You can do it, but it is a bit clunky. LR for some reason does not permit you to save the XML sidecar for virtual copies of a"master" raw file. You can CMD-S (CTRL-S on PC) while in the Library module to save the sidecar for a raw file. If you create a Virtual Copy of that raw, you can make edits, but you cannot save a unique sidecar for that VC. There is a work-around, however. You can select the VC as the new Master, from the Photo menu:
Photo > Set copy as Master
Now you can CMD-S and save the sidecar for the VC, now designated as the Master.
Here's what I tried:
1) Make a VC of your raw.
2) Make your adjustments to the raw (if you desire) and save the sidecar (CMD-S).
3) Copy that sidecar into a directory that is not where the raw currently resides.
4) Make your adjustments to the VC.
5) Designate it the new Master and CMD-S to save the sidecar for the VC.
Now you have two sidecar files, but they are named identically. You need to change one of them so that you can differentiate between the two. Let's say you name them:
original.xmp
vc.xmp
Now you have a human readable XML snapshot of both settings. You can use any number of tools to compare and point out the differences between the two files. Word has the "Compare Documents" operation, etc.
The simplest way is to use the "diff" command line tool (at least for the Mac Terminal):
diff original.xmp vc.xmp > difference.txt
will compare the two documents and write the differences to a text file, here called "difference.txt."
There are probably multiple ways to accomplish this same thing. My understanding is that LR writes the sidecar for the original raw, but writes the VC settings to the LR database. Who knows why this is the preferred way, but if you need to do this for only a few images, it may work. If you have a lot of images on which to perform this task, well ... good luck!
You also may want to look into LR Snapshots, but I honestly do not use LR very much, so I cannot help you there. Apparently each snapshot (which is just a text list of the collection of settings for the image state when you make the snapshot) is stored in the XML sidecar for that image. This way, instead of making virtual copies, you could make several snapshots on the image as you progress through various renderings for that image. When you save (CMD-S) the sidecar, it will contain ALL of the snapshots and the settings for each one. Problem is, you will have to go through the XML and find each section in the XML where a new snapshot exists and compare that section of XML to another. There are probably XML parsers that will make this easier, either comparing sections of XML in a single file or breaking out each snapshot section of XML into a new text file for comparison.
Maybe someone else can chime in.
kirk
