photocraft/docs/sony-arw-metadata.md

Sony ARW metadata evidence

2026-10-11: PhotoCraft now reads applied white balance and black levels from Sony's encrypted SR2SubIFD when usable plain tags are absent. It also applies the measured ILCE-6000 image area. This corrects source metadata; it does not add a camera colour profile or a JPEG tone match.

Research and scope

PhotoCraft already contains the cRAW sensor decoder from #83 and the 512 black fallback from #1902. The open #2135 proposes fitting camera-JPEG colour and tone; #2230 adds camera profiles. Their actual bodies and diffs were reviewed before this change; neither is merged at the inspection date. This change addresses metadata missing from the existing decoder, without duplicating those colour-development proposals.

LightCraft's #115, #535 and its current camera-preview-colour documentation distinguish applied WB, camera calibration and JPEG tone/DRO. Its SR2 investigation suggested testing encrypted metadata before estimating WB from scene pixels. PhotoCraft's implementation is independent: no sibling source, decoder dependency or camera colour table is included. The first keystream words were recovered again from local metadata observations.

Measurement

Three read-only local ILCE-6000 ARW/JPEG pairs were inspected with ExifTool 13.59 and PhotoCraft's rawinfo example. No private files, scene pixels or metadata dumps are committed.

Source fact	All three ARWs
Sensor / output image	6048 × 4024 / 6000 × 4000
cRAW code range after SonyToneCurve	14-bit; white 16383
SR2SubIFD BlackLevel (0x7310)	512, 512, 512, 512
Applied WB_RGGBLevels (0x7313)	2764, 1024, 1024, 1784
Applied R/G/B multipliers	2.69921875, 1, 1.7421875
Image area observation	[12, 12, 6012, 4012], corroborated by EXIF dimensions and JPEG framing

Previously WB was estimated independently from each scene, yielding R/G/B gains of roughly 2.920/1/2.214, 2.661/1/1.823 and 3.063/1/1.645. All three now use the camera's applied gains. The measured crop is specific to ILCE-6000 at this sensor size; an explicit existing crop wins. Other models and sensor sizes are unaffected by that entry.

The pinned public-domain DSC-RX0 corpus sample independently verifies black 800 in all four positions, rather than the former 512 fallback, and WB 2056/1024, 1, 1908/1024.

Container and safety

Tag meanings come from ExifTool's public Sony tag documentation. IFD0's 50740 BYTE/UNDEFINED[4] points to SR2Private, whose 0x7200, 0x7201 and 0x7221 provide the block offset, byte length and key bytes. Only the observed 11 22 33 44 key is supported. XOR of ciphertext with black-box decrypted metadata yielded the same first 127 big-endian keystream words for all three files. Every subsequent whole word in each 56958-byte block obeyed k[n] = k[n-63] XOR k[n-127]; the incomplete final word is stored in the clear.

Only four SHORT/SSHORT values for 0x7310 and 0x7313 are read. Their absolute value offsets must resolve inside the decrypted block. Allocation is capped at 1 MiB and Limits.max_alloc; the whole directory and source bytes must exist. Negative or excessive levels, unusable gains, other keys and malformed metadata are ignored, retaining the existing decode and fallback. Usable plain tags take precedence; invalid plain WB does not conceal valid encrypted WB. Auto-WB fields and unverified Tag2010 layouts are not substituted for applied WB.

Synthetic tests cover both byte orders, offsets beyond the first recurrence period, fixed keystream observations, an incomplete final word, precedence, invalid levels and gains, every truncation of a procedural fixture, out-of-block offsets, absurd sizes and allocation limits. The public RAW corpus pins the RX0 metadata and checks deterministic 16-bit development.

Rendering limits

The full sensor buffer still passes through black subtraction, applied WB, demosaicing and 16-bit ProPhoto-compatible development. The embedded JPEG remains a comparison image; it is not substituted for RAW pixels. All three files import and export at 6000 × 4000 in 16-bit RGB.

Local comparisons with the paired camera JPEGs and installed LightCraft 0.6.0 show reduced WB casts, but PhotoCraft remains flatter, darker and less saturated. These ARWs have no DNG colour matrix, so the existing neutral camera-to-sRGB fallback and scene-referred tone remain. Camera JPEGs also have DRO Auto and lens/tone processing; they are visual references, not linear sensor oracles. The remaining camera colour and tone work belongs to G14 and the open colour/profile proposals above. Three uncontrolled scenes do not establish a camera calibration.