1. Exiv2 vs. ExifTool
    1. Exiv2
      1. Features:
    2. Exiftool
      1. Features:
    3. The Test
      1. exiv2 Pros:
      2. exiv2 Cons:
      3. exiftool Pros:
      4. exiftool Cons:
    4. Conclusion

Exiv2 vs. ExifTool

For our Placeholder Thumbnail Feature, we need to write the extracted metadata from the original image to its thumbnail. Furthermore we need a reliable metadata "backend" that acts as a fallback when our internal pure-python metadata libraries fail (e.g. Camera RAW files). This article evaluates two well-known tools, exiv2 and exiftool for their "picurl suitability".

Exiv2

  • Exiv2 Website
  • developed since 2004
  • written in C, no external dependencies

Features:

Quoting from the exiv2-Website:

  • print the Exif metadata of JPEG, TIFF and several RAW image formats as summary info, interpreted values, or the plain data for each tag
  • print IPTC and XMP metadata
  • print, set and delete the JPEG comment of JPEG images
  • set, add and delete Exif, IPTC and XMP metadata of JPEG images
  • adjust the Exif timestamp (that's how it all started...)
  • rename Exif image files according to the Exif timestamp
  • extract, insert and delete Exif, IPTC and XMP metadata and JPEG comments
  • extract, insert and delete the thumbnail image embedded in the Exif metadata
  • fix the Exif ISO setting of picture taken with Nikon cameras

Exiftool

  • Exiftool Website
  • developed since 2003
  • written in Perl, self contained .exe/.img distributions for Windows/Mac OS (no Perl interpreter needed).

Features:

Quoting from the exiftool-Website:

  • Powerful, fast, flexible and customizable
  • Supports a large number of different file formats
  • Reads EXIF, GPS, IPTC, XMP, JFIF, MakerNotes, GeoTIFF, ICC Profile, Photoshop IRB, FlashPix, AFCP, ID3 and more...
  • Writes EXIF, GPS, IPTC, XMP, JFIF, MakerNotes, ICC Profile, Photoshop IRB, AFCP and more...
  • Reads and writes maker notes of many digital cameras
  • Shifts date/time values to fix timestamps in images
  • Renames files and organizes in directories (by date or by any other meta information)
  • Extracts thumbnail images, preview images, and large JPEG images from RAW files
  • Copies meta information between files (even different-format files)
  • Deletes meta information individually, in groups, or altogether
  • Sets the file modification date from EXIF information
  • Supports alternate languages in XMP and MIE information
  • Processes entire directory trees
  • Creates text output file for each image file
  • Automatically backs up original image when writing
  • Organizes output into groups
  • Conditionally processes files based on value of any meta information
  • Ability to add user-defined tags
  • Recognizes thousands of different tags
  • Tested with images from thousands of different camera models
  • Advanced verbose and HTML-based hex dump outputs

The Test

I tested two key abilities of exiv2 and exiftool: the JPEG thumbnail extraction for a bunch of photos and writing IPTC tags to the generated thumbnails. My testsuite consisted of 157 JPEGs with embeded EXIF Metadata and Thumbnails, each at 6 Megapixel, Total size of the directory: 227 MB.

In the test I invoked the exiv2/exiftool binaries from a python script (subprocess), which also measured the time for the task. For the thumbnail extraction, the globbing options of the tools were used (i.e. exiv2 -et *.jpg vs exiftool -b -ThumbnailImage *.jpg -w _thumb-exiftool.jpg). The IPTC write test was conducted by invoking one exiv2/exiftool instance for each photo (exiv2 -M "add Iptc.Application2.City Wien" PHOTO_001.jpg vs. exiftool -iptc:city=Wien PHOTO_001.jpg).

Here are the amazing results: 

 exiv2 Thumbnail extraction execution took: 0.639 Seconds
 exiv2 IPTC Write test execution took: 2.630 Seconds
 Exiftool Thumbnail extraction execution took: 4.497 Seconds
 Exiftool IPTC Write test extraction execution took: 144.522 Seconds

which means that Exiftool is approx. 54 times slower than exiv2 when it comes to writing metadata and 7 times slower for the thumbnail extraction.

exiv2 Pros:

  • BLAZING FAST , also when writing Metadata Tags to images
  • intuitive tag syntax
  • pyexiv2 binding (still experimental)
  • intuitive output configuration

exiv2 Cons:

  • doesn't work with Photoshop Files
  • inflexible Thumbnail Extraction (can only be extracted to the same directory with a -thumb suffix -> problem on read-only media), pyexiv2 provides a convenience method pyexiv2.Image.dumpThumbnailToFile(path) to set a path.
  • limited support of MakerNotes/RAW formats (but steadily growing)
  • doesn't autobackup image files when writing metadata to them (not necessary for our purpose)
  • no IPTC/EXIF <-> XMP conversion (but planned by the developers)
  • currently unable to write multi-line JPEG Comments, returns only last line of multiline JPEG comments when using Irfanview as tag creator . Need this functionality for our picurl directives.
  • Installation on MacOS X might be a challenge (exiv2 is distributed as Fink Package)

exiftool Pros:

  • extracts metadata from nearly any multimedia file format (not just images)
  • comprehensive support of raw files
  • comprehensive support of metadata standards (EXIF, proprietary Makernotes,...)
  • copy meta information between files
  • tag conversion functions

exiftool Cons:

  • SLOOOOOOOOOW when writing metadata to files
  • no Python binding, can only be invoked via shell
  • problems with piping on win32.

Conclusion

For our task (writing metadata of original images to the extracted thumbnails), exiv2 is definitely better suited than exiftool.