Like it says a web downloaded .jpg file that is 333KB to 15.6MB on a 4x upscale with no conversion selected. Is it normal for the file size to be so big? Is it adding that much information?
It may well be, depending on the detail in the input file, as output is 100% in GigaPixel so full resolution with no loss.
You can choose the quality level of the output JPEG in the File Format settings. The “Maximum” setting will be similar in size to a TIFF. The “High” setting is equivalent to JPEG quality level 8 (or 80%) that many programs default to and should be quite a bit smaller.
