Is transparency supported by this tool?

[Destroy666x]

I am using the web version and e.g. a PNG with 4 transparent corners, like this one:

gets the corners either completely removed with lower number of color precision or only 1 corner (top left) has some grayish non-transparent color.

Am I missing something? Can transparency be preserved somehow? Otherwise great tool.

[Destroy666x]

Ok, I see that for some reason the desktop version is very different and has way better transparency support. Why?