I wanted to build an awesome place for people to discuss module specific issues, but I don't have any more time for this, and there are much better places to discuss Perl-related issues. I'd recommend asking your question on Stack Overflow or on Perl Monks.
If you are looking for a Perl tutorial or Perl-related news, I hope these links will serve you well.
Image-ExifTool
Posted on 2009-03-04 14:23:56-08 by igor77
the order of tags in CR2 file
Hi, Phil!
While working with Exiftool I find that the order of tags in CR2 file may change. I look on some "offset" tags, such as "Preview Image Start", "Thumbnail Offset", "Strip Offsets". For instance when I change thumbnail image or/and preview image - they may change their places. Before changing the order was: thumbnail, preview, raw data; after change: thumbnail, raw, preview. Of course I change the lenght of this tags and the next tag starts accordingly with shift. But why they change their sequence?
Sometimes between raw and preview images there is any information (some kilobytes between preview ends and raw starts), and after change this information moves somewhere (the gap between end and start becomes zero).
In all cases after change CR2 files works well - I don't find any troubles.
The question is: is the order of tags important, or such changes are not critical?
Thanks.
Igor
Direct Responses: 10114 | Write a response
Posted on 2009-03-04 16:05:25-08 by exiftool in response to 10112
Re: the order of tags in CR2 file
Hi Igor,

Changes like this are not important. The only important thing is that the proper offset is stored so software can find the correct data. In a TIFF format file (like CR2) any value longer than 4 bytes has an associated offset, but most offsets are not extracted separately since the offset/size information is contained within a single tag. However, for things like the thumbnailImage, the offset and size are stored in different tags, and exiftool extracts the associated data using a Composite tag. This exposes the offset to you, but it is not significant. See the TIFF specification if you want to learn more about the structure of a TIFF file.

- Phil
Direct Responses: 10115 | Write a response
Posted on 2009-03-04 16:15:50-08 by exiftool in response to 10114
Re: the order of tags in CR2 file
Also, you can try using the -htmlDump feature if you want to get a better feel for this and see how the file is organized.

- Phil
Direct Responses: 10117 | Write a response
Posted on 2009-03-05 06:01:06-08 by igor77 in response to 10115
Re: the order of tags in CR2 file
Hi, Phil,

Thank you very much for irrefragable answer!
The main thing for me today is that nothing crashes after these changes :-)
I have looked the result of the -htmlDump feature. It's impressive! I'm not programmer and I'm not familiar with such things, but it really helps to get better feel for this subject.

Igor
Direct Responses: Write a response