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What is Resolution? DPI, PPI and Megapixels

Resolution Explained

Resolution is a somewhat broad concept. At its core, it refers to a measurement of an image’s quality. The complexity shows up when you break resolution down into its specifics, namely DPI, PPI and MP. The key thing to understand is that each particular measurement plays a fundamental role toward an image’s appearance.

Megapixels (MP) Tutorial

A single MP refers to 1 million points, dots or pixels on a digital image. This measurement is used most commonly when talking about digital cameras. One that shoots at 8 MP, for instance, captures photos using 8 million pixels. The Canon Rebel XT captures photos at a 3456 x 2304 resolution, which when multiplied comes out to 7,962,264 pixels. This makes it an 8MP digital camera.

Pixels-Per-Inch (PPI) Tutorial

PPI affects the print size and quality of your image. If the PPI is too low and there aren’t enough pixels per pinch, each pixel will come out very large. This results in pixilated, blurry images chockablock with jagged edges. Pretend you are dealing with a 100 by 100 pixel image. If you set it to 10 PPI, then you will wind up with a 10-inch by 10-inch photo. If you set it to 100 PPI, on the other hand, you will end up with a 1-inch by 1-inch image.

Dots-Per-Inch (DPI) Tutorial

DPI is like PPI, but it points to the number of dots of ink that will be printed per each inch of the image. When printed, every image pixel contains dozens of tiny dots. Each dot corresponds to one of the major colors. A higher DPI rating therefore permits a printer to combine more colors together and thus create more realistic tonality. This results in a higher-quality image that looks better, smoother and more real.

Combining DPI And PPI

Where things get complicated is when you combine PPI with DPI. Suppose you are dealing with a 1200 DPI printer. This means that every square inch of the printed image will contain 1200 * 1200 dots. This comes out to 1.44 million dots. Now suppose you want to print a 300 PPI image. Every square inch of this image contains 300 * 300 pixels. This comes out to 90,000 pixels. This means that every printed pixel will contain 16 dots (1.44 million dots divided by 90,000 pixels).

From Image Capture To Image Export

The three components of resolution, namely MP, PPI and DPI, each play a role in the process of digital photography. You use MP to capture the image. You use PPI to prepare the image for printing. And then you use DPI to print it. The general rule of thumb is that you want high MP, PPI and DPI rates. However, each case is different, which is why it’s important to understand and correctly apply this knowledge. How you use this knowledge is up to you.