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Digital images are made of colored tiles known as pixels. Camera resolution, stated in megapixels (1 million pixels), indicates the maximum number of pixels the camera can use to create a photo. Chapter 2 discusses resolution in detail, but in terms of picture quality, you need to know just two key points:

 For onscreen photos, you need very few pixels. Resolution affects the display size of digital photos, but does not affect picture quality unless you greatly magnify your screen display. For most purposes, such as posting on Instagram or Facebook, a 1 MP (megapixel) image is adequate.

 For prints, you need lots of pixels. Figure 1-5 offers a look at the difference between a print with plenty of pixels (left) and one lacking in that department (right). With fewer pixels, it’s easier for the eye to detect that it’s looking at a bunch of squares. There simply aren’t enough pixels to finely render the details of the subject, and diagonal and curved lines appear jagged, or stair-stepped, along the edges.A general guideline is to aim for 300 pixels per linear inch (ppi) of the print size. An 8 x 10-inch print, for example, requires 2400 x 3000 pixels, or a resolution of approximately 7 MP. (Total image resolution is calculated by multiplying the number of horizontal pixels by the number of vertical pixels; 2400 x 3000 equals 7.2 million pixels.)

An important caveat: Not all pixels are created equal. The size of the image sensor that contains those picture building blocks must also be considered, as discussed next. The quality of the camera’s lens is critical, too — all the megapixels in the world can’t compensate for a poor lens.

FIGURE 1-5: A photo that has 300 pixels per inch (ppi) compared to one with a meager 50 ppi shows the impact of resolution on print quality.