Checking image quality

You may often want to check the quality of a particular image to determine if it is sufficient for printing. So below we have put together a few pointers on how to do this from your PC or Mac.

The number of pixels in your image

Every image you see on your screen is made up of thousands of pixels. A pixel is a colored dot on your screen. The more dots the image contains per inch of screen, the better it will display.

PC: To check how many pixels your image contains open it in Windows Explorer, locate the image and select it to view more detailed information. Alternatively you can right click on the image to view its Properties and then select the Details tab. Here you can see the width and height in pixels. This screenshot shows the dimensions for an image called mountain river.jpg. We can see that this image is 3456 pixels wide and 2304 pixels high.

Mac: Open Finder to select the image, then right click to Get info. The number of pixels should then be shown as the dimensions of the image. See the example in the screenshot below.

The quality of your image

Now you know the number of pixels in your image, you can estimate its quality. As a rule of thumb, to ensure your images print properly they should have a minimum of 300 ppi (pixels per inch) at the physical size they will be printed.

So, for example:

The mountainriver.jpg image is 3456 pixels wide and 2304 pixels high, what’s the largest we can print it?
3456 / 300 = 11.52″
2304 / 300 = 7.68″

This image is to appear on the cover of a landscape 9″ x 6″ book and we can see the image quality is perfectly good enough for that.