If things are as equal as possible there shouldn't be such a significant difference between a jpg file from the print module and a jpg from the Library module. Assuming the original file is a raw file, export a jpg with dimensions of 800 pixels on the long edge (should give you and 800x600 image based on 35mm format) Apply no sharpening, no keywords and leave Metadata set to All. Then take the same image into the print module and print as jpg with Custom File Dimensions of 8in x6in and a File resolution of 100ppi. Again apply no sharpening. In the finder there may be a small difference in weight of the file. In my case 370kb from Library and 340kb from Print. Open the files in Photoshop and you should see practically no difference in image quality and if you invoke the Image Size dialog both files should be identical dimensions and Image Size (mb) The difference in the finder record weights can be attributed to the metadata or RAW data inside the file. View the file in Photoshop and invoke the file info . File > File Info... You'll see a large difference in the amount of data located in the RawData section. So, to get a significant difference between files exported from the Library Module and the Print Module you will be changing compression specs (jpg quality) and sharpening specs. I know of no benefits to printing a jpg versus exporting a jpg assuming no borders or overlays are required.
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