same problem. need png for some goods, but when uploading png images, K2 converts them into jpg. it's a big problem - first time i tried this component and such fail. three days gone, no job done. hope, some solution will come after more than year this question appeared first time. but I find it hard to believe. но надежда умирает последней....

Hi...new here,

If you look in administrator/components/com_k2/models/item.php around line 200 you'll see the images being converted according to size. Change jpg to your desired extension and then in components/com_k2/models/item.php around line 110 change the corresponding size extension.  Not a great solution (a pretty bad one actually) but it saved me in a crunch.

 

Hope this helped.