我正在尝试在 Windows 中使用 从 CR2 图像中提取 JPEG 缩略图exiftool。
我成功地做到了这一点这程序 QuickJPGFromCR2。从描述来看，它似乎从 EXIF 数据中提取 JPEG 预览。生成的文件与原始图像的宽度和高度相同，对于我处理的文件，大小在 1~2 MB 之间。
首先，的输出exiftool .\Kendall_FACS_0002_0100A.cr2如下：
ExifTool Version Number : 10.45
File Name : Kendall_FACS_0002_0100A.cr2
Directory : .
File Size : 25 MB
File Modification Date/Time : 2016:10:20 14:47:47-05:00
File Access Date/Time : 2016:11:21 18:26:10-06:00
File Creation Date/Time : 2017:01:23 14:14:05-06:00
File Permissions : rw-rw-rw-
File Type : CR2
File Type Extension : cr2
MIME Type : image/x-canon-cr2
Exif Byte Order : Little-endian (Intel, II)
Image Width : 5184
Image Height : 3456
Bits Per Sample : 8 8 8
Compression : JPEG (old-style)
Make : Canon
Camera Model Name : Canon EOS REBEL T3i
Preview Image Start : 68120
Orientation : Horizontal (normal)
Preview Image Length : 1708300
X Resolution : 72
Y Resolution : 72
Resolution Unit : inches
Modify Date : 2016:10:20 14:46:19
Artist :
Rating : 0
Copyright :
Exposure Time : 1/100
F Number : 16.0
Exposure Program : Manual
ISO : 100
Sensitivity Type : Recommended Exposure Index
Recommended Exposure Index : 100
Exif Version : 0230
Date/Time Original : 2016:10:20 14:46:19
Create Date : 2016:10:20 14:46:19
Components Configuration : Y, Cb, Cr, -
Shutter Speed Value : 1/99
Aperture Value : 16.0
Flash : Off, Did not fire
Focal Length : 40.0 mm
Macro Mode : Normal
Self Timer : Off
Quality : RAW
Canon Flash Mode : Off
Continuous Drive : Single
Focus Mode : Manual Focus (3)
Record Mode : CR2
Canon Image Size : n/a
Easy Mode : Manual
Digital Zoom : None
Contrast : Normal
Saturation : Normal
Metering Mode : Evaluative
Focus Range : Not Known
Canon Exposure Mode : Manual
Lens Type : Canon EF 40mm f/2.8 STM
Max Focal Length : 40 mm
Min Focal Length : 40 mm
Focal Units : 1/mm
Max Aperture : 2.8
Min Aperture : 23
Flash Activity : 0
Flash Bits : (none)
Zoom Source Width : 0
Zoom Target Width : 0
Manual Flash Output : n/a
Color Tone : Normal
SRAW Quality : n/a
Auto ISO : 100
Base ISO : 100
Measured EV : 6.00
Target Aperture : 16
Target Exposure Time : 1/102
Exposure Compensation : 0
White Balance : Daylight
Slow Shutter : None
Shot Number In Continuous Burst : 0
Optical Zoom Code : n/a
Camera Temperature : 30 C
Flash Guide Number : 0
Flash Exposure Compensation : 0
Auto Exposure Bracketing : Off
AEB Bracket Value : 0
Control Mode : Camera Local Control
Measured EV 2 : 6.625
Bulb Duration : 0
Camera Type : EOS High-end
ND Filter : n/a
Canon Image Type : Canon EOS REBEL T3i
Canon Firmware Version : Firmware Version 1.0.2
Flash Metering Mode : Off
Camera Orientation : Horizontal (normal)
Firmware Version : 1.0.2
File Index : 2
