Looks perfectly sharp on screen, comes back soft or pixelated from the printer.
Almost every time, the answer is the same: the file is fine for a screen and not fine for a press, and nothing on screen tells you that.
A monitor shows roughly 72 to 110 pixels per inch. A commercial press wants about 300 pixels per inch at final printed size. So an image can fill your screen crisply and still carry only a third of the detail the press needs. You cannot see the problem by looking, because the thing you are looking at is the low-resolution version.
The number stored in the file is not the number that prints. What matters is effective resolution: the image’s actual pixel count divided by the size it is placed at on the page.
A 1000 x 1000 pixel logo placed in a 1 inch box is 1000 PPI, far more than needed. The same logo stretched across a 10 inch box is 100 PPI, and it will print soft. Scaling an image up in your layout does not add detail; it spreads the existing pixels thinner.
This is why “but the original was high resolution” is so often true and so often irrelevant.
Open the effective resolution of every placed image, not the document resolution. Look for anything under about 300 PPI at final size. For large-format work such as banners and signage the acceptable figure is lower, because viewing distance is greater, but the principle is identical: resolution is only meaningful relative to printed size and viewing distance.
This is one of the few problems Filecheck will flag but not silently correct. Upscaling invents detail that was never captured. Some tools will do it and produce something that passes a resolution check while looking soft or artificial in print, which is worse than an honest warning, because it fails quietly.
The fix is a higher-resolution source image, or placing the existing one smaller.
The reason this is expensive is timing. You find out after the customer has approved, after the job has been scheduled, and sometimes after it has printed. Checking effective resolution at the moment of upload moves the conversation to the point where the customer still has the original file open and can simply supply a better one.
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