Confused about RAW format

[HuntingMartians]

I use to own a pentax ist ds and I chose to take photos in the raw format which for pentax was ".pef" files. Now when I edited this pef file the original remained unaltered but a small file which was a .xmp was created and that held the information for the settings you altered leaving the pef in its original state.

In my new pentax k20d I can choose to save as adobe raw ".dng" as well as ".pef". I chose .dng this weekend. Now I noticed when opening the .dng file and making alterations to it. These alterations were actually saved to the dng file and not another file.

So my question regarding adobe .dng files is...will making repeated alterations to the file degrade it (as it is saving over the file unlike .pef which creates a .xmp file)?

 

[pxl8]

afaik dng is just a raw file with the settings embedded into the same file. Changes you make are to the settings rather than the image data.

 

[Gandhi]

^^yep^^

it's just that photoshop used to create an .xmp sidecar file with the settings in it and .dng embeds the settings into it's file. It reads the raw data from the file then applies the settings contained within.

So you're safe!

 

[Slapo]

Repeated alterations shouldn't degrade a dng, but converting to a dng from a native raw format can cause some loss, although I've only seen it with Sigma raw files.

 

[Anthony.Ralph]

Repeated alterations should degrade a dng,

[..]

I'm not at all sure that is true...

Anthony.

 

[Steep]

The trick then would be to back up your raw files before working on them so that you always have an original to fall back on.

or

Use software that does not save changes to the raw file at all.

 

[HuntingMartians]

Hmmm seems to be a few differing opinions to whether repeated alterations to the .dng file will degrade it or not.

 

[Gandhi]

Seriously.

They wont. the only difference with .dng and a normal RAW file with .xmp is that the .xmp is embedded into the file effectively. The data remains the same, only the interpretation changes. You always have the option to go back to the original, untouched .dng file.

Now, as to whether or not you lose any information if you convert from a proprietary RAW file such as .NEF or .(whatever canon calls it) or .(whatever olympus calls it) etc is an entirely different K of F.

 

[Slapo]

I'm not at all sure that is true...

Anthony.

Sorry, that was supposed to be shouldn't in http://www.talkphotography.co.uk/forums/showpost.php?p=822569&postcount=4.
I've fixed it.