Hi Nick.
Yes, Andy is correct. If you don’t scale the image first (using the Histogram Transformation tool) the resulting JPEG file will show as a blank, black image. This also applies to TIFF format images which can be saved as both 16-bit and 32-bit files. Normal JPEGs are indeed only 8-bit but for posting online should be fine.
Cheers,
Nik
British Astronomical Association
Supporting amateur astronomers since 1890