Can I extract Canon SX30 face-detection boxes from image metadata?
Asked 8/9/2011
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On a Canon SX30, images shot with Face Detect AF can show review boxes around detected faces. White boxes indicate the face used for autofocus, while gray boxes indicate other detected faces.
I can find metadata related to the autofocus point, but is there any EXIF or maker-note data that records the positions of the gray face-detection boxes so they can be extracted programmatically?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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EXIF is standards based, so info such as this that would be specific to a particular camera maker or even model would likely not be easily deciphered. Typically this kind of information is in what are known as 'maker notes" which are areas of EXIF reserved for platform specific info. Unfortunately, this info is not exposed by Canon, nor do they tell anyone what or how they use this info.
There are those that have done some work to decipher this info, but often it is camera specific and a 'best guess': Scroll down to Appendix 5 in this document:
http://park2.wakwak.com/~tsuruzoh/Computer/Digicams/exif-e.html
For Canon, I find that the Canon supplied tools often have features that detect focus points etc, such as ZoomBrowser. However, I have not seen any 'face detect' information.
Originally by user4880. Source · Licensed CC BY-SA 4.0
user4880
15y ago
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Probably not in any documented, easily usable way. Standard EXIF generally does not include camera-specific face-detection box locations. Information like this is more likely stored in Canon maker notes, which are proprietary and not publicly documented by Canon.
Some reverse-engineering efforts exist for Canon metadata, but they are often model-specific and only partial or best-guess interpretations. So while the focused face/AF point may be available, the non-focused gray face boxes are unlikely to be reliably extractable unless someone has specifically decoded that data for the SX30.
Canon’s own software may display some camera-recorded focus information, but based on the community answers, face-detect box data for those gray boxes is not known to be exposed there either.
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