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Cexif

, 15 Mar 2003
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A small class to read EXIF data from JPEG images.

Sample Image - cexif.png

Introduction

Cexif is a small class to read the EXIF data stored in JPEG images, normally generated by digital cameras.

The code is based on Jhead, written by Matthias Wandel. Jhead offers a lot of switches to parse an image with EXIF tags, but it's plain C. I simply rearranged the functions and the global variables into a simple class.

Another useful article on this topic is here [^], with a bit of details on the EXIF structure. The official document for the "Digital Still Camera Image File Format Standard (Exchangeable image file format for Digital Still Cameras: Exif) Version 2.1" can be downloaded from http://www.bbs-informatique.fr/pdf/photo/Exif_2-1.pdf [^].

You can find some EXIF images at http://www.exif.org/samples.html

Using the code

You can use this class in 2 ways. The simplest is:

Cexif exif;
exif.DecodeExif(hFile);

where hFile is a valid file handle. If the file contains EXIF data, exif.m_exifinfo->IsExif is true, and you can read the fields in exif.m_exifinfo to create a report. The second way is:

EXIFINFO m_exifinfo;
memset(&m_exifinfo,0,sizeof(EXIFINFO));
Cexif exif(&m_exifinfo);
exif.DecodeExif(hFile);

In this case the result is stored in the variable m_exifinfo, and you can delete the exif object without losing the EXIF data.

More EXIF tags

typedef struct tag_ExifInfo {
    char  Version      [5];
    char  CameraMake   [32];
    char  CameraModel  [40];
    char  DateTime     [20];
    int   Height, Width;
    int   Orientation;
    int   IsColor;
    int   Process;
    int   FlashUsed;
    float FocalLength;
    float ExposureTime;
    float ApertureFNumber;
    float Distance;
    float CCDWidth;
    float ExposureBias;
    int   Whitebalance;
    int   MeteringMode;
    int   ExposureProgram;
    int   ISOequivalent;
    int   CompressionLevel;
    float FocalplaneXRes;
    float FocalplaneYRes;
    float FocalplaneUnits;
    float Xresolution;
    float Yresolution;
    float ResolutionUnit;
    float Brightness;
    char  Comments[MAX_COMMENT];
    unsigned char * ThumbnailPointer;
    unsigned ThumbnailSize;
    bool  IsExif;
} EXIFINFO;

If needed, the EXIFINFO structure can be extended to read more tags.

  1. Declare a new field in the EXIFINFO structure (example: float ExposureTime;)
  2. Define a new tag in exif.cpp (example: #define TAG_EXPOSURETIME 0x829A).
  3. Add a new case in the ProcessExifDir function.

Example:

case TAG_EXPOSURETIME:
m_exifinfo->ExposureTime = (float)ConvertAnyFormat(ValuePtr, Format);
break;

ConvertAnyFormat converts automatically the value stored in the tag.

To Do

  • Cexif::EncodeExif : to append the EXIF data into a standard JPEG image.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

No Biography provided

Comments and Discussions

 
QuestionAbout License [modified] PinmemberDejavuh14-May-14 17:17 
AnswerRe: About License PinpremiumDavide Pizzolato15-May-14 6:08 
GeneralRe: About License PinmemberDejavuh15-May-14 13:21 
QuestionWrite exif PinmemberMichael Riosa Nielsen13-Sep-12 6:35 
GeneralError fix Pinmemberyury_i21-Jan-10 4:49 
GeneralRe: Error fix PinmemberDamir Valiulin7-May-10 20:16 
GeneralMy vote of 1 Pinmemberarkilisx19-Oct-09 4:48 
GeneralMaking the demo work on Visual Studio 2008 under Vista PinmemberCodeGibbon30-Nov-08 11:28 
GeneralRe: Making the demo work on Visual Studio 2008 under Vista PinmemberJIAOZONGLU18-Oct-11 23:11 
GeneralDemo program doesn't read EXIF data from Pentax K100D PinmemberNico Cuppen14-Oct-08 5:33 
GeneralRe: Demo program doesn't read EXIF data from Pentax K100D PinmemberDavide Pizzolato14-Oct-08 12:46 
GeneralEXIF GPS tags Pinmemberandycarr19-Jan-08 0:32 
Generalcomments in JPEG files PinmemberMartin081531-May-07 2:26 
GeneralIMC INFO PinmemberAndE0026-Feb-05 4:42 
GeneralOrientation PinmemberTeaShirt26-Aug-04 15:43 
GeneralRe: Orientation Text Descriptions Pinmemberjmeaux14-Aug-05 8:23 
QuestionHow to make a non-Exif jpg an Exif jpg? Pinmembercjjj11-Nov-03 21:22 
AnswerRe: How to make a non-Exif jpg an Exif jpg? Pinmembercjjj20-Nov-03 0:29 
AnswerRe: How to make a non-Exif jpg an Exif jpg? PinmemberJIAOZONGLU18-Oct-11 23:14 
GeneralCan't Read Fujifilm EXIF PinmemberRichard Collins21-Oct-03 3:41 
GeneralRe: Can't Read Fujifilm EXIF PinmemberDavide Pizzolato25-Oct-03 6:03 
GeneralCexif::EncodeExif PinmemberDavid Horner18-Aug-03 18:37 
GeneralRe: Cexif::EncodeExif PinmemberDavide Pizzolato18-Aug-03 21:08 
GeneralExport Exif data PinmemberBengCésar9-Jul-03 2:01 
GeneralRe: Export Exif data PinmemberDavide Pizzolato14-Jul-03 7:58 

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