DPI (dots per inch) and PPI (pixels per inch) both describe the resolution of an image. If you have an inch, the DPI or PPI is how many dots or pixels are in that space.
DPI vs. PPI, Is There a Difference?
Historically, people used PPI to talk about digital pieces and DPI to reference printing. In today’s world, people use both terms interchangeably. They both convey the number of pixels in a given image.
What’s the Best DPI for Digital Screens?
Since DPI refers to the density of pixels within a given space, an image with a low DPI will look grainy compared to one with a high DPI. If you’re designing for a digital display, you’ll want to set the DPI to 72. This size is the maximum pixel density of most computer monitors.
While most of your designs will only need 72 DPI to show up clearly on most screens, there are exceptions to the rule. Some 4k monitors, e-readers, and other specialty displays require 300 or 400 DPI.
What’s the Best DPI for Print?
You never want to go below 300 DPI for print because your collateral will become blurry. You’ll want to ask your printer what the best DPI is for your printing needs. Typically, you won’t need to print above 450 DPI unless you’re printing for a large billboard or banner.
Beware of Large Print Files!
Images above 450 DPI won’t appear crisper in a normal-sized document, but they will eat up your file space. In InDesign, you’ll want to set PDFs to trim down files over 450 DPI to save on file space.
Effective DPI in InDesign
InDesign also has a unique tool called effective DPI. Say you have an image that is 1,000 pixels x 1,000 pixels at 100 DPI. If you shrink it to 1/3 of the original image size (333×333), your image will go from 100 DPI to 300 DPI. In short, making the image smaller will increase its DPI.
How to Keep Your DPI In-Check With InDesign
Let’s say you are creating a newsletter for a non-profit. On the back of it, you need to include a list of all the board of directors. Each board member has an ultra-high-resolution portrait photo of around 20 MB. However, each portrait only needs to be the size of a postage stamp.
While the images started at 300 DPI, they may become 1,000 to 2,000 DPI as you make them smaller. Since these images are small and you don’t need the high resolution, set InDesign to drop the resolution of your photos to 300 DPI automatically from the “Save PDF” dialogue. This setting will help you save a ton of file storage space. While designing, you can always check the “Effective PPI” from the links panel (window > links).