convert dng files to dng files?

When I use my K10D and take photos in the dng format, their size is about 16 MB. When, on my computer, I upload these photos in the Adobe dng converter and 'convert' them to a new dng file, they are much smaller: 10 - 12 MB. That's nice as it saves space on my internal and external hard disk.
But can I trust this conversion? I have already noticed that after the conversion, the photos in the 'portrait' modus have to be rotated 90 degrees CCW to display them properly. So at least this information was lost.
So my question: can I totally trust the conversion by the Adobe dng convertor? Is it an 100 % lossless compression?

Thanks,

Myrdinn

I'm not sure why you would convert a DNG to a DNG because you can't do anything useful with it until it's a JPEG or, hopefully, a lossless TIFF.

The RAW converter is for making a conversion to a useable format such as TIFF.

Or am I missing your point?

He's just trying to make them smaller.

G

Yes, if you convert the dng files form your camera by the Adobe dng convertor, they are about 40 % smaller. That makes it easier and cheaper to store them. At least if the quality is still the same...

As far as I know, the Adobe DNG converter is a Huffman-based encoding scheme - ie lossless compression.
The K10D PEF format also uses a simpler Huffman encoding scheme - which is why the PEFs are relatively small. I suspect that putting Adobe DNG compatible compression in the DNG files would have taken too much processor time in camera.

So, yes, as far as I can see you can choose to re-DNG and gain some disk space

Also, the DNG converter can also create a larger file that includes the original, unmodified, source RAW file too - for archiving purposes.

Matt

I thought you could work directly with RAW files like DNG and make corrections that were not possible if you have converted them to JPEG or TIFF?
I was under the impression that if you took a photo with an ISO of 200 and then uploaded the DNG file to your computer you could then adjust the ISO to make it like you had taken the photo with an ISO of 400 inside the computer thus compensating for the error at the time of taking the picture?

Yes, you can make adjustments to the RAW file in the RAW Converter, but when you've finished this initial adjustment you save as a JPEG or TIFF ready for further processing in Photoshop.

Although you can compensate for errors in exposure, it's always better to get it right in camera if you can. Bracketing exposures is a fast and simple way of doing this.

Absolutley right about the better to do it right the first time. However when you are just begining to get to grips with your camera and photography in general, it is a little hit and miss. Those one chance shots are gone in an instant and the more chances you have to save them from the recycle bin the better!