Print glossary

What is a raster image?

Definition

A raster image is made of pixels, like a JPEG, PNG or photo, and goes soft or blocky when enlarged beyond its resolution.

What it means for your file

Photos are always raster. Logos saved as raster images are the most common cause of blurry print.

Raster file types include JPEG, PNG, TIFF, GIF, PSD and HEIC. A PDF, EPS or SVG can hold vectors, raster images or both, so the file type alone doesn’t tell you which you have: zoom in to 800% and see whether the edges stay crisp.

An example

A logo saved as a PNG 500 pixels wide prints sharp at about 1.7 in wide, at 300 ppi. Stretched to 6 in wide for a sign, the same image is only about 83 ppi, and its edges turn soft and stepped. The same logo as a vector prints sharp at any size.

A common mistake

Opening a JPEG in Illustrator and saving it as AI, EPS or PDF to make it a vector. The file type changes, but the picture inside is still the same pixels. A raster logo has to be redrawn, or auto-traced and then corrected by hand, to become a real vector.

How to fix it

If your printer sent the file back saying “The images are low resolution,” the fix page has the step-by-step way to do it yourself, and a fixed price if you’d rather have it done.

How to fix “The images are low resolution”

Free tool for thisCheck an image’s DPI at print size, free Is this image big enough? How large can it print? Pixels needed for any size.Check if a pattern is seamless, free See your tile repeated, find the seam where the edges don’t meet, and the size one repeat prints at 150 and 300 ppi.