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Either I'm missing something (or have something badly configured in my self-hosted blog network) or when I'm uploading a transparent .png file (with alpha channel) using Media Library, my Wordpress installation makes all possible cropped versions loosing transparency.

This way, when I'm picking a perfectly transparent image for my site icon, I end up with favicons having ugly looking white background. To make things even worse, Wordpress' Media Library uses some weird size reduction algorithm, which causes my perfectly white / transparent background to be composite with all different shades of white / gray on all cropped images.

Is there any way to workaround this problem? Is this something in my configuration or is this another bug (loosing transparency / alpha channel when resizing image couldn't be a feature).

The only way I found to workaround this, is to download all cropped image files (after upload) through FTP, manually correct them (add transparency or fix background color) and re-upload them back, overwriting files generated by Wordpress. But, that sounds like a madness...

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  • Does this only happens for site icons or do you see the same thing happening when you upload a transparent png file through the media library? It worked for me few days ago with such a file.
    – birgire
    Sep 8, 2015 at 13:37
  • @birgire No. As I stated in the first line of my question: "(...) when I'm uploading a transparent .png file (with alpha channel) using Media Library (...)" -- that means, that this happens always, no matter what destination for uploaded image is.
    – trejder
    Sep 8, 2015 at 18:44

1 Answer 1

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There used to be an issue with WordPress – but that should have been fixed 5 years ago: Preserve PNG transparency/alpha during thumbnail creation

If you're using a newer WP installation (which I suppose) this issue might be rather a problem with the GD library of your server than with WordPress. And as far as I know this issues only occurs with 8bit pngs. Using 24bit pngs you should be on the safe side.

I found this 'suggestion' over at the wordpress support forum. However I can not confirm this 'bug-fix' myself since my webserver seems to render both 8 bit and 24 bit images just fine (tested here with WP 4.3, GD bundled 2.1.0 compatible, PHP Version 5.3).

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  • You have most certainly hit the point with that 8-bit .png file, which I was making somewhat automatically from 24-bit source files. Without conversion to 8-bit and with uploading 24-bit file through Media Library, everything seems fine about alpha channel and transparency. Thank you...
    – trejder
    Sep 8, 2015 at 19:17

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