The white lines that appear on the artwork when exporting a PDF for graphic printing in the PDF/X-1a:2001 format are known as object division lines or “gaps” in visualization (stitching lines). These lines are not part of the actual artwork and will not appear in the final print. They occur due to how PDF viewers (such as Adobe Acrobat Reader) render objects for screen display.
Why do these lines appear?
1. Layer and Transparency Flattening:
• The PDF/X-1a:2001 format does not support transparency. When exporting, Illustrator “flattens” the transparency by dividing the affected areas into smaller parts, called tiles, to maintain the original visual appearance.
• During this process, PDF viewers may display white lines where the tiles meet. These lines are artificial and do not reflect actual issues with the artwork.
2. Screen Rendering:
• PDF viewing depends on how the reading software interprets vector and raster data. The white lines appear due to small rounding or rendering discrepancies.
Will these lines appear in the print?
No, they will not appear in the print because:
• In graphic printing, the tiles are properly merged by the printer’s RIP (Raster Image Processor) without leaving visible gaps or lines.
• The issue is purely visual and limited to on-screen display.
How to confirm the lines won’t appear?
1. Zoom In:
•If the white lines disappear or shift when changing the zoom level, this indicates they are just visual artifacts.
2. Print a Test:
•Print a sample to confirm there are no visible issues.
3.Toggle the “Smooth Line Art” Option:
• In Adobe Acrobat Reader, go to Edit > Preferences > Rendering and disable the “Smooth Line Art” option. This may help eliminate the display of the lines.
4.Use Acrobat’s Output Preview:
• In Adobe Acrobat, go to Tools > Print Production > Output Preview. This tool simulates how the file will print.
How to avoid future confusion?
• If possible, export the PDF in the PDF/X-4 format, which supports transparency and reduces the need for flattening, preventing this kind of issue.
• When working with transparency in PDF/X-1a:2001, make sure to review the flattening settings in Illustrator by adjusting them under Effect > Document Raster Effects Settings for higher quality.
This way, you can ensure the final artwork is accurate and free of visual artifacts in the print.
White Lines in the PDF When Uploading to Canva
If you’re editing the same PDF in Canva and the white lines also appear there, the answer is that these lines will not show up in the final print, as long as the file is properly prepared for printing.
Why do the lines appear in Canva?
Just like in PDF viewers, the white lines in Canva are caused by the transparency flattening process applied in the PDF/X-1a:2001 format. Canva renders the artwork for on-screen display, and these artificial lines may appear due to how it interprets the tiles created during flattening.
Ensuring the lines won’t show up in the print:
1. The lines are visual artifacts:
• In the graphic printing process, the printer’s RIP (Raster Image Processor) merges the tiles seamlessly without leaving any visible lines.
2. Use a reliable preview tool:
• Canva is not a dedicated tool for high-quality graphic file previews. To check the file’s integrity, use tools like Adobe Acrobat Pro and view the PDF using the Output Preview feature to simulate the print output.
3. Print a test proof:
•If you’re still unsure, print a test sample (either on a home printer or through your print provider) to confirm the result.
Important notes for editing the PDF in Canva:
• If you edit the PDF in Canva and make changes, the new export may reapply rendering or compression processes that could alter the file. To avoid issues:
• Use Canva’s highest-quality export settings, such as Print PDF (High Quality).
• Ensure Canva preserves the color mode in CMYK, which is required for professional printing. Check this option in Canva before exporting.
Conclusion:
Even when editing in Canva, the white lines will not appear in the final print. They are merely visual artifacts caused by on-screen rendering. However, to ensure the overall quality of the file, it’s important to use proper export settings and, if possible, consult your print provider about the ideal format.