We require level 10 JPEG files to be sent to us. We use JPEG’s because the compression is a very efficient image compression algorithm designed specifically for saving photographic images. It takes advantage of how we see color versus brightness to only save information needed to reproduce the image for people to view. Image data is lost during compression but at high levels of quality you will not see a difference between a level 10 JPEG and a Tiff printed to paper.
JPEG compression
is perfect for transient files for sending to the lab for printing, but
avoid using the compression as a working file type. Also avoid opening a
JPEG, making changes, and resaving it again as a JPEG repeatedly. If
your workflow calls for this to happen, save your files as Tiff or PSD
files until they are complete and ready for output. Any JPEG artifacts
you see in your prints come from the JPEG file coming out of your
camera, not from saving them as a level 10 for output purposes.