BLOB Decoder
The BLOB decoder tool can decode Binary Large Objects (BLOBs) into the image or binary file they represent. BLOBs were added to GEDCOM 5.5 with the intention to allow multimedia files to be stored within the GEDCOM file. Use of BLOBs was depreciated when GEDCOM 5.5.1 was released.
Few applications write BLOBs and ever fewer can decode them. If you come across a file which contains BLOB data, it can be entered with or without tags and will be decoded into binary and hex forms. If the data is recognised as a valid image format, an image of the file will also be displayed. You can save the decoded data to a file name of your choice.
Fig 1. The BLOB decoder tool.
Supported BLOB formats
There are currently three known BLOB formats in use and all can be handled by the BLOB decoder tool.
GEDCOM: the original algorithm described in
Appendix E of the GEDCOM 5.5 specification.
The algorithm can cause data corruption if the original
binary data ends with 0xFF bytes.
GEDCOM (fixed): a corrected version of the original GEDCOM 5.5 algorithm which does not cause data corruption. This algorithm is used by GEDitCOM and The Complete Genealogy Builder.
Ancestral Quest: a
proprietary algorithm used only
by Ancestral Quest. This algorithm is based on the original GEDCOM 5.5
algorithm. The algorithm causes data corruption if
the original binary data ends with 0x00 bytes or its
length in bytes is not exactly divisible by 3.