Research: 6-channel MinIsBlack TIFF files omit the `ExtraSamples` tag

[xsscx]

Research

2026-09-03 20:25:37 UTC

Task

Research why 6-channel MinIsBlack TIFF files omit the ExtraSamples tag

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[xsscx]

Codex Report

2026-09-03 20:29:40 UTC

1. Spectral TIFF carrier convention

The 81-channel source and generated 36-channel MinIsBlack TIFF files omit the
ExtraSamples tag. TIFF 6.0 requires that tag when SamplesPerPixel exceeds the
components implied by PhotometricInterpretation. libtiff repairs the directory
in memory and prints:

Sum of Photometric type-related color channels and ExtraSamples doesn't match SamplesPerPixel. Defining non-color channels as ExtraSamples.

Do not silently choose semantics in code. First determine and document the ICS
carrier contract:

• use ExtraSamples=0 for every spectral band after the first; or
• define and cite an approved spectral TIFF convention.

TIFF itself does not associate samples with wavelengths. The embedded iccMAX
profile supplies the 81-channel identity, spectral type, range, and step count.

2. ICS profile diagnostics

The image workflow finishes, but the generated full profile is reported
noncompliant by iccDEV:

• v5 minor version is reported unexpected;
• observer CMF is reported missing;
• illuminant SPD is reported missing.

Keep this separate from TIFF transport correctness. Do not report the ICS as a
full conformance PASS until these diagnostics are resolved or normatively
explained.

3. sameAsSource boolean conversion

In iccApplyProfiles.cpp, these expressions convert TIFF enum values directly
to bool:

SrcImg.GetCompress()
SrcImg.GetPlanar()

This is wrong because COMPRESSION_NONE and PLANARCONFIG_CONTIG are both
nonzero. A sameAsSource request can therefore change uncompressed to LZW and
contiguous to separated. Add exact enum comparisons and focused JSON config
regressions.

4. Decoded strip byte count

ReadLine() tests TIFFReadEncodedStrip() only for a negative result. The API
returns the actual decoded byte count. Validate that the returned count covers
the rows that will be copied, particularly a short final strip, rather than
allowing reads from uninitialized buffer space.

5. Explicit capability and error checks

• Reject tiled input explicitly or implement a tile path.
• Validate every required TIFFSetField result.
• Consider TIFFOpenExt allocation limits and per-handle warning handlers.
• Replace manual planar strip arithmetic with TIFFComputeStrip and
  TIFFNumberOfStrips where practical.
• Keep size calculations in size_t, tmsize_t, or checked 64-bit types until
  the API boundary.
• State the current first-IFD, top-left orientation, 8/16/32-bit, strip-only,
  and classic-TIFF output limitations in tool documentation.