Some PDF thumbnails are showing a black background

Applies to a few MysticThumbs builds with versions before 4.6.2

This is a side effect of having PDF files appearance transparency setting on Opaque.

In these older versions, black is used to clear the thumbnail background, and if the PDF has transparency then that is what you see as the canvas. This has been improved with newer versions since 4.6.2 that now allow setting each file extension’s transparency background canvas.

To fix these older versions:

  1. Open the control panel and select PDF extension
  2. Change appearance transparency setting to Canvas or Transparent.
  3. Apply the changes
  4. Either:
    1. Clear the thumbnail cache
    2. Manually refresh affected thumbnails using the File Explorer context menu (right click on the file)