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jpegrutils: set use_base_cg for Apple gain maps #484

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jpegrutils: set use_base_cg for Apple gain maps #484

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2ae3c54
jpegrutils: set use_base_cg for Apple gain maps
tejas-dbx-public Sep 23, 2026
5b2ce50
tests: round-trip Apple gain maps through the compressed-image encoder
tejas-dbx-public Sep 24, 2026
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3 changes: 3 additions & 0 deletions lib/src/jpegrutils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -729,6 +729,9 @@ uhdr_error_info_t getMetadataFromXMP(uint8_t* xmp_data, size_t xmp_size, uint8_t
metadata->offset_hdr[c] = 0.0f;
}
metadata->hdr_capacity_min = 1.0f;
// Apple applies the gain map in the base image's color space, and its gain-map
// image carries no ICC profile.
metadata->use_base_cg = true;

float max_content_boost;
bool present = false;
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36 changes: 36 additions & 0 deletions tests/jpegr_test.cpp
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Expand Up @@ -1753,6 +1753,42 @@ TEST(JpegRTest, decodeApple) {
}
EXPECT_EQ(gainmapMetadata->hdr_capacity_min, 1.0f);
EXPECT_FLOAT_EQ(gainmapMetadata->hdr_capacity_max, headroom);
EXPECT_TRUE(gainmapMetadata->use_base_cg);

// Re-encode the decoded base image, gain map and metadata (API-4). This must succeed as
// Apple gain-map images carry no ICC profile.
uhdr_mem_block_t* baseImg = uhdr_dec_get_base_image(dec);
ASSERT_NE(baseImg, nullptr);
uhdr_compressed_image_t baseCompressed{baseImg->data, baseImg->data_sz, baseImg->capacity,
UHDR_CG_UNSPECIFIED, UHDR_CT_UNSPECIFIED,
UHDR_CR_UNSPECIFIED};
uhdr_compressed_image_t gainmapCompressed{gainMapImg->data, gainMapImg->data_sz,
gainMapImg->capacity, UHDR_CG_UNSPECIFIED,
UHDR_CT_UNSPECIFIED, UHDR_CR_UNSPECIFIED};
uhdr_gainmap_metadata_t metadataCopy = *gainmapMetadata;

uhdr_codec_private_t* enc = uhdr_create_encoder();
ASSERT_NE(enc, nullptr);
uhdr_error_info_t status = uhdr_enc_set_compressed_image(enc, &baseCompressed, UHDR_BASE_IMG);
ASSERT_EQ(status.error_code, UHDR_CODEC_OK) << status.detail;
status = uhdr_enc_set_gainmap_image(enc, &gainmapCompressed, &metadataCopy);
ASSERT_EQ(status.error_code, UHDR_CODEC_OK) << status.detail;
status = uhdr_encode(enc);
ASSERT_EQ(status.error_code, UHDR_CODEC_OK) << status.detail;
uhdr_compressed_image_t* reencoded = uhdr_get_encoded_stream(enc);
ASSERT_NE(reencoded, nullptr);

uhdr_codec_private_t* dec2 = uhdr_create_decoder();
ASSERT_NE(dec2, nullptr);
ASSERT_EQ(uhdr_dec_set_image(dec2, reencoded).error_code, UHDR_CODEC_OK);
status = uhdr_decode(dec2);
ASSERT_EQ(status.error_code, UHDR_CODEC_OK) << status.detail;
const uhdr_gainmap_metadata_t* reencodedMetadata = uhdr_dec_get_gainmap_metadata(dec2);
ASSERT_NE(reencodedMetadata, nullptr);
EXPECT_FLOAT_EQ(reencodedMetadata->hdr_capacity_max, headroom);
EXPECT_TRUE(reencodedMetadata->use_base_cg);
uhdr_release_decoder(dec2);
uhdr_release_encoder(enc);

uhdr_release_decoder(dec);
}
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