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Re: [Openexr-devel] EXIF meta data attributes in headers

From: Thomas Mansencal
Subject: Re: [Openexr-devel] EXIF meta data attributes in headers
Date: Thu, 18 Jul 2013 10:10:28 +0100
Hi Lars,

CCIng back the mailing list that got lost.

exiftool can extract them using the following parameters:

exiftool -xmp -b _MG7890.dng

However I ran into something very annoying: Basically when I convert a CR2 file into DNG using Adobe DNG Converter, the essential exif data is not propagated to the embeded XMP data which is not the case when using Bridge / Camera Raw with the generated sidecar XMP.

Here are some various XMP data generated by different process:

- Conversion of a CR2 file with Adobe DNG Converter:
https://gist.github.com/KelSolaar/6027430
See how there is nothing related to camera data? Exposure, focal length, etc...

- XMP Sidecar generated by Bridge / Camera Raw:
https://gist.github.com/KelSolaar/6027420
Now we have the relevant exif attributes.

- Dng editing in Bridge / Camera Raw:
https://gist.github.com/KelSolaar/6027452
A lot of development data but no exif relevant data.

So question is: Is there a way to easily propagate / convert the exif data to xmp.

The ideal workflow if Open Exr was to use XMP as I "see" it would be something like that: Given a CR2 / DNG file, a command line tool ( Like exiftool ) could be run to create / update the Open EXR file XMP attribute with the data from the source files BUT this data would need to include the relevant EXIF tags.

Thomas






Thomas Mansencal | thomasmansencal.com
[  thomasmansencal.blogspot.com  |  github.com/KelSolaar  ]


2013/7/18 Lars Borg <address@hidden>
There might be a libtiff tool that can extract or print a selected tag (700 or XMP) from a TIFF file.
Worth trying. Could you look for that?

Lars


From: Thomas Mansencal <address@hidden>
Date: Wednesday, July 17, 2013 9:16 PM
To: Lars <address@hidden>

Subject: Re: [Openexr-devel] EXIF meta data attributes in headers

Hi Lars,

Thanks for the details.

By quick I was thinking like using a Python script or something like that: extracting the data with Python and copying it to the exr with exrstdattr using the -string flag.

Thomas



2013/7/18 Lars Borg <address@hidden>
In TIFF and DNG all XMP data is stored in tag 700 in IFD 0.
Tag 700 is a byte-sequence with a specified length.
The contents of tag 700 should be copied in its entirety, exactly as is, to a string in EXR. 
No transcoding of the XMP packet is needed.

Not sure what you mean by quick.

Pseudocode:
  • get offset to IFD 0
  • search IFD 0 for tag 700
  • get length and offset to XMP packet
  • Make EXR attribute: "XMP", "string", XMP packet
Lars


From: Thomas Mansencal <address@hidden>
Date: Wednesday, July 17, 2013 9:01 AM
To: Piotr Stanczyk <address@hidden>
Cc: Lars <address@hidden>, "address@hidden" <address@hidden>

Subject: Re: [Openexr-devel] EXIF meta data attributes in headers

Piort: That would be fantastic if you can agree on something that lands in the official specs.

Lars: I there a quick way to copy the XMP data from a DNG file which is binary serialised to the string attribute of an EXR file?

Thomas



2013/7/17 Piotr Stanczyk <address@hidden>
Sounds interesting ... will take a closer look.

- Piotr
From: openexr-devel-bounces+pstanczyk=address@hidden [openexr-devel-bounces+pstanczyk=address@hidden] on behalf of Lars Borg [address@hidden]
Sent: 17 July 2013 10:22
To: Thomas Mansencal
Cc: address@hidden

Subject: Re: [Openexr-devel] EXIF meta data attributes in headers

Yes, one XMP attribute of type string.

Lars


From: Thomas Mansencal <address@hidden>
Date: Wednesday, July 17, 2013 7:15 AM
To: Lars <address@hidden>
Cc: "address@hidden" <address@hidden>
Subject: Re: [Openexr-devel] EXIF meta data attributes in headers

To be honest with you either way I don't mind, I have no particular preferences. I just feel that being able to embed exif data is important. We are doing that at work but this is not using any standards since they don't exists. 

Regarding XMP how would you do that, serialize / dump everything in an OpenEXR attribute?

Thomas



2013/7/17 Lars Borg <address@hidden>
Thomas,

Why not use XMP instead?
XMP includes all of EXIF + Dublin Core ++

Lars

From: Thomas Mansencal <address@hidden>
Date: Tuesday, July 16, 2013 11:47 PM
To: "address@hidden" <address@hidden>
Subject: Re: [Openexr-devel] EXIF meta data attributes in headers

Hi,

I'm resurrecting that thread after 7 years, I basically wanted to know if there has been more discussions about that matter in the recent years.

The fact there is no standard attributes for common camera data prevents a bit the format to be used as a solid input container for photo processing applications or anything relying on EXIF data. For instance if you want to stitch EXR files with PTGui you will have to enter your data manually.

I think it would be really important trying to establishing a standard list of attributes as suggested by Thomas Lock, the exrstdattr already provides a list of them, maybe completing / updating this one?

Cheers,

Thomas




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