DNG (Adobe Digital Negative)

DNG is Adobe’s vendor-neutral container for camera RAW files. iPhone ProRAW writes DNG. Android’s “RAW” mode writes DNG. Leica, Hasselblad, Pentax, and Sigma ship DNG natively. Even when shooting CR3 / ARW / NEF, Adobe Lightroom converts to DNG on import for archival workflows.

Mechanically, DNG is TIFF with extra tags — same IFD-based file structure, same byte-order quirks, processed by the same handler in Tracemute. The interesting part is what DNG-specific tags carry, and which of those leak device identity.

What it carries

Everything TIFF carries (Make, Model, Software, DateTime, Artist, Copyright, ExifIFD, GPSIFD, XMP, MakerNote), plus DNG-specific tags many of which are RAW-processing-essential:

• 0xC621 ColorMatrix1 / 0xC622 ColorMatrix2 — XYZ-to-camera-sensor colour matrices, per illuminant. Required to correctly interpret RAW sensor values.
• 0xC627 AnalogBalance / 0xC628 AsShotNeutral — white-balance state at capture.
• 0xC628 BaselineExposure / 0xC62B BaselineNoise / 0xC62C BaselineSharpness — per-camera-profile baseline values.
• 0xC61A BlackLevel / 0xC61D WhiteLevel — sensor reference values.
• 0xC68F AsShotICCProfile / 0xC690 AsShotPreProfileMatrix — embedded ICC profile chain.
• 0xC6D2 OpcodeList1..0xC6D4 OpcodeList3 — pixel-correction opcodes applied by the RAW processor.

And the DNG-specific identifying tags that Tracemute drops:

• 0xC614 UniqueCameraModel — body class identifier, often more precise than “Make/Model” (e.g. distinguishes camera firmware revisions).
• 0xC615 LocalizedCameraModel — localised display name.
• 0xC68B OriginalRawFileName / 0xC68C OriginalRawFileData — the original camera RAW filename, often including the body serial number embedded in the path.
• 0xC6F3 CameraCalibrationSignature / 0xC6F4 ProfileCalibrationSignature — per-body calibration fingerprints.
• 0xC7A1 CameraSerialNumber — explicit body serial number.

What’s unique

DNG’s identifying surface is larger than TIFF’s because of the calibration-signature tags. Two Lightroom-exported DNGs from the same camera body have the same CameraCalibrationSignature even if every other piece of metadata has been scrubbed — that’s enough to link photo sets across years of edits.

DNG also frequently puts the primary image data in a SubIFD (referenced by tag 0x014A in IFD0) while IFD0 holds a smaller thumbnail. The strip has to recurse into the SubIFD and rewrite both — dropping metadata in just IFD0 would leave the full image’s metadata intact.

What Tracemute does

The same handler as TIFF, invoked with outputMime: image/x-adobe-dng:

1. Parse the TIFF header.
2. Walk IFD0 + every SubIFD it references.
3. Drop all identifying TIFF tags (Make, Model, Software, DateTime, Artist, Copyright, ExifIFD, GPSIFD, MakerNote, XMP, IPTC) and the identifying DNG-specific tags (UniqueCameraModel, LocalizedCameraModel, OriginalRawFileName, OriginalRawFileData, CameraCalibrationSignature, ProfileCalibrationSignature, CameraSerialNumber).
4. Keep every DNG colour-calibration tag (ColorMatrix1/2, ForwardMatrix1/2, AnalogBalance, AsShotNeutral, baseline exposure/noise/sharpness, OpcodeList1/2/3, ProfileToneCurve, calibration illuminants) so the cleaned file still processes correctly in Lightroom, Camera Raw, darktable, RawTherapee, etc.
5. Patch StripOffsets / TileOffsets / SubIFDs pointers to the new positions. Copy raw sensor data verbatim.

What survives

Every byte of the RAW sensor data. Every colour-calibration matrix. The ICC profile. The structural TIFF tags every DNG reader requires. The DNGVersion / DNGBackwardVersion declarations.

What does NOT survive: anything that could link the file back to a specific camera body, a specific edit session, or a specific shoot. The cleaned DNG opens cleanly in any RAW processor — just without “this file came from body serial XYZ123.”