I'm creating a poster that is 50cm x 70cm at 300dpi. The empty document is 5.1M when saved... which still seems ridiculous for a completely empty white document, but I can live with it.
When I place a linked 4.3M JPEG image (File -> Place Linked...) and save, the PSD balloons to 95.5M. Nothing else, just a 4.5M JPEG linked in an empty document.
This seems completely absurd... the file is under 5M and it shouldn't even be including it, and when the JPEG is opened in Photoshop itself it's full in-memory size is only 34.9M.
How is it managing to waste all this space? How can I prevent it from doing so?
I've already tried:
I'm using Photoshop CC 2015.05.0 on OSX 10.10.5.
It's pretty obvious that Photoshop is saving a version of the linked file in the PSD: if I delete the linked file and open the PSD I can still see the image in the document. What I am looking for is a way to disable this behavior so that it does not include that information from the linked file (I don't care about it showing up if the source file is missing).
Although your file is linked, Photoshop still saves the flattened image data. With a JPG you are unlikely to see any file size savings by using linked files. If you link another layered PSD for example, you will see file savings since all it is saving is the flattened pixel output and nothing else.
The pixel preview it saves is scaled to its current size, so if you link a higher resolution image and scale it down it will only save the preview at the scaled down size, potentially giving you some file size reduction. But again, if it is a flat JPG your unlikely to save much on the original file size unless it is significantly scaled down. And if you're scaling your image up you're likely to add even more to the file size.
While Linked Smart Objects do not store the original file in the containing document, they still store a flattened and scaled version of the image data from the original file. In some cases, the size of this data may be much larger than the size of the original file
It's also worth noting that JPG is a compressed output format, simply opening a JPG in Photoshop as a PSD increases the file size significantly.
Put a solid color layer on top of all layers. This layer must be visible before you save and close the file. With this trick, you can achieve 46% file size reduction.