Exiv2

what i don't understand is if the tag LensModel contain the "good information"
it could be used directly without relaying on lenstype which is buggy in many cases

The aim of exiv2 is to correctly report (and modify) the metadata in an image and that's exactly what we do.

The metadata isn't a single data stream, the manufacturer writes makernotes which may duplicate and contract other tags. In this case Canon have chosen to write 6 tags about your lens and we correctly report them all. Very confusingly, Canon have stored both a 39 byte string and a 74 byte string with LensModel. Is one of those strings nul or space padded? I don't know. I've given you a method to allow you to convert "136" into a description of your lens.

I suggest you discuss this with Canon and let me know their response. However, as things stand, I believe Exiv2 is behaving correctly.

i took a look at the source code you mention
i do know much better c as c++

i see that in structure canonCsLensType several lens definitions are listed for the same lenstype id

i don't find any code which will choose one of the definitions from the list of the definitions

is the list of the definition purely informational for the code reader ?

You'll have to read further into the code (I didn't write it). There's a function that gets called for each tag. For LensType, the function is printCsLensType You'll see the comment #1034 which my change to look in the config file.

When printCsLensType, you can read all the Exif metadata (in the const ExifData* metadata). So, you could do something like:

if (Internal::readExiv2Config(section,value.toString(),undefined) == undefined
  && metadata["Exif.CanonCs.LensType"].toString() == "136" 
  && metadata["Exif.Photo.LensModel"].toString().size()
) {
  return os << metadata["Exif.Photo.LensModel"].toString();
}

Caution I've simply typed in this code to explain the concept. The code has to be debugged and tested and I don't have time at the moment to do this for you.

The code is saying "If this lens isn't mentioned in the config file and Exif.CanonCs.LensType == 136 and Exif.Photo.LensModel isn't an empty string, report the value of Exif.Photo.LensModel.

ok thank you for your code, i will try out your code sample

and also add number 747 because i already have some photos taken with "Canon EF 100-400mm f/4.5-5.6L IS II USM" and others with "Tamron SP 150-600mm F5-6.3 Di VC USD G2" !

regarding my question,
is there somewhere in the code a logic which takes decision if several definitions exist in structure canonCsLensType ?
or are the multiple definitions in canonCsLensType purely informational for the source code reader ?

I don't know the answer to your question about several definitions exist in structure canonCsLensType as I didn't write the code. It's a pity that lens recognition was put into Exiv2 as it involves guess work. Niels looked after this code and left the project when we released v0.25. I added the ~/.exiv2 feature to reduce the maintenance headache. Your questions are bringing back my headache. You will have to read the code. I am unpaid volunteer. Words such as "please" or "thank you" are appreciated.

If you want me to support number 747, could you provide a sample file so that I can test my fix. In addition to changing the code, I add test files to our test suite to ensure the fix does not regress. I only extract the metadata into a .exv file which does not include your image.

Hey, I think my pullrequest should fix your problem rene.

https://github.com/Exiv2/exiv2/pull/20

Hello Mike
I am sorry that so are offended but this was not intention. I thank you for the work you are doing for exiv2.

My question was informational because i didn't understood how adding simply lines in the structure canonCsLensType could make it work.

Yet i have seen patch from mfg92 and i saw that also an additional line is needed in structure lensIdFct which makes the whole more comprehensive.

To my question original question :
why doing complicated things with lenstype and not returning lensmodel in all cases ?
what am i missing ?

and also thanks to Matze for its code to make my lens recognized by exiv2.

I think in darktable the patch will be usable in the near timeframe if the patch is accepted.

But for my NAS it will take some time before a fresh exiv2 version is integrated into it...

Thanks very much indeed to both of you for discussing and working on this. It's my intention to review and accept this patch. I'm on vacation at the moment and arrive home on Wednesday. I'll review and submit this by the weekend. When I submit any patch, I like to update the test suite to be sure I get an alert if the patch regresses. I intend to copy the metadata from images attached to #1304 and #1306 and put them in the test suite.

At the moment, Ben and I are working on a major change on 'master' and regrettably the build has been broken while we have both been on vacation. Getting the build fixed is my first priority when I get home.

To my question original question :
why doing complicated things with lenstype and not returning lensmodel in all cases ?
what am i missing ?

I didn't write Exiv2, so I can only discuss the code as I understand from reading and using it. In general, Exiv2 reports the data in the file with the option -pv (print values). The option -pa (== -pt "translated values") does conversion to "human" values. Figuring out the lens type depends on the Manufacturer's MakeNotes (which are different for every manufacturer). Phil Harvey (of ExifTool fame) described it as a "heuristic". I've seen images for which both Exiv2 and ExifTool get the lens wrong.

Exiv2 is open-source. Everybody is welcome to contribute. You are welcome to find a better way. I have worked on Exiv2 for 10 years and I have never rejected any contributor's patch.

It is my intention to make a "dot" release in September. Exiv2 v0.26.1 will include your patch for both #1304 and #1306. Please provide a test image for "747" and that can also be serviced.