A Photoshop History Lesson
Yes, Version 1.0 of Photoshop shipped in February of 1990, but that's not what this week's PhotoTip article is about. No, not that kind of history. Instead, we're going to take a look at the History Log option available in Photoshop CS and CS2. If you haven't discovered it yet, you should.
You probably are already familiar with the History Palette. Every editing change you make to an image in Photoshop creates a new History Palette entry or "state." To go back to what your image looked like at any given point you can click on that state in the History Palette to undo everything that came after. But the History Palette does have limits, most notably the fact that it goes away when you close an image. You start over with a brand new empty History Palette when you next open that image. If you want to know what you did last time, you'd better have kept track of your editing steps some other way because the History Palette can't be saved.
Thankfully, you don't have to deal with writing everything down yourself since Adobe thoughtfully provided the History Log option. By default, it's not turned on, but you can easily enable it in Photoshop's Preferences dialog. To do so, go to Edit >> Preferences >> General if you are a Windows user, or the same thing under the Photoshop menu if you use Mac OS. Click on the History Log checkbox at the bottom of the General tab.
The Preferences for the Photoshop History Log
You have a choice of saving the log individually embedded in the metadata of each image, in a common text file shared by all images, or both. If you choose to embed it in each image, you will be able to see on the File Info dialog.
You can also choose what level of detail you want to record. Sessions records only the time you open, close or save an image. Concise records these times as well but also includes a list of each change you made as it is listed in the History Palette. Detailed adds a record of the settings used by each editing step and also includes the full path to the file in your file system rather than just the file name. If you bill clients for your time but don't need any other information, the Sessions log can be a big help. If you want more than just this, I'd suggest going for the Detailed option. The Concise version really doesn't give you enough to go on if you need to remember what you did.
Here's an example showing both the Consise and Detailed History Log that resulted from selecting a portion of an image with the Lasso tool and applying an Unsharp Mask:
Set Selection To: polygon
Points: point list
point: 819 pixels, 258 pixels
point: 819 pixels, 258 pixels
point: 815.3 pixels, 260.5 pixels
point: 814.7 pixels, 261.7 pixels
point: 814.5 pixels, 262.1 pixels
point: 814.3 pixels, 262.5 pixels
Feather: 50 pixels
Unsharp Mask Amount: 194%
Radius: 13.7 pixels
If you spend much time on an image, the Detailed version can get pretty long, but compared to the size of an average Photoshop PSD file, it isn't much at all. An average editing step might require 100 bytes of data to record, so it would take over 10,000 entries to equal a megabyte. An image saved from my Nikon D2x as a 16-bit PSD takes 80 MB even without any added adjustment layers so the space needed for the extra information is insignificant.
If you save the History Log as metadata, you may be wondering how you can get rid of it if you do later decide you don't want it for some reason. If you go to the Advanced tab of the File Info dialog, you will find and expandable structure showing all the XMP metadata the file contains including the History Log. To find it, click on the plus sign next to the line labeled "Adobe Photoshop Properties" and you should see a line titled "Photoshop:History." This is it. To delete it, highlight the History line and click on the Delete button at the bottom of the window.
The History Log saved as embedded metadata as seen in the File Info dialog
You can also save the History Log to a file along with all the rest of the metadata using the "Save..." button in the Advanced tab of File Info, but if you do you may find it a bit challenging turning it into a readable form since the file will be in XML format.
At some point, you've probably looked at an image you spent a fair amount of time working on in Photoshop and wished you had taken better notes along the way so you could do whatever it was again on another image. At least I know I have. There may be no easy answer what we've already done, but at least the History Log gives us an answer going forward. This way, you can focus on being creative rather than on worrying about taking notes.