What size photo do I need for printing? Why are some photos blurry when enlarged? What is resolution? These are all common questions that come down to one tiny unit: the pixel.
What is a pixel?
You can see the pixels that make up your photo when you zoom into an image – they look like squares in a mosaic (see fig. 1). Pixels are literally the building blocks of the common image types: JPG, PNG and GIF.
There are a finite number of pixels in an image. When you enlarge an image, that mosaic of pixels becomes larger – and more visible. This is when your image starts to look blurry.
Print resolution and pixels
The number of pixels that make up your image affects the print resolution of your image. Print resolution is measured by pixels per inch, or PPI. PPI is exactly what it sounds like: a measurement of how many pixels are in a square inch of your image.
To achieve a crisp, quality image during printing, PPI needs to be a minimum of 300. Anything below this minimum can produce an unwanted blocky or blurry look.
When you need a graphic or illustration that can scale to any size, the best solution is to use a vector graphic. Vector graphics use paths (or lines) instead of pixels to build an image. Therefore, vector files are scalable and can be resized to any dimension (see fig. 2).
Vector graphics need to be created in a program specifically designed for these file types. The standard vector file formats are .ai and .eps.
What you need for the best results
If you have a pixel image, remember to use a resolution of 300ppi or better. These files are usually JPGS or GIFS. Vector files, however, can be printed at any size, and are often AI or EPS files.
Your graphic designer can help you choose images and file types to help you create a pixel-perfect design. Questions? Drop us a note at firstname.lastname@example.org