When image transforming png to jpg, alpha layer become lined I have several png images that when transformed from png to jpg, the alpha layer is transformed to an horizontally lined pattern. 

Therefore I have to keep them as png, wich is in my case unnecessary and a drastic data load issue. 

The problem appears in production, wich is an ArcusTech server. 

Anyone knows what it could be ?

Thanks !
You'll need to have Imagick installed on your box if you want to preserve alpha channels in a PNG during transforms.

If Craft sees it is installed, it will use it by default.