In Providence 1.7.8, when we import PNGs with a transparent background the preview is rendered as a jpg with black background.
Is there a setting to make it white instead?
Implemented. See https://github.com/collectiveaccess/providence/pull/762 for notes.
Support for Gmagick, GraphicsMagick and GD is implemented. ImageMagick support should be there but has not been fully tested. Imagick support is largely a guess as I have no environments running Imagick currently, and don't have time to set that up. If you are running Imagick or ImageMagick please let me know if it works ok.
Also note that zooming tilepic support may be iffy. The hoops we have to jump through to make this work require re-compositing the image. For a few previews this isn't that big a deal to do, but for thousands of tiles it adds a lot of overhead. I'm guessing if you're uploading images with transparency they're relatively low-res and zooming isn't that important. If that's a poor assumption let me know and we'll look into the issue further.
We’ll have to add one.