Tutorial : Metadata for photos

[michel038]

This is a translation of a french version : viewtopic.php?p=170164#p170164
Metadata
Metadata can be added to photos to facilitate their management.
There are basically three families, from the oldest to the most recent: EXIF, IPTC, XMP.
The EXIF metadata are now reserved for technical information, it is logical not to modify them except for the dates and GPS coordinates which can be created or modified if necessary, using the menu "Tools, Change timestamp" or "Tools, Metadata, Edit GPS data".
You can add a lot of information to describe, qualify, or organize and sort the photos, in IPTC or XMP metadata.
The XMP standard is tending to replace IPTC, but one can continue to use these two families simultaneously.
The "JPG" image format and some others pictures formats support metadata embedded in the image file itself.
But other formats only support certain kinds of metadata, for example ( Most of ) the "raw" formats only support external XMP metadata, put in a companion file next to the image file.

Keywords, categories, catalog
Keywords are metadata like any other, but XnViewMP has a specific tool called "Categories" to ease their management.
This tool also manages a database, "the catalog".
I use the term "assign categories to photos" to describe the action of linking a photo, a category and the corresponding keyword, which is done by simply checking a category box in the "Categories" panel while photos are selected.
In order for the "Categories" tool to write the keywords in IPTC or XMP format, you must have previously validated the corresponding export options in the "Settings, Metadata" screen, otherwise only the "catalog" contains the categories linked to the photos, (in which case it is advisable to regularly make backup copies of the catalog, simply by copying the xnview.db file after quitting XnViewMP).
Note: it is necessary to deselect the photos after checking the category boxes
There is a parallel between "categories" and "keywords": categories refer to the XnViewMP catalog and correspond to the keywords written in the photos when an export option had been validated.
There are two other metadata managed like the keywords: the "Star Ratings" and the "Color Labels". This information is also stored in the catalog, and has its own export options in the same options screen, "Settings, Metadata" (available only in XMP)

Other metadata
The other metadata managed by XnViewMP are quite numerous; There are for example Caption, Title, Author, Credits, Locations ...
This other information can also be written in the IPTC group and in the XMP group
To write these metadata, select photos then open the window "Tools, Metadata, Edit IPTC" (or Ctrl I). First you have to choose if you want to write "IPTC only" or "IPTC + XMP" in the "Mode" box of the last tab. Then go through the other tabs and enter information in the boxes, then click the write button so that this data is written in the photos. In fact, only the "Caption" and "Source" tabs contain fields commonly used by amateur photographers.
Users with specific needs for using XMP metadata can instead use the "Edit XMP" window, which works similarly. One can also use the companion XMP files by having checked this option in "Settings, Metadata".
These various metadata are not managed in the XnViewMP catalog, but only written (or read) in the photos, which should make you want to make backup copies of your photos if you were not already convinced of this necessity.

Using Metadata
XnViewMP offers several ways to take advantage of the metadata you have added to your photos
- The "Category Filter" panel allows you to find photos with a specific category. We can also say that the category filter allows you to find photos containing a certain keyword. It is an extremely efficient tool if you have filled in your photos with well-chosen keywords (categories), and possibly ratings (1 to 5 stars) or colors.
With the Ctrl key you can select several categories, and with the Alt key you can exclude categories.
- The "Quick Search" box in the toolbar. This box allows you to quickly find a photo based on a criterion, but only among the photos currently displayed.
(Remember that you can use "View, Show files in subfolders)
The options are in "Settings, Explorer, Quick search" (check at least IPTC and Catalog), This search is also about file names.
- The "Search" function in the Tools menu. This function is very rich, but searches for information in the catalog are much faster than searches for other metadata.
- There are also many methods of sorting and filtering photos.
All these methods make thematic sorting and storage of photos unnecessary. They also allow automatic display of captions (or labels or titles...)
One should not confuse the storage of photos which can be simply chronological, and the search or selection of photos which will be based on metadata, in particular keywords.

IPTC and XMP metadata are normalised, so other softwares will be able to take advantage of metadata you'll have entered in photos.

( Edited 2023 03 14 after Buckskin information below. Thank you )

[BuckSkin]

"raw" formats only support external XMP metadata, put in a companion file next to the image file.

Thanks for this informative tutorial; much needed and much appreciated.

While it probably stands true that most RAW formats will not accept XMP data internally, I have been using both ExifToolGUI and XnViewMP to successfully write numerous fields of both IPTC and XMP internally within my Canon CR2 RAW image files generated from several different Canon models; no sidecars.

jpegs created from these RAW files contain and display all of this data.