On screen, a scaled-up image can look acceptable because the display is low resolution. In print, the same image at the same size will show softness or pixelation. Effective PPI at output size is what matters.
Effective resolution
When you place an image and scale it up, the number of pixels per inch drops. A 300 PPI image at 1" becomes 150 PPI at 2". Below the printer's minimum, the print will look soft or pixelated.
How to avoid it
Supply images at final size and at least 300 PPI (or the printer's minimum for large-format). Do not rely on scaling in layout to "fix" a small image. Check effective resolution in your design app before export.
Before you send the file
• Confirm image dimensions at 100% in layout match final trim size.
• Ensure effective PPI is at or above the printer's minimum.
• Replace any image that shows as low-res in the Links or preflight panel.
Common mistake
Approving a proof on screen and not checking effective resolution. The proof may look fine at zoom level; the press will show the true resolution. We check and flag low-res images.