What is Pixel Density and Pixels Per Inch ( PPI)?

  • by Rachel Hansen

To define the resolution of an image, the terms Dots Per Inch (DPI) and Pixels Per Inch (PPI) are widely used synonymously. The words do not mean the same thing, though, and that there are distinct variations between the two: DPI represents the number of printed dots that a printer prints within one inch of an image. PPI represents the number of pixels displayed on a computer screen in one inch of an image.

For a bunch of things, much of the misunderstanding occurs between these two words. First, even though PPI refers to the resolution of a digital on-screen image, the quality of the final printed image may also be affected. Second, even some specialist print services demand that before they can be printed, photos must be at a certain DPI level; what they typically mean is PPI, not DPI-so. This adds to the confusion.

A system for calculating the print size of an image on paper is the term DPI. Although some printer apps still use DPI, many newer printing applications have a setting instead so that you can choose exactly what size you want to print a picture at (5×7, 11×17, or other). Increasing the DPI will make the size of the printed image smaller for printing applications that use DPI for calculating the print size, thus decreasing the DPI will make the size of the printed image larger.

The performance of a digital image shown on-screen is represented by PPI. But, it also adds to an image’s consistency. If there are too few pixels in a digital image, the image won’t have much detail and will look pixelated. There is more clarity in digital images with more pixels. The sum of PPI is calculated by the photo’s image size.

What PPI Means

PPI, or pixels per inch, relates to both the fixed number of pixels that can be viewed on a screen and the pixel density within such a digital image. On the other hand, pixel count represents the number of pixels around the length and width of a digital image, i.e., the pixel image dimensions. The smaller building blocks of a digital image are pixels or ‘picture components.’ Zoom in to your picture, and you’ll see it broken into colored squares.

These are pixels. Within pixels, red, green, and blue light components are sub-pixels that can not be seen by the human eye since additive color processing combines them into a single hue that appears at the level of the pixel. This is why the RGB (red, green, and blue) color model, also called the additive color model, is used by PPI. Just in the electronic representation of images, such as television displays, computer monitors, and digital photographs, does this not occur in print.

What DPI Means

DPI, or dots per inch, is defined as a physical printer’s resolution value. By spitting out tiny dots, printers replicate an image, and the number of dots per inch determines the rate of detail and overall quality of the print. To monitor the amount of red, green, and blue light reflected from white paper, DPI uses the CMYK (cyan, magenta, yellow, and key/black) color model. This is also known as the model of subtractive color.