Controlling the print size and quality of digital images requires an understanding of the pixels-per-inch (ppi) variable that is stored in the image file and sometimes used to control the size of the printed image.
These parameters work together to produce a printed image of the desired size and quality.The Image Size dialog can be used as an image calculator of sorts. For example, a 1600 x 1200 image with a ppi of 200 will produce a printed image of 8 x 6 inches.
Within the Image Size dialog (as it is called in Photoshop), the image editor allows the user to manipulate both pixel dimensions and the size of the image on the printed document. Pixels per inch of the image, pixel per inch of the computer monitor, and dots per inch on the printed document are related, but in use are very different. The same image with a ppi of 400 will produce a printed image of 4 x 3 inches. Change the ppi to 800, and the same image now prints out at 2 x 1.5 inches. All three printed images contain the same data (1600 x 1200 pixels) but the pixels are closer together on the smaller prints, so the smaller images will potentially look sharp when the larger ones do not. The quality of the image will also depend on the capability of the printer.
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