JPEG Quantisation Table
Definition
A matrix of 64 values embedded in a JPEG file that controls the precision with which each frequency component of the image is encoded. Camera manufacturers and software applications use distinct quantisation table sets; matching a file's tables against a known-camera database is a core technique for identifying the encoding device or application.
- Size
- 64 values, an 8 by 8 matrix
- Location
- Embedded in the JPEG file header
- Forensic use
- Identifying the encoding device or software
- Method
- Matching against a known-camera table database
Common questions
Why do quantisation tables differ between devices?+
Manufacturers and software encoders tune the table for their own balance of image quality against file size, so the specific values act like a fingerprint of the encoder used to produce the file.
What happens to the table when an image is re-saved by different software?+
Re-saving replaces the original table with the new encoder's own table, which is exactly what lets an analyst detect that an image was processed or re-saved after its original capture.
Related terms
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- PNG Chunk
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- Thumbnail Inconsistency
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- XMP (Extensible Metadata Platform)
- An Adobe-defined metadata format stored as an XML packet embedded in image files. XMP carries a software history field (xmpMM:History) that editing...