Understanding resolution

Understanding resolution is essential to making prints that look good. This article discusses, in the simplest way possible, what resolution is, and when it’s important.

Pixels

The images your camera produces are made up of tiny square shaped pixels. If you open an image in Photoshop and zoom in far enough, you’ll eventually start to see the colored square pixels that make up the image. Pixels alone don’t have a specific size. They can be really small or quite large. The resolution of an image is what determines how big or small the pixels are.

image pixels

Resolution

Resolution is essentially a measurement of pixel density. It’s the number of pixels on one side of the image divided by the size of the output (print). The higher the resolution, the smaller and more densely packed the pixels in the image will be. An image with 3000×2000 pixels would have a resolution of 500 ppi when printed at 4×6 inches (3000/6=500). If you were to make a larger print like an 8×10, the print would have a lower resolution of 300 ppi.

The only time that resolution really matters is when you print your images. Digital displays like your computer monitor have a set number and size of pixels no matter how dense the image is. The standard ppi for web images is 72 ppi, although if you alter from that slightly it doesn’t really matter. If you upload an image that is 800 ppi it will look exactly the same as the 72 ppi image, except it will take longer to load and take up a lot more space on the server.

Using the same image of the monarch again, look at the images below.

72 ppi

This image was saved at the standard web resolution of 72 ppi. The image has smooth transitions and looks good.

240 ppi

Can you tell the difference between the first image and this one?

This image was saved using a much higher resolution of 240 ppi, but it looks exactly the same on screen. Since your monitor has a set pixel size and resolution, the images are displayed identically.

If you were to print both images, the second would make a much higher quality print. Printers can produce much smaller dots than a display, and can take advantage of higher resolution images.

Resolution for print

When you print images, the resolution becomes very important. Printers measure resolution in dots per inch (dpi). The term dots is used because printers use thousands of tiny dots to produce the illusion of a smooth image surface.

An image with a high resolution will produce a high-quality print with very small dots and smooth transitions. An image with a much lower resolution printed at the same size would have much larger pixels and produce a print of much lower quality. The higher the resolution of your image, the larger size of print you can make with it and still get a high quality result.

Printed images require a much higher pixel density than images used on the web. For smooth high-quality prints, use a resolution of 240 dpi. The chart below shows the minimum image resolution needed to create different print sizes at 240 and 300 dpi.

resolution for print size