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SharePoint thumbnails of PNG files with transparency

The problem

You uploaded a PNG file with a transparent layer to SharePoint. Everything went fine, except the thumbnail and preview of your image: everything that is supposed to be transparent is now black.

For example:

The reason

For every image file, SharePoint creates a thumbnail and a preview and saves them as JPG files. But JPG doesn’t recognize transparent pixels and so it replaces them with black pixels.

SharePoint saves thumbnails and previews in a hidden folder of your library, such as:

  • sharepoint.company.com/software/illustrations/_t/ for the thumbnails (the hidden folder is ‘_t’)
  • sharepoint.company.com/software/illustrations/_w/ for the previews (the hidden folder is ‘_w’)

To find the exact URL:

  1. Right-click the thumbnail or preview and click Properties.
  2. In the dialog box, the URL is visible under Address (URL).

SharePoint replaces the dot of the initial file extension with an underscore, and adds '.jpg’ at the end of the file name: ‘Approved.png’ becomes ‘Approved_png.jpg’.

The solution

  1. Open the PNG file in a photo editor.
  2. Save it as a JPG file, but make sure the file name ends with _png.
    You saved it as a JPG, so all transparent pixels are now white pixels.
  3. Go to the hidden thumbnail folder.
  4. Open this folder in Windows Explorer
  5. Copy the file (example_png.jpg) to this folder and confirm you want to replace the existing file.
  6. Repeat steps 3 to 5 for the hidden preview folder.
  7. Go back to your library and check if the thumbnail and preview are now replaced by the new one.

If you cannot open a SharePoint folder in Windows Explorer, you can also upload the file using SharePoint. In that case, you will not see the file you have uploaded in the Sharepoint list because the folder is hidden.

sharepoint/sharepoint_thumbnails.txt · Last modified: 2017/03/30 13:16 (external edit)