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Why do some publications created from PDF files display fractional white lines?

Sometimes, when the publication is created from a PDF file, it may display fractional white lines while the original PDF seems to have no problem. Sometimes the white lines can be seen to a lesser extent in the original PDF file, and sometimes they may appear or disappear when zooming in or out.

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Note: When you upload your PDF file to Joomag it is being converted to SVG format and displayed on an HTML5 viewer. This process gives you the possibility of enhancing your publication with additional interactive elements.

This happens when the PDF file uses clipping with very tight tolerances and is typically seen in files that split images into smaller tiles. It is more commonly seen in files produced by InDesign, though the reason why the images split that way is unknown.

These files rely on a feature of PDF called Scan Conversion. Scan Conversion is a process controlled by the renderer which determines how to paint a pixel when content only partially overlaps it.

The PDF specification calls for very forgiving scan conversion to fully paint a pixel even when content only partially overlaps it. However, converting to HTML and SVG means that we rely on the web browsers to render the content which unfortunately means we do not have any control over this process.

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