90 lines
2.9 KiB
C++
90 lines
2.9 KiB
C++
// Copyright (c) the JPEG XL Project Authors. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#ifndef LIB_JXL_BASE_EXIF_H_
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#define LIB_JXL_BASE_EXIF_H_
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// Basic parsing of Exif (just enough for the render-impacting things
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// like orientation)
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#include <jxl/codestream_header.h>
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#include <cstddef>
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#include <cstdint>
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#include <vector>
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#include "lib/jxl/base/byte_order.h"
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#include "lib/jxl/base/compiler_specific.h"
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namespace jxl {
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constexpr uint16_t kExifOrientationTag = 274;
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// Checks if a blob looks like Exif, and if so, sets bigendian
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// according to the tiff endianness
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JXL_INLINE bool IsExif(const std::vector<uint8_t>& exif, bool* bigendian) {
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if (exif.size() < 12) return false; // not enough bytes for a valid exif blob
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const uint8_t* t = exif.data();
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if (LoadLE32(t) == 0x2A004D4D) {
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*bigendian = true;
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return true;
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} else if (LoadLE32(t) == 0x002A4949) {
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*bigendian = false;
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return true;
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}
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return false; // not a valid tiff header
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}
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// Finds the position of an Exif tag, or 0 if it is not found
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JXL_INLINE size_t FindExifTagPosition(const std::vector<uint8_t>& exif,
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uint16_t tagname) {
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bool bigendian;
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if (!IsExif(exif, &bigendian)) return 0;
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const uint8_t* t = exif.data() + 4;
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uint64_t offset = (bigendian ? LoadBE32(t) : LoadLE32(t));
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if (exif.size() < 12 + offset + 2 || offset < 8) return 0;
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t += offset - 4;
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if (offset + 2 >= exif.size()) return 0;
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uint16_t nb_tags = (bigendian ? LoadBE16(t) : LoadLE16(t));
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t += 2;
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while (nb_tags > 0) {
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if (t + 12 >= exif.data() + exif.size()) return 0;
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uint16_t tag = (bigendian ? LoadBE16(t) : LoadLE16(t));
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t += 2;
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if (tag == tagname) return static_cast<size_t>(t - exif.data());
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t += 10;
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nb_tags--;
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}
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return 0;
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}
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// TODO(jon): tag 1 can be used to represent Adobe RGB 1998 if it has value
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// "R03"
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// TODO(jon): set intrinsic dimensions according to
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// https://discourse.wicg.io/t/proposal-exif-image-resolution-auto-and-from-image/4326/24
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// Parses the Exif data just enough to extract any render-impacting info.
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// If the Exif data is invalid or could not be parsed, then it is treated
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// as a no-op.
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JXL_INLINE void InterpretExif(const std::vector<uint8_t>& exif,
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JxlOrientation* orientation) {
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bool bigendian;
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if (!IsExif(exif, &bigendian)) return;
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size_t o_pos = FindExifTagPosition(exif, kExifOrientationTag);
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if (o_pos) {
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const uint8_t* t = exif.data() + o_pos;
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uint16_t type = (bigendian ? LoadBE16(t) : LoadLE16(t));
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t += 2;
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uint32_t count = (bigendian ? LoadBE32(t) : LoadLE32(t));
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t += 4;
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uint16_t value = (bigendian ? LoadBE16(t) : LoadLE16(t));
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if (type == 3 && count == 1 && value >= 1 && value <= 8) {
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*orientation = static_cast<JxlOrientation>(value);
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}
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}
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}
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} // namespace jxl
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#endif // LIB_JXL_BASE_EXIF_H_
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