Steps to reproduce the issue

The plugin https://github.com/ttc-freebies/plugin-responsive-images is using this library "joomla-cms/libraries/src/Image" in order to create many smaller images for mobiles of jpg and webp format.

Expected result

Normally the transparent areas in the PNG images should stay transparent.

Actual result

When using PNG images with transparency, the transparent areas change to black.

System information (as much as possible)

Joomla v. 3.9.19

Additional comments

Is there a way to fix this issue because png image with transparency are very common.