Exif：我无法计算图像的方向

Question

我已经编写了一个小型基本解析器来确定一些 jpeg 图像的方向，但我不清楚如何使用 0x112 标签，我没有找到此信息。关于ImageDescription，DateTime Value，我了解到日期时间跳转到对应的示例地址就可以了，参考：标签 3201 这是值 0200 (ascii) 长度 00000014（20 个字符）和从 APP1 000000C2（十进制 194）开始计算的地址。为定位所做的相同推理不起作用：为什么？

谢谢

APP1 Length: 3710
APP1: Exif
byte order: MM
42: |00|2A|
offset: |00|00|00|08|
dir entry: 0 11
0F01|0200|00000006|00000092|
1001|0200|0000000E|00000098|
1201|0300|00000001|00010000|
1A01|0500|00000001|000000A6|
1B01|0500|00000001|000000AE|
2801|0300|00000001|00020000|
3101|0200|0000000B|000000B6|
3201|0200|00000014|000000C2|
1302|0300|00000001|00020000|
6987|0400|00000001|000000D6|
2588|0400|00000001|000003D6|

Answer 1

因为你没有分享你的代码，所以很难说错在哪里。不过，这里有一种解决方法：

# Make a simple 1x1 black starting image with ImageMagick
magick xc:black start.jpg

# Make a copy with orientation=3 in "3.jpg"
exiftool -orientation#=3 start.jpg -o 3.jpg

# Analyse
exiftool -v -v -v 3.jpg

  ExifToolVersion = 12.00
  FileName = 3.jpg
  Directory = .
  FileSize = 260
  FileModifyDate = 1632816155
  FileAccessDate = 1632816155
  FileInodeChangeDate = 1632816155
  FilePermissions = 33188
  FileType = JPEG
  FileTypeExtension = JPG
  MIMEType = image/jpeg
JPEG APP0 (14 bytes):
    0006: 4a 46 49 46 00 01 01 00 00 01 00 01 00 00       [JFIF..........]
  + [BinaryData directory, 9 bytes]
  | JFIFVersion = 1 1
  | - Tag 0x0000 (2 bytes, int8u[2]):
  |     000b: 01 01                                           [..]
  | ResolutionUnit = 0
  | - Tag 0x0002 (1 bytes, int8u[1]):
  |     000d: 00                                              [.]
  | XResolution = 1
  | - Tag 0x0003 (2 bytes, int16u[1]):
  |     000e: 00 01                                           [..]
  | YResolution = 1
  | - Tag 0x0005 (2 bytes, int16u[1]):
  |     0010: 00 01                                           [..]
  | ThumbnailWidth = 0
  | - Tag 0x0007 (1 bytes, int8u[1]):
  |     0012: 00                                              [.]
  | ThumbnailHeight = 0
  | - Tag 0x0008 (1 bytes, int8u[1]):
  |     0013: 00                                              [.]
JPEG APP1 (96 bytes):
    0018: 45 78 69 66 00 00 4d 4d 00 2a 00 00 00 08 00 05 [Exif..MM.*......]
    0028: 01 12 00 03 00 00 00 01 00 03 00 00 01 1a 00 05 [................]
    0038: 00 00 00 01 00 00 00 4a 01 1b 00 05 00 00 00 01 [.......J........]
    0048: 00 00 00 52 01 28 00 03 00 00 00 01 00 01 00 00 [...R.(..........]
    0058: 02 13 00 03 00 00 00 01 00 01 00 00 00 00 00 00 [................]
    0068: 00 00 00 01 00 00 00 01 00 00 00 01 00 00 00 01 [................]
  ExifByteOrder = MM
  + [IFD0 directory with 5 entries]
  | 0)  Orientation = 3
  |     - Tag 0x0112 (2 bytes, int16u[1]):
  |         0030: 00 03                                           [..]
  | 1)  XResolution = 1 (1/1)
  |     - Tag 0x011a (8 bytes, rational64u[1]):
  |         0068: 00 00 00 01 00 00 00 01                         [........]
  | 2)  YResolution = 1 (1/1)
  |     - Tag 0x011b (8 bytes, rational64u[1]):
  |         0070: 00 00 00 01 00 00 00 01                         [........]
  | 3)  ResolutionUnit = 1
  |     - Tag 0x0128 (2 bytes, int16u[1]):
  |         0054: 00 01                                           [..]
  | 4)  YCbCrPositioning = 1
  |     - Tag 0x0213 (2 bytes, int16u[1]):
  |         0060: 00 01                                           [..]
JPEG DQT (65 bytes):
    007c: 00 03 02 02 02 02 02 03 02 02 02 03 03 03 03 04 [................]
    008c: 06 04 04 04 04 04 08 06 06 05 06 09 08 0a 0a 09 [................]
    009c: 08 09 09 0a 0c 0f 0c 0a 0b 0e 0b 09 09 0d 11 0d [................]
    00ac: 0e 0f 10 10 11 10 0a 0c 12 13 12 10 13 0f 10 10 [................]
    00bc: 10                                              [.]
JPEG SOF0 (9 bytes):
    00c1: 08 00 01 00 01 01 01 11 00                      [.........]
  ImageWidth = 1
  ImageHeight = 1
  EncodingProcess = 0
  BitsPerSample = 8
  ColorComponents = 1
JPEG DHT (18 bytes):
    00ce: 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [................]
    00de: 00 09                                           [..]
JPEG DHT (18 bytes):
    00e4: 10 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [................]
    00f4: 00 00                                           [..]
JPEG SOS
JPEG EOI

