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Canon PowerShot S120

Exif Tags

Using the exiv2 command linee tool (should be packaged into every GNU/Linux distribution), you can view all the Exif metadata contained in each photo, including unknown values:

exiv2 print -p a -u IMG_1858.JPG

There are several proprietary Canon tags stored for each photo, as far I know, there is not a comprensive guide to that tags. An useful resource can be the Metadata reference tables, an index of the names of all tags recognized by Exiv2 library.

Here are some of the more interesting ones. Notice that Exiv2 library v.0.24 is rather incomplete and sometimes misleading in reporting Canon MakerNote tags!

Camera Settings
Exif.CanonCs.AFPoint	Auto-Focus frame setting. Exiv2 library is incomplete or misleading, here it is the true meaning of values: `(0)` ⇒ None (Manual Focus) `(16390)` ⇒ Face AiAF `Manual AF point selection` ⇒ 1-point
Exif.CanonSi.SubjectDistance	Subject distance, as per manual focus or Auto-Focus. The number seems to be the distance in cm, where infinity is reported as 6553.
Exif.Canon.0x0027	This multi-byte tag contains Dynamic Range Correction and Shadow Correct settings. Byte 4 (counting from zero) is a bitwise representation, under investigation. Byte 16 is the Dynamic Range Correction: 0 ⇒ Off 1 ⇒ Auto 200 ⇒ 200% 400 ⇒ 400%
ISO Speed
Exif.CanonCs.ISOSpeed	ISO speed mode. Version 0.24 of Exiv2 library is missing some values, see issue #1217.
Exif.Photo.ISOSpeedRatings	The actual ISO speed used for the shot.
Exif.CanonSi.ISOSpeed	Manual selection of ISO speed? This value is equal or very close to `Exif.Photo.ISOSpeedRatings`, sometimes it has decimals. This value seems to be always 200 when ISO speed is in auto mode.
Aperture
Exif.Photo.FNumber	F-number: the ratio of the lens's focal length to the diameter of the entrance pupil.
Exif.Photo.ApertureValue	The lens aperture in APEX value. Practically it is always the same value as `Exif.Photo.FNumber`.
Exif.CanonSi.TargetAperture	Its value is always close to the `Exif.Photo.FNumber`, sometimes it differs for few decimal points.
Exif.CanonSi.ApertureValue	Sometimes it differs for few decimal points from `Exif.CanonSi.TargetAperture`.
Exposure
Exif.Photo.ExposureTime	The exposure time in seconds or fractions.
Exif.Photo.ShutterSpeedValue	The shutter speed in the APEX units. It differs slightly from `Exif.Photo.ExposureTime`.
Exif.CanonSi.TargetShutterSpeed	Always equal to `Exif.Photo.ShutterSpeedValue`.
Exif.CanonSi.ShutterSpeedValue	It differs sligthly from `Exif.Photo.ExposureTime` and `Exif.CanonSi.TargetShutterSpeed`.
Ligth Value
Exif.CanonSi.MeasuredEV	May be it is the calculated light value for a proper exposure. See here.
Exif.CanonSi.MeasuredEV2	Unused? Seems to be always -6.0