Pixel Dimensions

Raster (bitmap) images, such as photographs, are made from a grid of tiny squares called pixels. Pixel dimensions are the number of pixels across the width and the number down the height of an image, written as width × height.

A photo of a school football team saved at 2400 × 1600 contains 3,840,000 pixels. Crop the same photo to 240 × 160 and it contains 38,400 pixels — one hundredth of the pixels.

More pixels allow an image to hold finer detail. Thin lines stay crisp, curved edges look smooth and small text remains readable. If you show two versions of a picture at the same size on a screen or on paper, the one with higher pixel dimensions packs more pixels into the same space, so each pixel is smaller and the picture looks sharper.

With too few pixels, the image has to be enlarged to fill the space. Each pixel becomes a visible block and the edges look jagged or blocky, which is called pixelated. For a given use — such as a large printed photo or a small on-screen picture — higher pixel dimensions generally give higher image quality, provided the extra pixels are actually needed at that size.

A huge pixel count mainly helps when the picture will be viewed large or zoomed in. A tiny thumbnail does not reveal the benefit of millions of extra pixels. Pixel dimensions also do not guarantee a good picture on their own: a blurry or badly lit photo stays blurry even at a high pixel count.