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

[Walter Roberson]

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

[Duncan Carlsmith]

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?

Answer 1

[Duncan Carlsmith]

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.