How IDimager stores Meta information
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Some formats allow embedded storage of meta information, which means that the descriptive information will be stored inside the image file itself. Generally this is the best way of storing meta information, because you are ensured that the information travels with your image file and you that won't have to fully depend on the catalog database.
File formats that allow embedded storage of meta information include: PSD, JPG, TIFF, CRW (through THM) and DNG. Some other RAW formats, such as NEF, CR2, PEF and ORF, allow storing meta information to the file itself, but some RAW converters will fail to work once the original RAW file is altered. To preserve maximum interoperability, IDimager is configured by default not to embed meta information in RAW files; to enable storing meta information to RAW files, change the setting in the options dialog (Tools | Options | General | Allow embedded meta writing for RAW files). However, it is strongly recommended that you first experiment on a copy of a RAW file to confirm that your RAW converter and other third party tools are able to handle altered RAW files.
Some image formats, such as BMP, GIF, ICO, etc., do not allow you to write embedded meta information. For these formats a "sidecar" file is created that holds the meta information. This sidecar file has the same base name as the original file but uses a different extension: .xmp. For example: if you are working with a BMP file named "Sample.bmp", meta information for this file will be stored in a sidecar file named “Sample.xmp”.
IDimager will always keep the XMP sidecar file together with your original file, so when you move the image using IDimager, IDimager will move the xmp file with it. Likewise if you copy the original file, IDimager will copy the xmp file at the same time. In general, if an xmp sidecar file exists, the sidecar will be used by IDimager.
Apart from non-embedded formats, IDimager will also create XMP sidecar files for read-only files, even if these images are formats that allow embedded XMP. This allows IDimager to store metadata for the image to the filesystem, even though IDimager can not write to the image file. Unfortunately, many third party applications will not read fhe XMP from sidecar files for formats that support embedded XMP, so please keep IDimager's behavior in mind when deciding whether or not to work with read-only files.
In summary, meta information is stored either as embedded XMP or as an XMP sidecar file. In addition, for file formats that support embedded IPTC records (JPG, TIFF, etc.), IDimager will map all relevant meta information into this format and store the appropriate fields. Likewise, if the file format supports EXIF records, IDimager will map all relevant information into this format as well and store it in the appropriate fields. In this way, you'll have maximum compatibility with other tools, even if these other tools don't support XMP.
Finally, IDimager stores all XMP information to its own database. This allows you to search in your catalog for images that contain specific meta information, regardless of whether those images are online or offline (e.g. you can locate images stored on a DVD that match a certain condition, even if the DVD is not in the drive).