Re: [Libexif-devel] Question about JPG file access and ExifHeaderaccess

[Benny S. <ich...@pa...>]

Jan and Dan,

Thanks for your replies.

Since I do NOT need to copy the entire JPG file in order to change the Exif
header, I will not do so.

Once the compact flash card is initialized and a JPG file is opened, I will
use libexif to copy the entire Exif header, add the GPS information, and
then re-write the Exif header back to the JPG file.  Obviously, libexif can
handle all of that.

However, I am still not clear on which libexif functions to utilize.

I am searching the libexif documentation for a tutorial or README file or
something that tells how the overall library actually functions and explains
which library files contain the necessary functions for each operation.  I
have been able to figure some of that out from the names of the functions
and from the occasional comments in the code.  But I still do not understand
exactly what I am doing.

Thanks,

Benny


-----Original Message-----
From: Jan Patera [mailto:pa...@pi...] 
Sent: Friday, January 02, 2009 3:18 AM
To: lib...@li...
Cc: ich...@pa...
Subject: Re: [Libexif-devel] Question about JPG file access and
ExifHeaderaccess

Benny,

> Back to the memory issue (not an issue in high-level applications on a
> PC, etc.), are the libjpeg library functions reading/writing an entire
> JPG file?

yes, libjpeg indeed reads and decompresses entire JPEG into memory.
But to parse (and change) the EXIF data you do not need libjpeg at all!!!

The folder libexif/libexif/libjpeg is now empty. I don't know why but
Lutz (the principal author of libexif) removed 4 files .C/.H from there on
2005.03.30. These files were enough to parse EXIF data. These files were
jpeg-data.c
jpeg-data.h
jpeg-marker.c
jpeg-marker.h

I have been successfuly using these files for years and I didn't notice
their removal from libexif till now.

My suggestion for your is to dig for these file here:

http://libexif.cvs.sourceforge.net/viewvc/libexif/libexif/libjpeg/?hideattic
=0&pathrev=MAIN

 --- Jan



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