The pixels in an image become individually visible when the image is expanded enough, due to the finite number of pixels in the image and relatively unlimited viewing size of the image. The threshold at which the image becomes pixelated varies based on the resolution of the image, with low-resolution images becoming pixelated at lower zoom levels due to having fewer pixels.
Pixel resolution measurements state the number of horizontal pixels by the number of vertical pixels. For example, an image with a pixel resolution of 300 x 300 has 300 rows and 300 columns of pixels for a total of 90,000 pixels.
Resolution can also refer to the number of pixels per unit of length or width. Graphic designers typically measure this resolution in inches and refer to the number of pixels that fit in an inch as "dots per inch." Images with low dpi, such as 60 to 90 dpi, are considered low-resolution and are more likely to appear pixelated at lower zoom levels.
The number of pixels in a photographed image is limited by the capabilities of a camera. The camera's megapixel rating reflects the approximate number of pixels the camera can capture in a single image, calculated in millions. An eight-megapixel camera, for example, can take images up to a pixel resolution of 3,546 x 2,304 for a total of 7,962,624 pixels.