Importing DNG Files

[brentwilson]

I have a Pentax K2''D camera. I have recently been shooting DNG raw files. But I am not sure what which of the import options is best to import them and what exactly the different options mean.

For example, with one particular picture my options include the following:

- If I select "Copy photos to a new location and add to catalog" the DNG file is copied over from my camera and is 16.1 MB in size.

- If I select "Copy photos as Digital Negative (DNG) and add to catalog" then the DNG file from my camera is apparently compressed and results in a dng file that is 7.7 MB.

So, I am wondering which option is better and why. What is the real difference between these two options? In my Lightroom Import preferences, under "Import DNG Creation" I have selected the Medium size JPEG Preview, "Preserve Raw Image" as the Image Conversion Method, and under options the "Compressed (lossless)" box is checked and so is the "Embed Original Raw File" box.

I would appreciate any advice and information that can be offered. Thanks!

 

[Victoria Bampton]

Hi Brent, welcome to the forum!

I'm not familiar with the DNG's from a Pentax, however a quick look at the specs suggests it 1'mp? In that case, I'd guess your camera is also embedding a full size preview, giving you a 16.1mb filesize. When LR's converting to DNG, it's likely downsizing that preview to your Medium size jpeg preview set in preferences, and compressing the data more efficiently.

Personally I'd do a few tests:
1. Try it with 'preserve raw image' and 'embed original raw file' turned off, and see if that has any effect on file size.
2. Try it with a full size high quality preview and see what effect that has on the file size.
3. Try it with compression turned off, and see what effect that has on the file size.

Having done that, you'll have a much clearer idea about the difference in file size.

 

[brentwilson]

Thanks for the help. Yes, my camera is about 1'.2mp.

I experimented a little bit. I kept the "preserve raw image" setting, rather than having it convert the pictures to linear images.

I bumped the JPEG preview from medium to full-size. That bumped the compressed dng file size from 7.7 to 8.6 MB.

The "imbed original raw file" option doesn't seem to make a difference. I am guessing that only takes effect if my original raw files are in a proprietary format. But mine are now shot in DNG right in my camera.

The big difference seems to be whether or not I check the "Compressed (lossless)" box in Lightroom preferences. With that unchecked, the imported file sizes are several MBs larger than the original raw files. With the box checked, the compressed files are about 8.6 MB with the full-sized jpeg preview option selected.

So I guess the question is this... what is the real effective difference between selected the "compressed (lossless)" option and not selecting it. Are the compressed files just as useful and do they still contain all the data of the non-compressed files do? Will these compressed dng files continue to be compatible with photo software in the coming years and decades? Or would the non-compressed dng files have a greater longevity when it comes to compatibility and usability?

 

[Mark Sirota]

The losslessly-compressed files contain all of the original data, and I doubt there's any difference in longevity or compatibility.

The tradeoff is disk space and I/O performance vs. CPU power and memory. With compressed files, anytime you want to do anything with it, it has to be retrieved from disk and decompressed before it can be used. However, there's fewer bytes to store, fewer bytes to back up, and fewer bytes to read off the disk when you want to make use of the files.

You could do some tests to determine which is faster on your system today, though it's possible that future systems you might own might prefer it the other way.

 

[ttk]

Use select "Copy photos as Digital Negative (DNG) and add to catalog" then the DNG file from your camera will then be compressed and results in a dng file that is 7.7 MB.
I use this for my Pentax K2'D and convert my 23mb DNG files down to 11mb approx, this works very well for lightroom, if you want to use the full DNG as in Camera edit in Adobe Camera Raw in Photoshop.
Hope this helps..

 

[brentwilson]

Thanks everyone for your advice. I appreciate it!!!