The number of pixels n for a given maximum resolution (w horizontal pixels by h vertical pixels) is the product n = w × h. This yields e. g. 1.92 megapixels (1,920,000 pixels) for an image of 1600 × 1200. The majority of compact as well as some DSLR digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3. [1]. According to Digital Photography Review, the 4:3 ratio is because “computer monitors are 4:3 ratio, old CCD’s always had a 4:3 ratio, and thus digital cameras inherited this aspect ratio.”[1]

The pixel count quoted by manufacturers can be misleading as it may not be the number of full-colour pixels. For cameras using single-chip image sensors the number claimed is the total number of single-colour-sensitive photosensors, whether they have different locations in the plane, as with the Bayer sensor, or in stacks of three co-located photosensors as in the Foveon X3 sensor. However, the images will have different numbers of RGB pixels: the Bayer-sensor cameras produce as many RGB pixels as photosensors via demosaicing (interpolation), while the cameras with Foveon sensors produce uninterpolated image files with one-third as many RGB pixels as photosensors. It is difficult to compare the resolutions based on the megapixel ratings of these two types of sensors, and therefore sometimes subject of dispute.