Determining Lines, Inches, and Pixels

If we are aware of the size, density, and number of pixels on a sensor and recognize the other variables to a camera's resolution, are we better able to determine the quality of the images a camera can produce? The answer is a resounding no. Pixels are the units of measurement relating to the camera's resolution only, not the image resolution.

Raw camera resolution is shown in pixels, but image resolution is referred to in ppi, or pixels per inch; that is the number of pixels for every square inch of the photo. A 300 ppi image means there are 300 pixels on each square inch of the image.

Because sensors that are the same size can have a different number of pixels, measuring on the ppi scale is unrealistic. An 8" x 10" photo with a 300 ppi actually has more pixels than a 4" x 6" 300 ppi picture.

Another problem arises when you consider that printers are measured in dots per inch or dpi.  Printers use dots of ink to print, not pixels, and different printers use different numbers of dots for each pixel in a picture. The higher the dpi, the higher the quality of the print will be.

Pixels are made of various colors, contrasts, and brightness values; therefore, the more dots of varying colors and quantities, the better the image will be.

Quality photographic prints will require a printer that can print a resolution between 240 and 360 ppi, since this is the resolution required to produce a photo-quality image at a normal viewing distance. What this tells us is that we need to be aware of not only the ppi of the camera, but also the dpi of our printer in order to come up with photographic quality prints.