The devil is in the details. There are ways for user’s to specify that they want an image exported as JPEG (see image)
There are also many ways for a 3rd party stack to modify an image. The Stacks-API gives all the same controls that user’s have when editing a image – to the stack developer too. So they can specify (for example) that all images should be exported as JPEGs if they think that’s best – or PNGs if that’s what they need.
So, in general, the decision to export PNG could be:
- a setting that you chose.
- some detail about the image.
- just what that stack does.
- a setting in the stack.
- or some combination of all of the above.
Of course, I can provide really specific detail of why an image exports exactly like it does – but I’ll need really specific detail about the project file.
You can also probably learn a lot by experimenting a bit:
- what happens if you drop the image onto a page by itself. still JPEG? or does it stay PNG?
if it’s coming out JPEG here – without you doing anything at all. then it’s probably something about the image – something is telling Stacks that this image wants to be exported as a JPEG.
- what happens if you drop the stack in a page by itself and then put the image into it? still JPEG? or PNG?
if it’s coming out JPEG here – with the default settings of this stack – then it’s probably the default behavior of that stack. you’ll probably want to take a deep look through to see if there are settings that allow you to change that. if there aren’t, then it’s time to talk to the developer of that stack.
if it’s coming out as PNG in both cases – then it’s something more insidious – probably something you’re doing on the page. maybe a setting that’s shared between many stacks (like a Foundation/Foundry type thing).
Hope that helps out. If you do some of those experiments and still come out confused, put everything I need to see open the file (stacks, themes, etc.) and the project file together – zip them up – throw in on dropbox and send me a link. If you send it on my Slack channgel (http://slack.yourhead.com) I’ll probably get back to you pretty quick.