I have been saving my digital photos in TIF for the main archive copy
because of the potential for damage to files saved as JPG, which I
have been mostly shooting in. I have started shooting mostly RAW and
making a DNG copy for archiving. I was wondering if as DNG is also a
compressed file, though not as lossy as JPG, it is as susceptible to
damage as JPG. Is it safer to archive in an ucompressed format like
TIF than DNG?
I was thinking of saving the RAW, a DNG copy for future compatability,
a JPG for viewing, and if the DNG can be damaged signicantly by 1 or
more errors, then possibly TIF.
The reason I asked this question is because I read that with JPG files
a single pixel error can ruin the whole photo but is not noticed i a
TIF file. I didn't know DNG files were TIF files. So I should be ok
saving directly to DNG in the camera and making a JPG copy for
viewing.
Thanks
Mike
On Sun, 30 Sep 2007 10:47:29 +0100, John Bean <waterfoot@gmail.com>
wrote:
>Firstly DNG is in fact just another form of TIFF, albeit a
>specialised one designed to contain raw data rather than
>"normal" image data.
>
>Secondly the (optional) compression used in DNG format is
>completely lossless.
>
>Thirdly you don't actually have to compress DNGs at all
>unless you want to.
>
>Don't worry about data security, DNG files are at least as
>safe as any other digital image format.
> The reason I asked this question is because I read that with JPG files
> a single pixel error can ruin the whole photo but is not noticed i a
> TIF file. I didn't know DNG files were TIF files. So I should be ok
> saving directly to DNG in the camera and making a JPG copy for
> viewing.
If you use a compressed TIFF then potentially errors may propagate. The
same could be true of DNG if it uses compression. It depends partly on the
nature of the compression. For instance if each pixel value is stored as a
difference from the last (as with the lossless JPEG* method which uses
predictive encoding) then a single error could ruin the whole image just
like a normal JPEG. As for LZH compression that TIFF often uses, I'm not
quite sure but I suspect an error would propagate too, certainly that seems
to be the case with corrupt zip files.
As regards quality, a 24 bit TIFF will be worse than DNG since some bit
depth will be lost just as it is with JPEG, but 48 bit TIFF will capture
all the information, however it will be bigger than DNG due to redundant
extra bit depth.
A good way to guard against corrupt files (apart from simply backing up of
course) is to make a certain % of PAR2 error recovery files using the
QuickPar program that is often used by downloaders. When archiving images
to a CD or DVD-R, include say 5% PAR2 recovery files and then if the disk
becomes corrupt you can still recover all the files as long as bad blocks
do not exceed that percentage. If I have room left on a DVDR when archiving
a batch of images, I usually fill up the space with some recovery files, it
can't hurt and if could just save your images.
* lossless JPEG should not be confused with normal JPEG, it uses a totally
different compression algorithm which is totally lossless but gives
superior compression to ZIP/LZH type compression.
On Sun, 30 Sep 2007 14:02:06 GMT, MikeM
<mmo45018@bigpond.net.au> wrote:
>The reason I asked this question is because I read that with JPG files
>a single pixel error can ruin the whole photo but is not noticed i a
>TIF file. I didn't know DNG files were TIF files. So I should be ok
>saving directly to DNG in the camera and making a JPG copy for
>viewing.
What camera are you using? Most camera-produced DNGs are
uncompressed so they're fairly immune from harm by
single-bit errors. Personally I've never had a DNG lost by
data corruption - not one - and all my DNGs are compressed
from various raw camera formats using the (free) Adobe DNG
Converter. My current DNG count exceeds 30k.
Pentax K10D. I had the DNG converter set to compress the RAW files.
The DNGs from the camera are bigger than those that are converted, so
I assume they are not comprressed. The photos I lost were all JPGs
that had been backed up to CD-Rs/DVD-Rs.
On Sun, 30 Sep 2007 16:11:59 +0100, John Bean <waterfoot@gmail.com>
wrote:
>On Sun, 30 Sep 2007 14:02:06 GMT, MikeM
><mmo45018@bigpond.net.au> wrote:
>
>>The reason I asked this question is because I read that with JPG files
>>a single pixel error can ruin the whole photo but is not noticed i a
>>TIF file. I didn't know DNG files were TIF files. So I should be ok
>>saving directly to DNG in the camera and making a JPG copy for
>>viewing.
>
>What camera are you using? Most camera-produced DNGs are
>uncompressed so they're fairly immune from harm by
>single-bit errors. Personally I've never had a DNG lost by
>data corruption - not one - and all my DNGs are compressed
>from various raw camera formats using the (free) Adobe DNG
>Converter. My current DNG count exceeds 30k.
On Sun, 30 Sep 2007 21:42:51 GMT, MikeM
<mmo45018@bigpond.net.au> wrote:
>Pentax K10D. I had the DNG converter set to compress the RAW files.
