20 min read

Pixels and Resolution

Digital images are grids of pixels. Resolution — pixels per inch — decides how sharp an image looks at a given size.

Pixels

Zoom into any photo far enough and you see the squares. The number of pixels across and down is the image's pixel dimensions, for example 3000 \times 2000 px . More pixels means more detail can be recorded.

More pixels, more detail

This picture has 32 × 32 = 1,024 pixels.

Print size calculator

Width (pixels)Height (pixels)

Resolution

Prints at 21.0 × 29.7 cm (8.27 × 11.69 in). Uncompressed at 24-bit colour: about 26.1 MB.

Try it:

Choose 8 \times 8, then 256 \times 256. The picture is the same size on screen, but with more pixels the edges become smooth. Then try the print calculator below it.

ppi vs dpi

$ppi (pixels per inch)$	$dpi (dots per inch)$
$About the image : how many pixels fit in each inch$	$About the printer : how many ink dots it places in each inch$
$You set it in Photoshop (Image Size)$	$A setting of the printer$
$300 ppi for print, 72 ppi is a traditional screen value$	$Printers use many tiny dots to make each pixel's colour$

People often say "dpi" when they mean ppi. For your work: set 300 ppi for anything printed . On screens, only the pixel dimensions matter — a 1920-pixel-wide image fills a Full HD screen whatever its ppi setting says.

Practice

A camera takes photos 6000 \times 4000 pixels. How many megapixels is that? (1 megapixel = 1,000,000 pixels)

Your answer