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Data Loss? Sync'd file is smaller (though GPS info is added) #113

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1.Use as directed
2.Compare file size to original
3.The output from GPicSync file size is smaller.
4.See attached JPG for file size comparison.

What is the expected output? What do you see instead?
I would expect the injected GPS data to make the file larger.  This makes me 
think that the progam is deleting something from my original file.  I have 
compared extended EXIF information and I don't see any loss of EXIF tags or 
data, but GPS data is added as expected.  Where is the file size reduction 
coming from?  What data is being left out?

What version of the product are you using? On what operating system?
Version 1.28 on Win7 and WinXP

Please provide any additional information below.

Original issue reported on code.google.com by jrmcalli...@gmail.com on 6 Apr 2012 at 5:06

Attachments:

GoogleCodeExporter commented 9 years ago 
GPicSync uses Exiftool in the backend to write metadata in the picture file. 
Looking at Exiftool FAQ there's an answer about this:
http://www.sno.phy.queensu.ca/~phil/exiftool/faq.html#Q13

"""
"Why is my file smaller after I use ExifTool to write information?"

There are various specific reasons why this can happen, but the general answer 
is: When ExifTool writes an image, the meta information may be restructured in 
such a way that it takes less space than in the original file.
For instance, the EXIF/TIFF standard allows for blocks of unreferenced data to 
exist in an image. Some digital cameras write JPEG or TIFF-based RAW files 
which contain large blocks of unused data, usually filled with binary zeros. 
The reason for this could be to simplify camera algorithms by allowing 
variable-sized information to be written at fixed offsets in the output image. 
When ExifTool rewrites an image it does not copy these unused blocks. This can 
result in a significant reduction in file size for some images.[...]
"""

You are correct about the file size shrink. It's nothing GPicSync can do about 
and it's not really considered as an issue (the image itself is not touch).

Original comment by francois...@gmail.com on 6 Apr 2012 at 7:09

GoogleCodeExporter commented 9 years ago

Original comment by francois...@gmail.com on 6 Apr 2012 at 7:15