DPI vs PPI
Also known as: dots per inch, pixels per inch, image resolution for print, dpi meaning
DPI (dots per inch) describes how many ink dots a printer lays down per inch, while PPI (pixels per inch) describes how many pixels fit in an inch of a digital image or screen. DPI is a print measurement; PPI is a screen and source-image measurement, and the two are often used interchangeably but mean different things.
- PPI = pixel density of image or screen
- DPI = ink-dot density of a printer
- The stored value is metadata, not extra detail
Print vs screen
PPI belongs to the digital world. It is the pixel density of an image or a display — a 1000-pixel-wide image printed at 250 PPI becomes 4 inches wide. On screen, the pixel count is what matters, so a "DPI" setting saved in an image file changes nothing about how it looks on a monitor.
DPI belongs to the printer. It is how finely the hardware can place ink dots, and a single image pixel may be reproduced by many printer dots. You raise effective print quality by sending enough pixels for the size you want, not by editing a number in the file.
What actually controls quality
For a sharp print, what counts is the pixel dimensions of the source image relative to the physical size. Most photo printing aims for a high pixel density at the final size; enlarging a small image to fill a big print spreads the same pixels thinner and softens detail.
The DPI/PPI value stored in a file is just metadata — a hint to print software about default size. It does not add or remove pixels, so changing it alone never improves real resolution.