[NTLUG:Discuss] OT: digital camera question

[steve]

Fred James wrote:

> I then took 3 photos - one at each of the resolutions available on the 
> camera - and:
> (1) Copied them from the camera to XP - all photos good.
> (2) Copied them from XP to Linux - all photos good.
> (3) Copied them from camera to Linux - high and medium bad - only the 
> low resolution was good
> (4) Deleted all the photos on the camera
> (5) Copied the good photos (that had been copied in step 2 from XP to 
> Linux) from Linux to the camera
> (6) Copied them back from the camera to Linux - all photos good.
> 
> But I wondered ... and so I ...
> 
> (7) Copied these copies from the camera to XP, and "no preview 
> available" was the message for all of them
> 
> Then I thought I'd try that again in a slightly different route ... once 
> again I deleted all the pictures on the camera (at the camera) and I 
> took 3 new photos - one at each of the resolutions available on the 
> camera - and:
> (8) On Linux, using GIMP to look directly at the camera as a disk - the 
> high and medium resolution were bad, but the low resolution was good
> (9) Copied the files from the camera to XP - all photos looked good
> (10) Copied the files from the camera to Linux - high and medium bad - 
> low resolution good

Well, it's hard to deduce anything from all of that.

However:

* If you *ever* get back a particular photo as 'good' - then later,
   that same photo as 'bad' (which I think happened at (1) and (3)) -
   then it can't be anything to do with how the camera snapped the photo
   and stored it in its memory - it either did it right, or it didn't -
   and if it screwed it up, it would be wrong for XP and Linux.

* If copying the photo from XP to Linux got you good photos but copying
   that same photo via a different route makes it go bad (as in step (2)
   and (3)) - then it can't be a peculiar 'dialect' of JPEG that GIMP
   doesn't understand because it's the same file, just transferred by two
   different means.  So we can rule that out.

* If you ever had a photo that read back badly on both Linux and Windows
   then we could rule out a problem in data transfer due to a problem in
   Linux - and whilst it *looks* like that happened in step (7), we can't
   be sure about that.  Maybe the camera stores preview photos somewhere
   as well as the main picture - and copying a photo into it's memory
   from Linux would presumably circumvent that mechanism.  So without
   knowing how XP gets the previews, so unfortunately, I guess that's
   not 100% conclusive either way.   Did you transfer the photo's from
   the camera into XP using some kind of special tool - or were you
   just treating it like a disk drive?  (The latter would have been a
   more conclusive test).

So all of this evidence tend to point toward a software glitch as Linux
reads large files off the USB port.  But I'm pretty sceptical about
that.  I have two digital cameras, two thumb drives, my son's MP3 player
and a couple of USB hard drives - and Linux 'just works' with all of
them, so I find it hard to believe there's some kind of data transfer
problem with Linux specifically - unless the blame lies with the camera
itself.

But a lot of storage/transfer problems could be of an intermittant
nature - so it's hard to say whether you havn't seen a 'real' problem
with XP because it works correctly (where Linux doesn't) - or whether
the hardware in the camera is just flakey and we just don't have a
sufficiently large statistical sample to see that.

Copying files back and forth onto a flash-memory device such as the
camera's memory results in the data being put into different places
on the chip each time you do it (in fact, because flash memory 'wears
out' after many thousands of write cycles, the design of flash memory
file systems deliberately causes data to be written to different places
each time in order to avoid hitting the same memory cells time after
time and thereby wearing them out prematurely).

So if you had a bad spot in the camera's memory, the result would be
intermittant file corruption with no obvious pattern to it. 
Furthermore, large files would be statistically more likely to hit
a bad patch than small files - so I guess that kinda fits.

So we're left with flakey/intermittant memory in the camera or some kind
of data transfer problem to Linux - and no real way to tell the
difference.

> As for a memory card - I am using the camera's built in memory, as I 
> wasn't sure I wanted to buy any more memory for this camera just yet.

Yeah - given this problem, I could see that!

> This almost sounds like I am making it up.

No, not at all.