The Moiré effect or, in other words, a halftone overlay, is a common phenomenon when viewing prints. It occurs when two even patterns overlap unevenly.
When does Moiré appear?
Moiré always occurs when screens overlap. Typical examples:
- You have scanned in a newspaper ad and print it in another newspaper.
- You print the portrait of a managing director wearing a jacket with a fine houndstooth pattern, a checkered shirt and a finely patterned tie. Regardless of the printing process, complete Moiré chaos is guaranteed to break out here.
- A brick building is reproduced in offset printing.
- The photograph of a ventilation grille is viewed on a monitor
You can find further information here:
What is Moiré? And can I see Moiré in a proof?