Directory Index : 100
Contrast Standard : 0
Sharpness Standard : 3
Saturation Standard : 0
Color Tone Standard : 0
Contrast Portrait : 0
Sharpness Portrait : 2
Saturation Portrait : 0
Color Tone Portrait : 0
Contrast Landscape : 0
Sharpness Landscape : 4
Saturation Landscape : 0
Color Tone Landscape : 0
Contrast Neutral : 0
Sharpness Neutral : 0
Saturation Neutral : 0
Color Tone Neutral : 0
Contrast Faithful : 0
Sharpness Faithful : 0
Saturation Faithful : 0
Color Tone Faithful : 0
Contrast Monochrome : 0
Sharpness Monochrome : 3
Filter Effect Monochrome : None
Toning Effect Monochrome : None
Contrast Auto : 0
Sharpness Auto : 3
Saturation Auto : 0
Color Tone Auto : 0
Filter Effect Auto : n/a
Toning Effect Auto : n/a
Contrast User Def 1 : 0
Sharpness User Def 1 : 3
Saturation User Def 1 : 0
Color Tone User Def 1 : 0
Filter Effect User Def 1 : None
Toning Effect User Def 1 : None
Contrast User Def 2 : 0
Sharpness User Def 2 : 3
Saturation User Def 2 : 0
Color Tone User Def 2 : 0
Filter Effect User Def 2 : None
Toning Effect User Def 2 : None
Contrast User Def 3 : 0
Sharpness User Def 3 : 3
Saturation User Def 3 : 0
Color Tone User Def 3 : 0
Filter Effect User Def 3 : None
Toning Effect User Def 3 : None
User Def 1 Picture Style : Auto
User Def 2 Picture Style : Auto
User Def 3 Picture Style : Auto
Canon Model ID : EOS Rebel T3i / 600D / Kiss X5
Thumbnail Image Valid Area : 0 159 7 112
AF Area Mode : Off (Manual Focus)
Num AF Points : 9
Valid AF Points : 9
Canon Image Width : 5184
Canon Image Height : 3456
AF Image Width : 5184
AF Image Height : 3456
AF Area Widths : 139 139 139 196 238 196 139 139 139
AF Area Heights : 186 186 186 127 231 127 186 186 186
AF Area X Positions : -1477 -886 -886 0 0 0 886 886 1477
AF Area Y Positions : 0 418 -418 787 0 -787 418 -418 0
AF Points In Focus : (none)
AF Points Selected : 0,1,2,3,4,5,6,7,8
Original Decision Data Offset : 0
Bracket Mode : Off
Bracket Value : 0
Bracket Shot Number : 0
Raw Jpg Size : Large
Long Exposure Noise Reduction 2 : Off
WB Bracket Mode : Off
WB Bracket Value AB : 0
WB Bracket Value GM : 0
Live View Shooting : Off
Focus Distance Upper : 2.16 m
Focus Distance Lower : 1.46 m
Flash Exposure Lock : Off
Internal Serial Number : ZC1954285
Dust Removal Data : (Binary data 1024 bytes, use -b option to extract)
Crop Left Margin : 0
Crop Right Margin : 0
Crop Top Margin : 0
Crop Bottom Margin : 0
Exposure Level Increments : 1/3 Stop
ISO Expansion : Off
Flash Sync Speed Av : Auto
Long Exposure Noise Reduction : Off
High ISO Noise Reduction : Standard
Highlight Tone Priority : Disable
AF Assist Beam : Does not emit
Mirror Lockup : Enable
Shutter-AE Lock : AF/AE lock
