“Hello, how can I help you?”
“Well, I’ve brought a digital picture I downloaded from the internet; can you enlarge it to, say, A2 size?”
What is resolution and why is it important?
Let us start with a definition. Image resolution is really the density of an image, which is obtained by counting the number of pixels that a digital image contains within a certain area. This determines the quality and size of the image.
Resolution in print is measured in dots per square inch, also known as DPI. This refers to the number and spacing of CMYK dots in a printed image. Resolution of a screen is measured in PPI – pixels per square inch of a screen.
A simple rule: the more dots or pixels within this small area, the better quality of the image file. Logically, it follows, the denser the dots or pixels, the bigger the size of the file.
However, please do not confuse DPI and PPI. If you set to design your piece at 300PPI it will not reproduce at 300DPI! Remember, PPI is a measure for your screen; it is not dots but pixels. Chances are that your design will look great on the screen set to 300PPI but you will be disappointed with its printed version.
Typically, screens use 72PPI resolution, although there are some systems which handle up to 96PPI – to make most of animation and show images in crisp detail. Be warned, this is not enough for printed output.
The adopted standard in resolution for commercial printing is 300DPI at the size you would like your image to be printed. Anything less than this will look blurry or pixelated, anything more will just unnecessarily make your print ready file too large to handle.
For large format, posters and billboards, you may use resolution of 150DPI, as when images are seen from further distance, the detail is not as crucial. The bonus is also a manageable file size.
If you have trouble sourcing a good quality image and the only one you really want is taken from the internet and therefore low resolution, you can get away with using it, but it means compromising; to fool the eye you will have to print it very small.