Decode Moire
“Halftone Moiré” is jargon from the printing industry, referring to an unwanted visual effect in printed images. To understand it, we need to decode its two parts:
- “Halftone” is a method that tricks our eyes into seeing shades of grey in a black and white image. This is achieved by varying the size and density of tiny dots that make up the image.
- A “Moiré pattern” is a unique visual disturbance that occurs when two similar patterns interfere with each other. This interference creates an undesired, wavy look.
So, “Halftone Moiré” happens when the dot grid of a halftone image clashes with another similar pattern, causing this unwanted wavy appearance.
For high-quality print results, it’s essential to prevent Halftone Moiré. When the halftone patterns aren’t correctly matched, they can create this odd effect, ruining the final image. To avoid this, careful management of color separation and halftoning is necessary.
Here are some tips to prevent Halftone Moiré
- Maintain Full Vacuum and Correct Exposure: Keep full vacuum during exposure and avoid overexposure.
- Stay Consistent: Maintain uniformity in all production variables for halftone images, like using identical halftone angles and line count for similar tasks. Consistency makes it easier to spot problem areas leading to Moiré.
- Verify, Don’t Assume: Check all specifications before starting. Ensure all materials and tools match their given specifications.
- Set Halftone Angles: The angles for contrasting colors should be 30 degrees apart. This creates a less disruptive pattern called a rosette, which is more aesthetically pleasing.
- Be Methodical: Note all details of your printing process. Documenting everything helps in tracking when and why Moiré occurs.
- Rotate the Halftone Set: Slightly changing the standard halftone angles can help reduce Moiré. The best rotation degree varies depending on your equipment and software.
- Choose Appropriate Halftone Line and Mesh: A high mesh-to-dot ratio can lessen the chance of Moiré. This involves selecting the highest possible mesh count and the lowest possible halftone line count.
- Select the Right Mesh: Go for a mesh with maximum open area and thinnest thread to reduce interference between the halftone dot opening and the mesh thread.
- Manage Emulsion-over-mesh (EOM): EOM should be between 8 to 12 microns. An incorrect EOM can cause improperly formed dots or prevent the fine dots from transferring to the substrate.
- Use Pin Registration: This helps to accurately position the image relative to the screen, ensuring the halftone angle matches the mesh threads’ orientation, crucial for preventing Moiré.
Keeping these tips in mind can help reduce Moiré in your printing process. It’s always best to handle this systematically and consistently to manage all involved variables effectively.