# Dump
xxd 3.jpg

00000000: ffd8 ffe0 0010 4a46 4946 0001 0100 0001  ......JFIF......
00000010: 0001 0000 ffe1 0062 4578 6966 0000 4d4d  .......bExif..MM
00000020: 002a 0000 0008 0005 0112 0003 0000 0001  .*..............
00000030: 0003 0000 011a 0005 0000 0001 0000 004a  ...............J
00000040: 011b 0005 0000 0001 0000 0052 0128 0003  ...........R.(..
00000050: 0000 0001 0001 0000 0213 0003 0000 0001  ................
00000060: 0001 0000 0000 0000 0000 0001 0000 0001  ................
00000070: 0000 0001 0000 0001 ffdb 0043 0003 0202  ...........C....
00000080: 0202 0203 0202 0203 0303 0304 0604 0404  ................
00000090: 0404 0806 0605 0609 080a 0a09 0809 090a  ................
000000a0: 0c0f 0c0a 0b0e 0b09 090d 110d 0e0f 1010  ................
000000b0: 1110 0a0c 1213 1210 130f 1010 10ff c000  ................
000000c0: 0b08 0001 0001 0101 1100 ffc4 0014 0001  ................
000000d0: 0000 0000 0000 0000 0000 0000 0000 0009  ................
000000e0: ffc4 0014 1001 0000 0000 0000 0000 0000  ................
000000f0: 0000 0000 0000 ffda 0008 0101 0000 3f00  ..............?.
00000100: 2a9f ffd9                                *...

