How do I decode DigitalCamera.MakerNote returned by imfinfo as a vector of doubles?

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Duncan Carlsmith 2023-6-24

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回答： Duncan Carlsmith 2023-6-24

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Walter Roberson 2023-6-24

is it currently uint8? Of so then typecast and maybe swapbytes

Duncan Carlsmith 2023-6-24

The data returned by imfinfo is double but appears to be all positive integers and I've tried char(V) and variants of char((u)intXX(V)). Can you be more explicit about using swapbytes?

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Answer 1

Duncan Carlsmith 2023-6-24

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Answering my own question after much ferreting around. It appears that the APPLE makernotes file is a BLIST, a binary version of a property list (plist), and MATLAB's imagesci.rjpg8cimf, invoked from imfinfo, must just throw up its hands and encode the makerfile as a bunch of integers and return a doubles vector.

The EXIFTools source code in PERL for decoding the BLIST is at

https://github.com/exiftool/exiftool/blob/master/lib/Image/ExifTool/Apple.pm

and references

https://medium.com/@karaiskc/understanding-apples-binary-property-list-format-281e6da00dbd

A python decoder is at

https://docs.python.org/3/library/plistlib.html

Discussion: https://stackoverflow.com/questions/27509319/decoding-data-from-plist-file

It would be great if imfinfo were as complete as EXIFinfo. Not only does imfinfo not decode the MAKERNOTES, but it skips over quite a lot of other information.

It is possible to download and install EXIFinfo for various OSs from

https://exiftool.sourceforge.net/

and presumably to invoke it on a file programmatically from MATLAB but that makes its use out of the range of the novice user that I am writing code for, someone who never goes under the hood.

FYI, I've found a few free EXIFinfo servers including

https://www.metadata2go.com/view-metadata

https://jimpl.com/

and one with API access

https://www.conversion-tool.com/api-access/

but that API requires you put your image on a server someplace so you can't just upload a file via a MATLAB RESTFUL call. Not all of these services produce information identical to EXIFTools but they do return APPLE makernotes iPhone acceleration of gravity vector (from the built-in linear accelerometer chip sensor. This data and the bearing from the 3-axis magnetometer (compass) tell you the orientation of the camera locally and given the GPS info the orientation in celestial coordinates, which is what I'm after.