I did a conversion of some Leica dng files from the camera through the Adobe DNG converter and noticed that the files went from 10MB to 6MB then I did a similar conversion with some CR2 files from my Canon 5D and noticed that a similar size reduction happened.

Before I get rid of the out of camera RAW files does anyone know if this is normal for Adobe DNG conversions? And if it is why is it not listed in one of the reasons to use DNG?

The settings that I am using in the Adobe DNG conversion software version 4.0 are:
JPEG Preview = Full Size
Compression = Compressed (lossless)
Preserve RAW Image
Do Not Embed Original RAW file.

Is the lossless compression safe?
Does anyone know?

Perfectly safe lossless compression, and perfectly natural reduction in size. I have no idea why you think this has not been promoted or publicized.

Out of all the reasons that I have heard to switch to DNG size was never mentioned. I have heard of having one file instead of 2 (with xmp) but never a size savings in MB/GB.

Is the size difference proving to be a problem for you? I have read comments on numerous forums from people who say that the savings in size is one of the primary reasons they use the DNG format. The reduction in size on my camera is about 50%. I remember reading information back when I first started using DNG that the size difference will vary from camera to camera. As was stated, the compression algorithm used in the DNG format applies lossless compression. If you question the, convert one of your images to DNG and then edit both that file and the original raw image and compare the results. It has been stated by Thomas and others from Adobe that there is no loss of data, and I haven't found that to be the case. But if the size difference bothers you, or you don't trust Adobe, just use the original raw images downloaded from your camera.

The size difference is great. I just am concerned that I might be throwing away data without realizing it. I would hate to find myself missing data that could be useful a few years from now because I decided to convert to DNG to save space.

Well, I guess you can be concerned as much as you want to be. Adobe says there is no data loss. Why don't you convert one of your raw images to the DNG format, put the DNG file in the same folder with the original raw image, open them together in Camera Raw and apply the same changes to both images, and then compare them? I can assure you all are now how to, and you can read from others, but that isn't going to really do much good. I am very comfortable using the DNG format. If you are not, then don't use it.

Aaron,

My CR2 files from Canon 20D are about 8-12% less in compressed DNG format than in CR2 format. The difference is due mostly to the fact, that the CR2 includes an 1526x1024 JPEG version (totally useless), beside a 384x256 preview; together 750KB. The DNG I get with this size includes a 256x171 preview and an 1024x683 JPEG version, together 234KB.

Anyway, the gain in size reduction in this case is not worth of mentioning.

As to the statement that there is no data loss: it is simply not true. The question is not if there is data loss, bu if the loss is relevant. I can't answer this at the moment.

G Sch,

Thanks that is the clearest response that I have heard on this subject.

My Pentax K10D shoots DNG (as well as PEF), The PEF is compressed in the
camera the DNG is not. However, I still shoot DNG and then I run them
through Adobe DNG Converter to add the compression. My 16MB files regularly
drop from 16MB to 8 or 9MB.

Robert