Photo Enlargement – Understanding Dots Per Inch (dpi)

A fun and creative way to display your favorite photos is to print photo enlargements. When creating photo enlargements an important point to keep in mind is to maximize the dots per inch or DPI of your image file, but what is DPI, how does one determine DPI and what is a good DPI number? This article answers those questions and provides tips on how to create high-quality photo enlargements.

Dots per inch is defined as the number of dots contained within a linear inch on a printed material. DPI is determined two factors: the number of dots that a printing machine is capable of placing in a linear inch and the number of dots provided by an image for each square inch of printing real estate. For example, a consumer printer will display the maximum number of dots per inch it is capable of printing on the specifications label. This does not mean that the printer will always print at the stated maximum DPI, but if the user sets the printer at the highest settings and use the prescribed printing materials it will print at maximum DPI. Now, in order for the printer to print at the maximum DPI, the image supplied must also contain an adequate number of pixels or dots.

To check the DPI of a digital image on a Windows operation system computer, right click on the image file and select the properties menu option. Click on the summary tab and click the advanced option. This should display the vertical and horizontal DPI in a table format.

A good DPI number varies for every application. This article will focus on DPI numbers for photo enlargements. To calculate the DPI for your photo enlargement, you must first choose the size of the photo you wish to print. For demonstration purposes, we will say the photo we wish to print is going to be 12x12” inches. A standard 8 megapixel camera will deliver an image roughly 3200x2400 pixels large. A pixel in digital formats is considered a dot. The printed material is square in shape so the image must be cut to fit the image. We can cut from the horizontal width 800 pixels and create a 2400x2400 pixel image. If I were to use that image for a 12x12” inch photo print, I could calculate the DPI by simply dividing the number of pixels by the number of inches on each corresponding side. In this example, we would divide 2400 pixels by 12 inches and discover that we could print a 200 DPI image. An image printed at 200 DPI is considered excellent. A professional quality image ranges over 300 DPI, but consumer photo enlargements can vary as low as 100 DPI. If you wish to create an extremely large image such as a 60x100” print, a standard digital camera would not be able to deliver 100 DPI. However, if your photo enlargement is viewed from a distance, your eye will blend the pixels and create great looking photos.

Always calculate the DPI of your to photo enlargement printing orders to ensure that you create a wonderful looking photo