I recently purchased the Nikon D50 and am very new to Photoshop. The ither day I downloaded a JPEG fro my D50 and did some post-processing in Photoshop CS. I noticed that when I use "SAVE AS", I can save to a JPEG format but if I use "SAVE", I cannot choose JPEG but there is a PSD format. I also noticed that the JPEG is 856KB but the PSD is 81,879KB. What is the PSD format used for?
Also, when I use "SAVE AS" and save it to JPEG, I get the following options:
Image Options -> Quality -> 10 Maximum
Format Options -> Progressive -> Scans -> 3
Size -> 56.6kps
What do these numbers / options mean?