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Table of Contents
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 AiAFManual 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, among others, 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 |
i-Contrast
i-Contrast is a post-processing filter applied by the S120 after the shoot. It can be applied at shoot time (supposedly on the RAW image) using two different pre-sets (see below), or it can be applied on the JPEG image in play mode using four modes.
Applying i-Contrast in play mode is rather pointless, just use your preferred photo editing software to get better control on the exposure. Using i-Contrast at shot time can perhaps get better results if it actually operate on the RAW image: adjusting the exposure before JPEG compression can lead to better results than post-processing on the JPEG image. But actually we don't know how i-Contrast operates at shot time, so - if you have any concerns about a bad exposition - just shot in RAW mode and do post-processing in your preferred software.
One user in this forum post says: I've heard i-Contrast can be used later on. So, the best is to take photos iContrast off, and applying later if necessary. Then you will have more time to check if it is better. The bottomline is, that the iContrast function is only a post processing, and does nothing at the exposure. Therefore you can get even better result from the RAW with PS.. In fact, if you shoot in RAW (or RAW+JPEG) the i-Contrast settings are unavailable.
Anyway, in P mode you can activate i-Contrast in two modes:
- Dynamic Range Correction: to avoid washed-out highlights
- Shadow Correct: to preserve image in shadows
In playback mode you can instead apply i-Contrast in four variant: Auto, Low, Medium and High. Whatever it means!