Products module - ignoring alpha channel on product image resize

[luminous]

A friend of mine uploaded a lot of pictures into the products module yesterday, only to find that the reszied preview and thumbnail images developed a black background.  The original images were .png format and had a transparent background.  The produced previews and thumbnails were called .png, but were actually jpegs - obviously the transparency was lost.

Example, the "Bamboo Body Beater" at the top of the page should have a transparent background - no black at all:
http://www.teessidekungfu.co.uk/online-shop/iron-palm

(site is still in development, so there will be "strange things" happening from to time).

I am aware that an obvious immediate solution is to ftp into the server, and find the preview and thumbnail images.  I can then edit the original image and replace the offending images on the server.  

[Dr.CSS]

Most likely Products module is using the default image manager to make thumbs and it can't handle transparent png, sorry...

[ajprogramming]

Customizing the resize method will be needed, and watermarks probably won't be able to be used.

Because the Products/CGExtensions is setup to work with adding watermarks having images with an alpha channel is extremely difficult.

[luminous]

Ahh, fair enough.  Cheers for the replies

I guess I am showing my ignorance again, as I thought the watermarking would be using the alpha channel and would therefore be able to cope with what I was wanting.

No matter, I will just connect and manually sort it out