Fix: XML serializer corrupts zero header colour-space signature on round-trip (#1355)#1356
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xsscx merged 1 commit intoJun 15, 2026
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…und-trip (InternationalColorConsortium#1355) CIccProfileXml::ToXml() wrote the data colour space and PCS header signatures via icGetColorSigStr() unconditionally. For a zero signature (0x00000000) that helper returns the literal text "NULL"; the inverse icGetSigVal("NULL") on reparse packs the ASCII bytes 'N','U','L','L' into 0x4E554C4C, so a NoData header silently became "Unknown 'NULL' = 4E554C4C" after a ToXml -> FromXml round-trip. The JSON serializer (IccProfileJson.cpp:136-137) already guards both fields, emitting "" for a zero signature, which round-trips back to 0 -> "NoData". This is the sole reason iccFromXml and iccFromJson reported different data colour spaces for the same profile (InternationalColorConsortium#1355). Mirror the JSON behaviour: emit an empty element for a zero DataColourSpace / PCS signature. icXmlGetChildSigVal() returns 0 for an empty element, so the value round-trips faithfully. A zero data colour space is itself invalid for a v2/v4 profile per ICC.1 (v4.4.0.0) 7.2.6 / Table 19; preserving the bytes is a serialization concern, leaving the validator to flag the malformance. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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This was referenced Jun 15, 2026
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This was referenced Jun 15, 2026
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Summary
Closes the FromXml/FromJson divergence reported in #1355.
CIccProfileXml::ToXml()serialized the data colour space and PCS header signatures withicGetColorSigStr()unconditionally. For a zero signature (0x00000000) that helper returns the literal textNULL, and the inverseicGetSigVal("NULL")on reparse packs the ASCII bytesN,U,L,Linto0x4E554C4C. ANoDataheader therefore becameUnknown 'NULL' = 4E554C4Cafter aToXml -> FromXmlround-trip.The JSON serializer already guards both fields (
IccProfileJson.cpp:136-137), emitting""for a zero signature, which round-trips back to0->NoData. That guard is the entire reasoniccFromXmlandiccFromJsonreported different data colour spaces for the same profile.Fix
Mirror the JSON behaviour in
IccProfileXml.cpp: emit an empty element for a zeroDataColourSpace/PCSsignature.icXmlGetChildSigVal()already returns0for an empty element, so the value round-trips faithfully.(same guard applied to
<PCS>)Verification
Repro profile:
Testing/hybrid/Results/LCDDisplayCat8Obs.icc(emitted byiccV5DspObsToV4Dsp, header data colour space =NoData/0x00000000).iccToXmlelement<DataColourSpace>NULL</DataColourSpace><DataColourSpace></DataColourSpace>iccFromXmlre-dumpUnknown 'NULL' = 4E554C4CNoDataiccFromJsonre-dump (unchanged)NoDataNoDataRGB/XYZand round-trips intact (no regression).Scope / spec note
A zero data colour space is itself invalid for a v2/v4 profile per ICC.1 (v4.4.0.0) §7.2.6 / Table 19 — this PR does not try to "correct" the malformed profile, only to stop the serializer from corrupting the bytes. Faithful preservation is a serializer concern; flagging the malformance is the validator's job. See the analysis on #1355 for the full spec discussion (including the
"NoData"descriptor and the colorant-tag classification, both tracked separately).A paired regression test PR will follow per the established fix/test split (cf. #1344/#1345).
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