I’ve been working on some print design projects and keep coming across the terms DPI and PPI. I know they both relate to image resolution, but I’m a bit confused about the exact difference between the two and how they impact print quality. Can someone break down what DPI vs. PPI really means in the context of print design? Also, why does it matter so much when preparing files for print? I’d love to get some insights on when to use each and any tips for ensuring my designs look sharp and professional when printed.
People often use the terms interchangeably, but they’re very different things.
PPI (pixels per inch) refers to the resolution of a digital bitmapped image, such as a photo or a scanned illustration. These images are composed of rows of pixels. PPI refers to how many pixels per inch are in each row. For example, a 300ppi digital image will have 300 pixels in a one-inch row of pixels.
DPI (dots per inch) can refer to several things. The term usually refers to the number of ink dots on a printed page, but it can also refer to the resolution of a digital printing device.
In offset and letterpress printing, images are printed using small dots of ink called halftone dots. If there are 150 halftone dots in a one-inch row on a printed page, the resolution of those printed dots is 150 dpi. In this instance, the term LPI (lines per inch) is sometimes used, but you probably won’t run into that term outside an offset print shop.
In digital printing, halftone dots aren’t used. For example, in inkjet printing, tiny dots of ink are sprayed onto the paper (or other substrate). In laser printing, tiny dots of toner are fused to the paper. The number of these dots a printing device lays down is the DPI. The DPI of these devices can vary wildly from low resolutions of 60 DPI (on an old dot matrix printer) or less to thousands of DPI for high-quality printing devices (for example, an imagesetter).
Similar to the difference between typeface and font, technological advances have blurred the difference between PPI and DPI to the point where, for casual users, the terms seem almost synonymous, but in reality, they refer to related but distinctly different things. When you run across the term DPI being used, my guess is that 99 times out of a hundred, the term PPI should have been used instead.
Thanks buddy