Re: [Libexif-devel] [PATCH] usercomment modification in exif utils

[matthieu c. <cas...@fr...>]

Lutz Müller wrote:
> On Sat, 2008-06-14 at 19:58 +0200, matthieu castet wrote:
>> I need to change exif usercomment. I update the exif tools to do that.
>> See the attached patch for cvs.
> 
> I checked in a slightly modified version (for exemple: avoid checking
> for e->data 2 times).
Ok, thanks. But now it always resize the user comment tag and my patch 
avoid that by using 0 padding.
> 
>> I don't manage to build cvs
> 
> Have you tried autoreconf -vis?
No, will try.
> 
>> all the exif data are rewritten and are different from
>> the original picture.
>> This shouldn't happen because I only update usercomment without changing
>> the tag size.
> 
> libexif doesn't modify in place. It loads/saves all EXIF data. By
> default, after loading the EXIF data, libexif makes sure that the EXIF
> data follows the specification (EXIF_DATA_OPTION_FOLLOW_SPECIFICATION).
> If the EXIF data you get is different from the EXIF data you supplied
> (with regard to the content), check if the EXIF data supplied follows
> the specification. Have a look at the debug messages using the -d
> command line option.
Using my patch (usercomment tag size not changed),
the difference with -d is [1].
exiv2 also report difference for ExifTag(0x8769) and 
InteroperabilityTag(0xa005).

May be libexif when rewriting the tags remove some padding ?



[1]
--- /tmp/1      2008-06-15 18:32:44.000000000 +0200
+++ /tmp/2      2008-06-15 18:32:40.000000000 +0200
@@ -1,5 +1,5 @@
  ExifLoader: Scanning 1024 byte(s) of data...
-ExifData: Parsing 11262 byte(s) EXIF data...
+ExifData: Parsing 8931 byte(s) EXIF data...

  ExifData: Found EXIF header.
  ExifData: Found EXIF header.
@@ -50,13 +50,13 @@
  ExifData: Loading entry 0xa403 ('WhiteBalance')...
  ExifData: Loading entry 0xa404 ('DigitalZoomRatio')...
  ExifData: Loading entry 0xa406 ('SceneCaptureType')...
-ExifData: IFD 1 at 3158.
+ExifData: IFD 1 at 3136.
  ExifData: Loading 6 entries...
  ExifData: Loading entry 0x103 ('Compression')...
  ExifData: Loading entry 0x11a ('XResolution')...
  ExifData: Loading entry 0x11b ('YResolution')...
  ExifData: Loading entry 0x128 ('ResolutionUnit')...
-EXIF tags in '/tmp/IMG_0872.JPG' ('Intel' byte order):
+EXIF tags in '/tmp/IMG_0872.JPG.modified.jpeg' ('Intel' byte order):
 
--------------------+----------------------------------------------------------
  Tag                 |Value 

 
--------------------+----------------------------------------------------------
@@ -86,8 +86,8 @@
  Metering Mode       |Pattern 

  Flash               |Flash did not fire, compulsory flash mode. 

  Focal Length        |8.3 mm 

-Maker Note          |2138 bytes unknown data 

-User Comment        |Marseille : Cath 

+Maker Note          |2124 bytes unknown data 

+User Comment        |mct 

  FlashPixVersion     |FlashPix Version 1.0 

  Color Space         |sRGB 

  PixelXDimension     |2592