There always seems to be confusion from clients on what size of image/photograph is good enough for print. We are often emailed a selection of images which are all around the 59KB mark; these are usually images which have been lifted from websites. We have to explain that such images won’t print well because the image resolution is too low.
Here is a little more information to help explain further. The resolution of an image refers to the density of the pixels (or printed dots) of which it is made up of. When images are at a high resolution, they appear crisp and sharp. If the resolution is decreased or the image is enlarged too much, it loses detail and the blocky squares of the pixels become clear. If you remember how TVs from the ’80s looked, they would appear fuzzy and washed out today compared to HD – high resolution makes all the difference!
Web Resolution vs. Print Resolution
Screen resolution is measured in PPI (pixels per inch) and print resolution is measured in DPI (dots per inch), though the terms are often used interchangeably. Because the entire viewing area on a computer screen is made up of pixels of a fixed resolution – typically 72 to 100 dpi – any image optimised for this resolution will look detailed and natural to the human eye. Therefore, using an image size of 59KB at 72 dpi will be perfectly acceptable for web and screen use.
But if that same image is printed at full size, its inherent pixel ‘blockiness’ becomes too obvious and unacceptable for print.
For professional printed/exhibition images, 300 dpi is the standard. If you want to use a web image in print, you will run into problems.
For example, for a full page A4 image, you would be looking at a photo/image size of 17MB.
When you have a choice of image sizes at your disposal, such as from an in-house image library or stock photo site, it’s best to go for the largest image available. Any image can be made smaller as needed, but an image cannot be increased in size without losing quality.