>The DNGs from the camera are bigger than those that are converted, so
>I assume they are not comprressed. The photos I lost were all JPGs
>that had been backed up to CD-Rs/DVD-Rs.
That makes sense, K10D DNG files are uncompressed.
FWIW I don't back up to optical disks, it's got to be the
most unreliable way to store data since the floppy disk, not
to mention the inconvenience. USB 2.0 hard disks are much
more reliable, infinitely faster, and really quite
inexpensive. Very simple to backup as well. Just a thought.
If you really must use optical disks make sure you do a full
verify on every session - never "trust" that a CD/DVD is
written correctly just because the software tells yo there
were no errors.
Been there, done that, still got the burn marks on the
fingers. Never again :-(
John Bean <waterfoot@gmail.com> wrote:
> On Sun, 30 Sep 2007 14:02:06 GMT, MikeM
> <mmo45018@bigpond.net.au> wrote:
>
>>The reason I asked this question is because I read that with JPG files
>>a single pixel error can ruin the whole photo but is not noticed i a
>>TIF file. I didn't know DNG files were TIF files. So I should be ok
>>saving directly to DNG in the camera and making a JPG copy for
>>viewing.
>
> What camera are you using? Most camera-produced DNGs are
> uncompressed so they're fairly immune from harm by
> single-bit errors. Personally I've never had a DNG lost by
> data corruption - not one - and all my DNGs are compressed
> from various raw camera formats using the (free) Adobe DNG
> Converter. My current DNG count exceeds 30k.
>
That is the entire point of making backups; to avoid data corruption. I keep
copies on a hard drive and on DVD [where possible]. Usually, a given veture
will result in enough pictures to fill one or two DVDs. I make a two copies
and move one to a different location from the other. I also keep copies on a
hard drive for easy access. I am not a high volume shooter, but if I was, I
would just buy several hard drives and put them in those external [USB or
SATA] cases and store my images on several hard drives and skip the DVD
archiving altogether. BTW ... this is the method professionals uses
[specifically, I am aware that John Shaw archives exclusively on multiple hard
drives].
--
Thomas T. Veldhouse
You will be advanced socially, without any special effort on your part.
Early last year I backed up the result of a 2-month overseas trip. I
started with DVD-RWs, but as I kept reading everywhere, and being told
by sales people I should be using DVD-Rs, I switched to them. About 8
months later I needed to retrieve some shots from the backup disks but
found there some filest were corrupt. A disk-checking program reported
that all the DVD-Rs had bad patches but none of the DVD-RWs had any.
I checked the disks going back a few years, CD/ DVD-Rs and CD/DVD-RWs
back a few years when I was backing up scans of slides. All the CD-Rs
and DVD-Rs had bad patches but only 1 of the CD-RWs that was a few
years old had a bad patch. The only disks that had no bad patches were
TDK CD & DVD-RWs.
As soon as I could I started backing up to USB drives. So far there
have been no problems, and I won't have to extend my house to store
the backup DVDs.
Mike
On Mon, 01 Oct 2007 00:02:41 +0100, John Bean <waterfoot@gmail.com>
wrote:
>On Sun, 30 Sep 2007 21:42:51 GMT, MikeM
><mmo45018@bigpond.net.au> wrote:
>
>>Pentax K10D. I had the DNG converter set to compress the RAW files.
>>The DNGs from the camera are bigger than those that are converted, so
>>I assume they are not comprressed. The photos I lost were all JPGs
>>that had been backed up to CD-Rs/DVD-Rs.
>
>That makes sense, K10D DNG files are uncompressed.
>
>FWIW I don't back up to optical disks, it's got to be the
>most unreliable way to store data since the floppy disk, not
>to mention the inconvenience. USB 2.0 hard disks are much
>more reliable, infinitely faster, and really quite
>inexpensive. Very simple to backup as well. Just a thought.
>
>If you really must use optical disks make sure you do a full
>verify on every session - never "trust" that a CD/DVD is
>written correctly just because the software tells yo there
>were no errors.
>
>Been there, done that, still got the burn marks on the
>fingers. Never again :-(
On Mon, 01 Oct 2007 22:48:20 GMT, MikeM
<mmo45018@bigpond.net.au> wrote:
>I checked the disks going back a few years, CD/ DVD-Rs and CD/DVD-RWs
>back a few years when I was backing up scans of slides. All the CD-Rs
>and DVD-Rs had bad patches but only 1 of the CD-RWs that was a few
>years old had a bad patch. The only disks that had no bad patches were
>TDK CD & DVD-RWs.
Yes, I've had bad experiences with pretty much all DVDs but
even worse issues with RW types, so I suspect you got a bit
lucky with yours. I still use DVD-RAM (not as backup of
course!) and find it infinitely more reliable than other
rewriteable able DVDs and I treat them much like giant
floppy disks.
>As soon as I could I started backing up to USB drives. So far there
>have been no problems, and I won't have to extend my house to store
>the backup DVDs.
DNGF vs TIF 
Linear Mode
