Lightroom is an image management tool (database) and a file processor. This means it can manage your images for you allowing more efficient filing and retrieval of images as well as defining the parameters to use to process raw and other files for export either into an editor like Photoshop or a final file for printing or sharing. By defining parameters I mean that Lightroom writes data to a file that tells the processor what to do to that file on export. It does not directly modify the file – it creates instructions on how to modify the file. That is the database part, along with remembering where files are located.
Think of Lightroom as a library card catalog. The card catalog does not contain the books, but references to where the books can be found. Lightroom references where your files can be found on a hard drive. The Lightroom catalog is metadata; information about other data, which is your image file. Initially, the information is location of the file, resolution, color space, copyright, keywords, etc. As you process an image, more data is written to the catalog as instructions on how to process your image. I suggest you also set preferences to export settings to an XMP sidecar file. This copies the processing, ratings and other information to a file that accompanies the raw file in your hard drive and gives you an additional measure of backup, and the ability to open the file with modifications intact in Bridge or ACR.
If you modify a file outside of Lightroom the XMP file for that file will contain the changes, but Lightroom will not automatically update the database to reflect those changes. An icon will appear in LR (up arrow with lines at top right) indicating that the XMP file has changed. Click on the icon and you will be asked whether to import the modifications from the XMP file or not.
I will be presenting a 3 hour seminar on Lightroom next Saturday, March 11, 2017 at the Hershey Library starting at 9:30 a.m. You will need to sign up through the library. Sign up for the seminar at the Hershey Library. The cost is $45.
I will be presenting a Photoshop seminar at the Hershey Library on April 29th (same time, same channel). Hope to see you.