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Problem
imaging's ICC parser (prism/meta/icc) rejected Gray colorspace profiles: the header validator only allowed RGB/CMYK, and the matrix/TRC transformer builder only knew how to build RGB (3-curve + colorant matrix) pipelines. Sinceautometa.Loadparses ICC metadata before pixel decoding, any Gray-profile image would fail. You can check the problem with this image: https://www.wikidata.org/wiki/Q54883642#/media/File:Paloma-S%C3%A1nchez-Garnica.jpgChanges
profilereader.go: acceptColorSpaceGrayin header validation.tagtable.go: addedload_media_white_point()to read thewtpttag (also reused byget_effective_chromatic_adaption).pcs.go: addedGrayToXYZ/XYZToGraytransformer types implementing the ICC monochrome matrix/TRC model — an achromatic value is scaled by the media white point to produce (or is recovered from) PCS XYZ.profile.go:create_matrix_trc_transformernow delegates to a newcreate_gray_trc_transformerfor Gray profiles, using thekTRCcurve plus white-point scaling instead of the RGB colorant matrix.profile_gray_test.go: new test building a synthetic Gray ICC profile (parametric gammakTRC+wtpt) and verifying decode + round-trip gray → PCS → gray.