EXIF Header Information

A digital photograph contains more than just the red, green, and blue pixel values. Additionally, information about the photograph and camera is stored within the JPEG image. The format of this meta information follows the EXIF standard. On top of the stardardised information, some camera makers make use of proprietary extensions to the EXIF standard, known as maker tags.

For WebHDR to be able to determine the image exposure, it needs to know the ISO speed, exposure times, and aperture settings with which the photographs were taken. Almost all cameras that we have tested can be used with WebHDR, but this is only because we use some smart software named ExifTool (see below) to 'tidy up' the EXIF header before feeding the photographs to hdrgen.

    EXIF tags in 'cameras/fujifilm_dx10.jpg' ('Intel' byte order):
Tag                 |Value                                                     
Manufacturer        |FUJIFILM                                                  
Model               |DX-10                                                     
Orientation         |top - left                                                
x-Resolution        |72/1                                                      
y-Resolution        |72/1                                                      
Resolution Unit     |Inch                                                      
Software            |Digital Camera DX-10 Ver1.00                              
Date and Time       |1999:01:01 00:03:00                                       
YCbCr Positioning   |co-sited                                                  
Copyright           |ANTHONY    (Photographer) - [None] (Editor)               
Compression         |JPEG compression                                          
Orientation         |top - left                                                
x-Resolution        |72/1                                                      
y-Resolution        |72/1                                                      
Resolution Unit     |Inch                                                      
YCbCr Positioning   |co-sited                                                  
FNumber             |f/4.2                                                     
ExposureProgram     |Normal program                                            
ISO Speed Ratings   |150                                                       
Exif Version        |Exif Version 2.1                                          
Date and Time (origi|1999:01:01 00:03:00                                       
Date and Time (digit|1999:01:01 00:03:00                                       
ComponentsConfigurat|Y Cb Cr -                                                 
Compressed Bits per |14/10                                                     
Shutter speed       |68/10 sec. (APEX: 10)                                     
Aperture            |f/4.1                                                     
Brightness          |56/10                                                     
Exposure Bias       |0.0                                                       
MaxApertureValue    |41/10                                                     
Metering Mode       |Pattern                                                   
Flash               |Flash did not fire.                                       
Focal Length        |5.8 mm                                                    
FlashPixVersion     |FlashPix Version 1.0                                      
Color Space         |sRGB                                                      
PixelXDimension     |1024                                                      
PixelYDimension     |768                                                       
Focal Plane x-Resolu|2151/1                                                    
Focal Plane y-Resolu|2151/1                                                    
Focal Plane Resoluti|Centimeter                                                
Sensing Method      |One-chip color area sensor                                
File Source         |DSC                                                       
Scene Type          |                                                          
EXIF data contains a thumbnail (10238 bytes).


Software for editing EXIF information

There is an abundance of software for viewing the EXIF information within an image file. However, there are not quite as many that allow you to edit it as well. I am particularly fond of the following two. They are both command-line utilities, so you can batch-process any number of photographs.

Command-line tool.
Perl module with an included command-line application for reading and writing meta information in image files. It recognises over 1600 different tags. Image::ExifTool is used on the WebHDR site.