/src/libjxl/lib/jxl/base/exif.h
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1 | | // Copyright (c) the JPEG XL Project Authors. All rights reserved. |
2 | | // |
3 | | // Use of this source code is governed by a BSD-style |
4 | | // license that can be found in the LICENSE file. |
5 | | |
6 | | #ifndef LIB_JXL_BASE_EXIF_H_ |
7 | | #define LIB_JXL_BASE_EXIF_H_ |
8 | | |
9 | | // Basic parsing of Exif (just enough for the render-impacting things |
10 | | // like orientation) |
11 | | |
12 | | #include <jxl/codestream_header.h> |
13 | | |
14 | | #include <cstddef> |
15 | | #include <cstdint> |
16 | | #include <vector> |
17 | | |
18 | | #include "lib/jxl/base/byte_order.h" |
19 | | #include "lib/jxl/base/compiler_specific.h" |
20 | | |
21 | | namespace jxl { |
22 | | |
23 | | constexpr uint16_t kExifOrientationTag = 274; |
24 | | |
25 | | // Checks if a blob looks like Exif, and if so, sets bigendian |
26 | | // according to the tiff endianness |
27 | 0 | JXL_INLINE bool IsExif(const std::vector<uint8_t>& exif, bool* bigendian) { |
28 | 0 | if (exif.size() < 12) return false; // not enough bytes for a valid exif blob |
29 | 0 | const uint8_t* t = exif.data(); |
30 | 0 | if (LoadLE32(t) == 0x2A004D4D) { |
31 | 0 | *bigendian = true; |
32 | 0 | return true; |
33 | 0 | } else if (LoadLE32(t) == 0x002A4949) { |
34 | 0 | *bigendian = false; |
35 | 0 | return true; |
36 | 0 | } |
37 | 0 | return false; // not a valid tiff header |
38 | 0 | } |
39 | | |
40 | | // Finds the position of an Exif tag, or 0 if it is not found |
41 | | JXL_INLINE size_t FindExifTagPosition(const std::vector<uint8_t>& exif, |
42 | 0 | uint16_t tagname) { |
43 | 0 | bool bigendian; |
44 | 0 | if (!IsExif(exif, &bigendian)) return 0; |
45 | 0 | const uint8_t* t = exif.data() + 4; |
46 | 0 | uint64_t offset = (bigendian ? LoadBE32(t) : LoadLE32(t)); |
47 | 0 | if (exif.size() < 12 + offset + 2 || offset < 8) return 0; |
48 | 0 | t += offset - 4; |
49 | 0 | if (offset + 2 >= exif.size()) return 0; |
50 | 0 | uint16_t nb_tags = (bigendian ? LoadBE16(t) : LoadLE16(t)); |
51 | 0 | t += 2; |
52 | 0 | while (nb_tags > 0) { |
53 | 0 | if (t + 12 >= exif.data() + exif.size()) return 0; |
54 | 0 | uint16_t tag = (bigendian ? LoadBE16(t) : LoadLE16(t)); |
55 | 0 | t += 2; |
56 | 0 | if (tag == tagname) return static_cast<size_t>(t - exif.data()); |
57 | 0 | t += 10; |
58 | 0 | nb_tags--; |
59 | 0 | } |
60 | 0 | return 0; |
61 | 0 | } |
62 | | |
63 | | // TODO(jon): tag 1 can be used to represent Adobe RGB 1998 if it has value |
64 | | // "R03" |
65 | | // TODO(jon): set intrinsic dimensions according to |
66 | | // https://discourse.wicg.io/t/proposal-exif-image-resolution-auto-and-from-image/4326/24 |
67 | | // Parses the Exif data just enough to extract any render-impacting info. |
68 | | // If the Exif data is invalid or could not be parsed, then it is treated |
69 | | // as a no-op. |
70 | | JXL_INLINE void InterpretExif(const std::vector<uint8_t>& exif, |
71 | 0 | JxlOrientation* orientation) { |
72 | 0 | bool bigendian; |
73 | 0 | if (!IsExif(exif, &bigendian)) return; |
74 | 0 | size_t o_pos = FindExifTagPosition(exif, kExifOrientationTag); |
75 | 0 | if (o_pos) { |
76 | 0 | const uint8_t* t = exif.data() + o_pos; |
77 | 0 | uint16_t type = (bigendian ? LoadBE16(t) : LoadLE16(t)); |
78 | 0 | t += 2; |
79 | 0 | uint32_t count = (bigendian ? LoadBE32(t) : LoadLE32(t)); |
80 | 0 | t += 4; |
81 | 0 | uint16_t value = (bigendian ? LoadBE16(t) : LoadLE16(t)); |
82 | 0 | if (type == 3 && count == 1 && value >= 1 && value <= 8) { |
83 | 0 | *orientation = static_cast<JxlOrientation>(value); |
84 | 0 | } |
85 | 0 | } |
86 | 0 | } |
87 | | |
88 | | } // namespace jxl |
89 | | |
90 | | #endif // LIB_JXL_BASE_EXIF_H_ |