# Make a copy with orientation=5 in "5.jpg"
exiftool -orientation#=5 start.jpg -o 5.jpg

# Analyse
exiftool -v -v -v 5.jpg

  ExifToolVersion = 12.00
  FileName = 5.jpg
  Directory = .
  FileSize = 260
  FileModifyDate = 1632816155
  FileAccessDate = 1632816155
  FileInodeChangeDate = 1632816155
  FilePermissions = 33188
  FileType = JPEG
  FileTypeExtension = JPG
  MIMEType = image/jpeg
JPEG APP0 (14 bytes):
    0006: 4a 46 49 46 00 01 01 00 00 01 00 01 00 00       [JFIF..........]
  + [BinaryData directory, 9 bytes]
  | JFIFVersion = 1 1
  | - Tag 0x0000 (2 bytes, int8u[2]):
  |     000b: 01 01                                           [..]
  | ResolutionUnit = 0
  | - Tag 0x0002 (1 bytes, int8u[1]):
  |     000d: 00                                              [.]
  | XResolution = 1
  | - Tag 0x0003 (2 bytes, int16u[1]):
  |     000e: 00 01                                           [..]
  | YResolution = 1
  | - Tag 0x0005 (2 bytes, int16u[1]):
  |     0010: 00 01                                           [..]
  | ThumbnailWidth = 0
  | - Tag 0x0007 (1 bytes, int8u[1]):
  |     0012: 00                                              [.]
  | ThumbnailHeight = 0
  | - Tag 0x0008 (1 bytes, int8u[1]):
  |     0013: 00                                              [.]
JPEG APP1 (96 bytes):
    0018: 45 78 69 66 00 00 4d 4d 00 2a 00 00 00 08 00 05 [Exif..MM.*......]
    0028: 01 12 00 03 00 00 00 01 00 05 00 00 01 1a 00 05 [................]
    0038: 00 00 00 01 00 00 00 4a 01 1b 00 05 00 00 00 01 [.......J........]
    0048: 00 00 00 52 01 28 00 03 00 00 00 01 00 01 00 00 [...R.(..........]
    0058: 02 13 00 03 00 00 00 01 00 01 00 00 00 00 00 00 [................]
    0068: 00 00 00 01 00 00 00 01 00 00 00 01 00 00 00 01 [................]
  ExifByteOrder = MM
  + [IFD0 directory with 5 entries]
  | 0)  Orientation = 5
  |     - Tag 0x0112 (2 bytes, int16u[1]):
  |         0030: 00 05                                           [..]
  | 1)  XResolution = 1 (1/1)
  |     - Tag 0x011a (8 bytes, rational64u[1]):
  |         0068: 00 00 00 01 00 00 00 01                         [........]
  | 2)  YResolution = 1 (1/1)
  |     - Tag 0x011b (8 bytes, rational64u[1]):
  |         0070: 00 00 00 01 00 00 00 01                         [........]
  | 3)  ResolutionUnit = 1
  |     - Tag 0x0128 (2 bytes, int16u[1]):
  |         0054: 00 01                                           [..]
  | 4)  YCbCrPositioning = 1
  |     - Tag 0x0213 (2 bytes, int16u[1]):
  |         0060: 00 01                                           [..]
JPEG DQT (65 bytes):
    007c: 00 03 02 02 02 02 02 03 02 02 02 03 03 03 03 04 [................]
    008c: 06 04 04 04 04 04 08 06 06 05 06 09 08 0a 0a 09 [................]
    009c: 08 09 09 0a 0c 0f 0c 0a 0b 0e 0b 09 09 0d 11 0d [................]
    00ac: 0e 0f 10 10 11 10 0a 0c 12 13 12 10 13 0f 10 10 [................]
    00bc: 10                                              [.]
JPEG SOF0 (9 bytes):
    00c1: 08 00 01 00 01 01 01 11 00                      [.........]
  ImageWidth = 1
  ImageHeight = 1
  EncodingProcess = 0
  BitsPerSample = 8
  ColorComponents = 1
JPEG DHT (18 bytes):
    00ce: 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [................]
    00de: 00 09                                           [..]
JPEG DHT (18 bytes):
    00e4: 10 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [................]
    00f4: 00 00                                           [..]
JPEG SOS
JPEG EOI

# Dump
xxd 5.jpg

00000000: ffd8 ffe0 0010 4a46 4946 0001 0100 0001  ......JFIF......
00000010: 0001 0000 ffe1 0062 4578 6966 0000 4d4d  .......bExif..MM
00000020: 002a 0000 0008 0005 0112 0003 0000 0001  .*..............
00000030: 0005 0000 011a 0005 0000 0001 0000 004a  ...............J
00000040: 011b 0005 0000 0001 0000 0052 0128 0003  ...........R.(..
00000050: 0000 0001 0001 0000 0213 0003 0000 0001  ................
00000060: 0001 0000 0000 0000 0000 0001 0000 0001  ................
00000070: 0000 0001 0000 0001 ffdb 0043 0003 0202  ...........C....
00000080: 0202 0203 0202 0203 0303 0304 0604 0404  ................
00000090: 0404 0806 0605 0609 080a 0a09 0809 090a  ................
000000a0: 0c0f 0c0a 0b0e 0b09 090d 110d 0e0f 1010  ................
000000b0: 1110 0a0c 1213 1210 130f 1010 10ff c000  ................
000000c0: 0b08 0001 0001 0101 1100 ffc4 0014 0001  ................
000000d0: 0000 0000 0000 0000 0000 0000 0000 0009  ................
000000e0: ffc4 0014 1001 0000 0000 0000 0000 0000  ................
000000f0: 0000 0000 0000 ffda 0008 0101 0000 3f00  ..............?.
00000100: 2a9f ffd9                                *...

两者的区别：

Exif：我无法计算图像的方向

Exif: I can't calculate the orientation of the images

exif