If you make graphic displays or read a lot of web comics, you’ve probably seen these terms while using applications like Photoshop. While PPI and DPI may sound interchangeable, they actually aren’t. I’ll break it down in layman’s terms so next time you’re shopping for a printer or sending something over for publication you can sound like a multimedia boss and understand what’s going on!
PPI = Pixels/Inch
PPI has to be your primary focus when you start your illustrations because it determines the printing and display resolution. Most computer monitors and web renderings tend to use between 72 and 96 PPI thus why 72 is the default on Photoshop. However, mobile phones and tablets are where we get most of our information and they can render as high as 400 PPI. If you keep your work as 72 PPI, it would look fine on computer screens but not so much on high definition devices and it will pixelate easily when it’s blown up. An easy fix is when you’re creating a file, make sure you set your resolution to 300 or 400 PPI. It won’t change the file size and your work will look great no matter what format you decide to display it in. It’s best to set it up from the get-go. But in case you realize it afterwards, in Photoshop go under Image > Image Size and then you can change your resolution. Problem solved! 🙂
DPI = Dots/Inch
DPI is an aspect you can’t control. It describes the number of dots (usually RGB or CMYK) your printer/scanner can render within an inch and it varies widely. Printing is like clothing – different brands will deliver different results. What would look average in one printer can look amazing in another printer and they may not have the same DPI. DPI is good to know if you’re into printing graphics but in a layman’s usage it’s not very big of a deal. The reason why DPI and PPI often get mixed up is the result of Apple & Adobe advertisements misusing the term in the 1990s (which has been corrected since). So if you come across articles & blog posts describing DPI and they’re not discussing it in terms of printing or scanning, they’re most likely referencing PPI. How do you tell the difference? PPI is a fixed unit but can cover a limitless number of pixels (thus why we can render so high) whereas DPI can vary widely in size but there are physical limits when it comes to the number of dots they can render (thus why they tend to be in the 100s).
Digicam Guides and 99Designs did in-depth posts about the difference between PPI and DPI. If you’re more visually and metaphorically inclined like myself, Make Webcomics (Tapastic) did a witty strip on this topic. 😉