Thumbnails get black background

When upload a image (transparent .png) the background got a black background.

We want the same transparent background, where can I change this?

Hi Raimond

I am sorry. This is a known issue but we haven't had a solution yet. We use Joomla API to resize the image but it still has this issue with transparent image. Could you please use image in different format (no transparent images) ?

Regards,

Tuan