Each colored box represents a certain number of megapixels. The numbers along the top and left side are print dimensions in inches at 300ppi (pixels per inch). Most books and magazines require 300ppi for photo quality. For example, the chart shows that you can make a 5" x 7" photo quality print from a 3 megapixel camera.
inches @ 300ppi (numbers inside colored boxes are megapixels)
Notice that as the print size doubles, the megapixels required increases geometrically. You can make nice 8" x 10" prints with a 6 or 8 megapixel camera, but to make a true photo quality 16" x 20" print, you need between 24 and 30 megapixels. Don't be fooled by manufacturers' claims that say you can make 16" x 20" prints from an 8 megapixel camera. While you certainly can make a print that size, it will not be true photo quality.
Information and chart provided by design215.com. For more information go to http://design215.com/toolbox/megapixels.php.
