Replacing the sky in a PSD file with a jpeg sky file.

Well I also had to Google who Barney is.  😁

I'll try not to get too excited about Glenn's distinction between a file type and an image type. 😋 I have no idea what he is referring to in this context and so I'm not sure how it would resolve any concerns you may have.

I don't know whether Barney will approve, but the simple answer to your question is that once a file in any compatible format is opened in the Editor, it is converted to PSD format.  You can insert a file in any format to the open file and it will become a new layer in the PSD file.  The jpeg file format does not support multiple layers.  So, if you replace a sky, using a jpg sky file as a new layer, the file cannot be saved as a jpeg unless you flatten the layers. If the file you open started off as a PSD file, it will remain in that format unless you choose to save the file in another format.  And if you try to save as a jpeg, you will be warned that your layers will be flattened.

Toss a jpg in any random psd file and you could find out for yourself.....

Think of PSD (Photo Shop Document) as a file type, not as image type and most of any concern should go away.

Now some folks are going to get all excitied and start talking about "psd is an image type, and it's wrong to blah blah blah."  Feel free to ignore all that, heck feel free to ignore what I'm saying right now. 

The working file, with all the layers,  included the jpg's can be a psd file (a file type) if you want it to be--- it pretty much must be, if you want to go back and edit that layer later in life. 



Barney style: do it. PSD files arent much more than a bunch of layers anyway, which can contain any number of image formats on the layers. .