Unless you're really a whiz at Photoshop, chances are that you'll go through several edited versions of a photograph before you arrive at just the version you're after. I often spend hours (even days) on a really important image and create a dozen or more different interpretations.
One thing you have to be careful of though is not saving the new versions with the same file name as the old one; if you do, of course, you erase the previous version. While that might not seem to matter if you like the new version more, the fact is that in the cold light of day, you may actually prefer earlier versions. All it takes is a little bit of organization (and some hard drive space) to save each different version until you're sure you have the one you want.
I've played with this shot of the Camden, Maine harbor many times (the shot is simply too crowded, but I keep playing with exposure and color balance to try and improve it--silly, I know) and each time I do I change the file name slightly: "Camden_Harbor 1" "Camden_Harbor 2," etc. That way I can always go back and look at earlier takes. I also keep the layers open when I save "working" images because that way I can trace exactly what I did and also turn various layers on or off at will. Finally, when I'm sure I have a file I like, I flatten the image, choose a final name and save it to a "finals" folder.
One other reason to change file names slightly is that if you open and re-save jpeg files (and only jpegs--it's OK to save TIFF or PSD files with the same name--though you will, of course, still delete the earlier version if you do) using the same exact file name, you degrade the file! Yes, you are actually harming the file each time you open and resave it under the same name--so don't do it!
Organization is an important thing in image editing, especially when, as I do, you have tens of thousands of digital files. So come up with a good naming scheme early and stick with it--you'll be glad you did.
Tracy Arm Fog
2 days ago