Value Conversions

"Under the Hood" of ExifTool

This page is a work in progress, and will be used to explain some of the details about how ExifTool works.

Value Conversions

When ExifTool reads or writes the value of a tag, there are 3 separate conversions applied to each value, resulting in 4 different levels for the value of each tag. By default, users interact only with the human-readable ("PrintConv") value, but other levels are exposed through various exiftool options:

  1. The "PrintConv" value is the final human-readable value which has been converted for display. Often, the "PrintConv" conversion will translate numbers into words for better readability. The -lang option is used to specify the language for this conversion.
  1. The "ValueConv" value is a numerical value, suitable for use in calculations. Typically, this value is converted to standard units (ie. degrees, meters, or seconds) to make calculations simpler. This value is returned when the -n option is used.
  1. The "Raw" value is the value after initial formatting is applied to the binary data from the file. Most tags have no separate "ValueConv" conversion, so for these tags the "Raw" value is the same as the "ValueConv" value. This value may be seen by using the -v option.
  1. The "Binary" value is actual binary data stored in the file. This data is displayed in hexadecimal form with the -v3 option, or by using the -htmlDump feature. Note that this value is not related to the -b (-binary) option, which actually returns the "ValueConv" value and is used for tags where this value can not be presented in a simple text format.

Below are some examples of these different values for a few tags:

Tag3. PrintConv2. ValueConv1. Raw0. Binary
OrientationHorizontal (normal)11
00 01
GPSLatitude45 deg 20' 11.00"45.336388888888945 20 11
00 00 00 2d 00 00 00 01
00 00 00 14 00 00 00 01
00 00 00 0b 00 00 00 01
ExposureTime1/300.033333333330.03333333333
00 00 00 01 00 00 00 1e
ShutterSpeedValue1/300.03333333346291764.90689059
00 00 4d 9c 00 00 0f d1

Last revised June 25, 2009

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