Set Button When Shooting : Normal (disabled)
LCD Display At Power On : Display
Add Original Decision Data : Off
Aspect Ratio : 3:2
Cropped Image Width : 5184
Cropped Image Height : 3456
Cropped Image Left : 0
Cropped Image Top : 0
Tone Curve : Standard
Sharpness : 3
Sharpness Frequency : n/a
Sensor Red Level : 0
Sensor Blue Level : 0
White Balance Red : 0
White Balance Blue : 0
Color Temperature : 5200
Picture Style : Auto
Digital Gain : 0
WB Shift AB : 0
WB Shift GM : 0
Measured RGGB : 431 1024 1024 768
VRD Offset : 0
Sensor Width : 5344
Sensor Height : 3516
Sensor Left Border : 152
Sensor Top Border : 56
Sensor Right Border : 5335
Sensor Bottom Border : 3511
Black Mask Left Border : 0
Black Mask Top Border : 0
Black Mask Right Border : 0
Black Mask Bottom Border : 0
Color Data Version : 10 (600D/1200D)
WB RGGB Levels As Shot : 2123 1024 1024 1556
Color Temp As Shot : 5200
WB RGGB Levels Auto : 2028 1024 1024 1606
Color Temp Auto : 4908
WB RGGB Levels Measured : 2028 1024 1024 1606
Color Temp Measured : 4908
WB RGGB Levels Daylight : 2123 1024 1024 1556
Color Temp Daylight : 5200
WB RGGB Levels Shade : 2439 1024 1024 1321
Color Temp Shade : 7000
WB RGGB Levels Cloudy : 2280 1024 1024 1431
Color Temp Cloudy : 6000
WB RGGB Levels Tungsten : 1540 1024 1024 2341
Color Temp Tungsten : 3200
WB RGGB Levels Fluorescent : 1869 1024 1024 2226
Color Temp Fluorescent : 3729
WB RGGB Levels Kelvin : 2123 1024 1024 1556
Color Temp Kelvin : 5200
WB RGGB Levels Flash : 2367 1024 1024 1411
Color Temp Flash : 6303
Average Black Level : 2048 2048 2048 2048
Raw Measured RGGB : 99047 229396 224807 170653
Per Channel Black Level : 2047 2047 2048 2048
Normal White Level : 11767
Specular White Level : 12279
Linearity Upper Margin : 10000
Picture Style User Def : Auto; Auto; Auto
Picture Style PC : None; None; None
Custom Picture Style File Name :
Vignetting Corr Version : 0
Peripheral Lighting : Off
Chromatic Aberration Corr : Off
Peripheral Lighting Value : 0
Original Image Width : 5184
Original Image Height : 3456
Peripheral Lighting Setting : Off
Peripheral Illumination Corr : Off
Auto Lighting Optimizer : Off
User Comment :
Sub Sec Time : 46
Sub Sec Time Original : 46
Sub Sec Time Digitized : 46
Flashpix Version : 0100
Color Space : sRGB
Exif Image Width : 5184
Exif Image Height : 3456
Interoperability Index : R98 - DCF basic file (sRGB)
Interoperability Version : 0100
Focal Plane X Resolution : 5728.176796
Focal Plane Y Resolution : 5808.403361
Focal Plane Resolution Unit : inches
Custom Rendered : Normal
Exposure Mode : Manual
Scene Capture Type : Standard
Owner Name : CAM1100A1
Serial Number : 252076117630
Lens Info : 40mm f/?
