *lines per inch*. This is used to describe the size of the dots (no, we don't say *dots*!) for publication. They are not lines, of course, it just means if you drew a line through the dots. And before you can begin preparing artwork for publication, you need to know the lpi of the publication. And, as a general rule, lpi is 300, 175, 150, 133, and 65. The higher the number, the more precise the printing press needs to be. Newspapers are low. Really, really, nice magazines are high. A word of warning here - there are a lot of old grouchy people who are still around that pre-date the digital era. If they say *dots per inch*, they mean lpi. Don't correct them, unless you want to start an argument.
The reason that you need to know all this stuff is that your artwork will look different once it's published than how it looks on your computer screen. If you miscalculate the ppi, and make it too low, then the artwork will look all blurry and *jaggy*. If you miscalculate the ppi, and make it too high, the files will bog down and take forever to load and rip (raster image process). Either way, you look like an idiot.
So here is how you do it -
Find out the lpi of the publication. Prepare your artwork to be twice lpi. So if the lpi is 150, the ppi should be 300. Yes, it's complicated - and all you have to be is perfect. But that's why you wanted to be a Graphic Designer, right?
Posted by Brad Hall