DPI / PPI

DPI (dots per inch) measures resolution, how many dots of detail are packed into each inch of an image or print. The higher the number, the finer the detail and the larger the file. It is the single setting that most often decides whether a scan or an export looks crisp or disappointing.

Different jobs want different numbers. Screen viewing is comfortable around 72 to 150 DPI, since a monitor cannot show more than its own pixels resolve. Quality printing wants about 300 DPI, the point at which dots blur into smooth tone to the eye. OCR is happiest at 300 DPI too, because the recognition engine needs enough pixels per character to tell letters apart, scan too low and accuracy collapses. Strictly, DPI refers to print and PPI to pixels on screen, though the terms are used interchangeably in everyday work.

DPI is also the main dial on file size: doubling it roughly quadruples the pixel count. When you export PDF pages to images or compress a document, picking a DPI that matches the destination, screen, print or OCR, is how you get the quality you need without a needlessly huge file, all computed on your own device.