Lens Model : EF40mm f/2.8 STM
Lens Serial Number : 00002bc0be
Thumbnail Offset : 55048
Thumbnail Length : 13072
Photometric Interpretation : RGB
Samples Per Pixel : 3
Rows Per Strip : 432
Planar Configuration : Chunky
Strip Offsets : 3513124
Strip Byte Counts : 22248252
Raw Image Segmentation : 2 1728 1888
SRaw Type : 1
Aperture : 16.0
Drive Mode : Single-frame Shooting
File Number : 100-0002
Image Size : 5184x3456
Lens : 40.0 mm
Lens ID : Canon EF 40mm f/2.8 STM
Megapixels : 17.9
Preview Image : (Binary data 1708300 bytes, use -b option to extract)
Scale Factor To 35 mm Equivalent: 1.6
Shooting Mode : Manual
Shutter Speed : 1/100
Create Date : 2016:10:20 14:46:19.46
Date/Time Original : 2016:10:20 14:46:19.46
Modify Date : 2016:10:20 14:46:19.46
Thumbnail Image : (Binary data 13072 bytes, use -b option to extract)
WB RGGB Levels : 2123 1024 1024 1556
Blue Balance : 1.519531
Circle Of Confusion : 0.019 mm
Depth Of Field : 1.38 m (1.35 - 2.73 m)
Field Of View : 31.9 deg
Focal Length : 40.0 mm (35 mm equivalent: 62.9 mm)
Hyperfocal Distance : 5.23 m
Lens : 40.0 mm (35 mm equivalent: 62.9 mm)
Light Value : 14.6
Red Balance : 2.073242
因此，查看二进制数据字段（建议使用该-b选项提取的字段），我们得到：
Dust Removal Data : (Binary data 1024 bytes, use -b option to extract)
Preview Image : (Binary data 1708300 bytes, use -b option to extract)
Thumbnail Image : (Binary data 13072 bytes, use -b option to extract)
标签Preview Image看起来就是我们要找的，而且Thumbnail Image也很有趣（虽然很小）。
运行以下命令：
exiftool -b .\Kendall_FACS_0002_0100A.cr2 > out.jpg
exiftool -b -PreviewImage .\Kendall_FACS_0002_0100A.cr2 > out.jpg
exiftool -b -ThumbnailImage .\Kendall_FACS_0002_0100A.cr2 > out.jpg
前两个命令生成的文件大小为 3.28 MB，而最后一个命令生成的文件大小仅为 25.6KB。所有文件均无法在任何程序中打开。Windows Photo Viewer 提示无法打开该文件，因为the file appears to be damaged, corrputed, or is too large。
使用 ImageMagick 的identify命令将为标签提供以下输出Preview Image：
exiftool -b -PreviewImage .\Kendall_FACS_0002_0100A.cr2 | identify -
identify.exe: no decode delegate for this image format `' @ error/constitute.c/ReadImage/504.
exiftool -b -PreviewImage .\Kendall_FACS_0002_0100A.cr2 | identify jpg:-
identify.exe: Not a JPEG file: starts with 0x3f 0x3f `-' @ error/jpeg.c/JPEGErrorHandler/322.
我注意到互联网上的其他地方也有人使用该-JpegFromRaw选项，但我的 EXIF 数据没有这样的标签。
那么，我到底做错了什么？
答案1
在第一个命令中，您将提取所有原始元数据并将其保存到 out.jpg 中。这会创建一个不是图像的垃圾文件。第二个和第三个命令应该有效，它们对我拥有的 .cr2 样本有效。PreviewImage 是一个嵌入的 jpg，如果您的相机设置为保存 Jpgs+Raw，它应该与创建的 jpg 相同。ThumbnailImage 是一个非常小的 jpg（在我的样本中为 160x120），一些程序可以将其用作缩略图以加快图像浏览速度。
我相信 JpegFromRaw 选项用于从一些较旧的相机中提取预览，它可能不会对您的相机产生任何作用。
您正在使用哪个版本的 exiftool（类型exiftool -ver）？
exiftool -b -PreviewImage .\Kendall_FACS_0002_0100A.cr2 > out.jpg和都exiftool -b -ThumbnailImage .\Kendall_FACS_0002_0100A.cr2 > out.jpg应该可以工作。
编辑： 经过我们进行的一些测试，似乎 PowerShell 假定 exiftool 的输出是 ASCII，并将其转换为 Unicode，从而破坏了输出。
与此相关的网页：
https://brianreiter.org/2010/01/29/powershells-object-pipeline-corrupts-piped-binary-data/
https://blogs.msdn.microsoft.com/sergey_babkins_blog/2016/12/29/un-messing-unicode-in-powershell/
总之，命令本身没有问题，问题在于 Powershell 对原始二进制数据的处理。在 CMD 中运行命令会产生预期的输出。