Editing Pixel density (section)

== Outputting to a different device ==
When moving images between devices, such as printing an image that was created on a monitor, it is important to understand the pixel density of both devices. Consider a 23″ HD monitor (20″ wide), that has a known, native resolution of 1920 pixels (horizontal). Let us assume an artist created a new image at this monitor resolution of 1920 pixels, possibly intended for the web without regard to printing. Rewriting the formula above can tell us the pixel density (PPI) of the image on the monitor display:
:<math>\text{PPI (monitor)} = \frac{\text{Number of Pixels}}{\text{Size in Inches}} = \frac{1920}{20} = 96\text{ ppi}</math>

Now, let us imagine the artist wishes to print a larger banner at 48″ horizontally. We know the number of pixels in the image, and the size of the output, from which we can use the same formula again to give the PPI of the printed poster:
:<math>\text{PPI (poster)} = \frac{\text{Number of Pixels}}{\text{Size in Inches}} = \frac{1920}{48} = 40\text{ ppi}</math>

This shows that the output banner will have only 40 pixels per inch. Since a printer device is capable of printing at 300&nbsp;ppi, the resolution of the original image is well below what would be needed to create a decent quality banner, even if it looked good on a monitor for a website. We would say more directly that a 1920 ×&nbsp;1080 pixel image does not have enough pixels to be printed in a large format.