This article is somewhat technical – you may first want to read What is a Pixel?

Resolution is a word that is being thrown about and used in many ways while discussing monitors, printers and digital cameras. Thus, there is a lot of confusion about resolution.

Most references to resolution are in the form of dots per inch or pixels per inch. Thus, there is a physical measurement involved. If it has a resolution of so many pixels or dots per inch this means that the image is being observed on a monitor or a printed sheet of paper. Something physical.

Printer Resolution (dots per inch): An inkjet printer creates the printed image using very tiny dots of ink that are ejected from the print head. On the common 3-color (+ black ink) printer, each dot is one of the following colors: Cyan, Magenta, Yellow, Black (called CMYK). There is usually a separate black-ink print head cartridge. The print head is a physical thing, so it does have a fixed resolution of dots per inch in the vertical dimension. The holes are spaced physically above and below each other. The print-head moves horizontally across the paper and the ink is ejected by timing. This means that the horizontal resolution varies (actually depends on print quality selected). See simplified print head below.

Monitor Resolution (pixels per inch): A common resolution that is stated for monitors is 72 pixels per inch.
This is not strictly correct. Monitors are different sizes (14-inch, 21-inch…) so the same image will have different inch measurements on different monitors. If the monitor resolution is set for 800 x 600, an 800-pixel wide image will fill the screen! But if the monitor is set for 1024 x 768 (a common setting), that same 800-pixel wide image will not fill the screen. So we don’t have a specific physical resolution. This is not an effort to confuse you, but rather to emphasize that the term resolution is used in several ways. It may save you a headache to know this. J

Digital Camera Resolution (megapixels): Sometimes, the term resolution is used for a simple quantity of pixels, independent of physical measurement (inches are not mentioned). One could say: "If you are going to print, set the camera to a high resolution." Thus, the photographer would set the camera to produce an image with a large number of pixels or megapixels (millions of pixels).

The image in a digital camera originates as data on a tiny optical sensor. For example, 3 million pixels are stashed on a sensor chip that is only ¼ inch square! What is the resolution? The answer is that there is no physical resolution in pixels per inch. There is only a quantity of pixels or megapixels. When the image data finally reaches the outside world printed on paper, this translates to dots per inch.

© 2004 Fred Hall