PDF image covers are inverted in thumbnails

Hi all,

One of my colleagues batch uploaded a number of PDFs of our university magazine, but the thumbnails show the negative of the cover. However when we go to the direct file, the PDF displays normally in each record. Is this a case with having to manipulate something within the PDF files themselves or is my thumbnail plugin acting up? I’ve never come across this issue so far, so I’m wondering if anyone else has and if they have any easy fixes.

Thank you all for your help!


I met the same issue here today. After some research, I think it’s due to how ImageMagick handles the pdf file with the color model in CMYK. As long as the pdf file’s color mode is RGB, the generated thumbnail will be fine. So the solution can be either convert the original pdf’s color mode to RGB or switch the setting of “fileDerivatives.strategy” in “application/config/config.ini” to a different value. BTW, The “Omeka_File_Derivative_strategy_GD” can not generate thumbnails for pdf files properly.

My recollection is that the last time this came up, I wasn’t able to reproduce the problem. So it’s at least partially just an issue of versions of ImageMagick and/or Ghostscript fixing this problem.

I’m happy to try again if you have an example problematic PDF.