Re: [Libexif-devel] Using libexif

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

Dan,

Your answers make me appreciate the cleverness of the camera manufacturers,
whose digital cameras write to nearly every tag location in the Exif header.

Do you suppose that the controllers in those cameras are Linux-based?

Can you point me to a WEB site where I can learn how to tackle my
application (specifically, reading and writing to Exif headers in JPG files)
from the Linux hardware and software direction?

Benny 

-----Original Message-----
From: Dan Fandrich [mailto:da...@co...] 
Sent: Sunday, December 14, 2008 10:51 PM
To: lib...@li...
Subject: Re: [Libexif-devel] Using libexif

On Sun, Dec 14, 2008 at 10:01:53PM -0800, Benny Smith wrote:
> The reason I cannot compile libexif into a library as you instructed is
that
> Rabbit's Dynamic C is not an ANSI C language.  For instance, instead of
> #include, it requires #use.  There are other subtle differences that I
have
> to deal with in order for Dynamic C to accept and compile the libexif
files.
> 
> I have turned to the Rabbit embedded modules and Dynamic C because I
cannot
> find an 8-bit microcontroller with 64KB of onboard RAM to allow storage of
a
> complete Exif header, if necessary.  The Rabbit RCM2300 has 128K of RAM.

Hubert is right--it's hard to imagine an application that processes JPEG
images that will do anything useful in less than a few MB of memory.
The RAM you have left over from the EXIF table isn't enough for holding
a FAT table for reading an image from a memory card, or running gphoto2
(or something similar) to retrieve an image from serial/USB/Ethernet.
I don't know what your application is, but you'll certainly have plenty
of fun cramming it into a Rabbit!

> I asked about the internals of the libexif/exif-data.h because I am trying
> to understand exactly which libexif files (in the list of over 30) that I
> have to convert to Dynamic C in order for the library to compile and work
> properly.

It all depends on what you're trying to accomplish. You can get away with
just compiling exif-loader.c, exif-utils.c and exif-mem.c (there may be
one or two more) if you want the minimal functionality of loading EXIF
data from an image. If you want to look at individual tags, you'll need just
about the whole thing (minus the MakerNote handlers).  The entire library
(minus the verbose strings) compiles down to a 66 KiB shared library
on i386 Linux, which isn't much by Linux standards but is huge for a
Commodore 64 :^)

> Surely I am not the first person to use libexif for an embedded
application
> where memory is limited and where ANSI C may not be fully supported?

The kinds of embedded applications I'm aware of using libexif are embedded
Linux devices with 32 MB of RAM and an ARM processor.

>>> Dan
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