Thank you for your response.

I realize that there will be no data loss of any sort to the original RAW file.

My concern is whether or not the synced edits (from the lossy DNG copy) would be the same as if you directly edited the original. In other words, would they both print the same?

I noticed right away when I created the lossy copy that the colors and/or tonal values looked slightly different. The lossy copy actually looked better on-screen than the original. This leads me to think that - like for JPEGS - some sort of algorythm has been employed which is doing a little editing on its own even before you do anything.

My motive in asking is that I'm editing really large RAW files in LR and the program just crawls along. If I could just keep DNG lossy copies in LR, and edit and print those, then I could speed things up a bit. One lossy DNG copy I made was only 18-MB as compared to the 40-MB original.

I also understand that Adobe may be planning in the future to do something like I'm describing on an automated (invisible in the background) basis to speed things up in LR for large RAW files. If so, I'd sure like to know how this would affect color and tone in a print.

Thanks for the article link on DNG. It sounds like it was wrttten just before LR4 shipped.

I've converted almost all of my NEF RAW files to DNG and have been doing this for a few years. This business of using lossy DNG copies is not something I'm planning on doing, especially after reading that article and the reduction of bit-depth for the lossy format.

I guess there's no inexpensive way for me to speed up LR other than to order a new system.

I can see a distinct difference between the DNG and the lossy DNG screen views. I suspect it has a lot to do with the individual shot. I've only tried one so far and it was a well-exposed outdoor daylight shot.

I don't think the metadata matters here. Nothing on the original was altered or edited before I saved it as a lossy DNG. But, 14-bit compared to 8-bit must have some impact on color and tone.

Andrew,

Thank you for your help.

I followed the article and used the Apply Image comparisons in PS CS5 between two files - the original NEF RAW (Target) and its LOSSY DNG COPY(set as Source). It shows that they are different since the target didn't turn completely gray (You can see a grayed-over image) and Levels didn't show a single vertical line for the histogram. I compared the original NEF to a copy of itself and got the expected results - solid gray target and vertical histogram line. I did the latter just to be sure I was following the directions correctly.

This obviously indicates that there are differences between the two files. What do those differences mean? Would a print made from lossy DNG not have the same colors as a print made from a RAW? Eventually I'll do a side-by-side print comparison, but I just wanted your opinion.

Andrew Rodney wrote:

 

This PDF explains how you can aid yourself in seeing the differences in two identical documents (pixel dimensions) with very subtle processing differences using Photoshop’s Subtract command:

 

http://digitaldog.net/files/Apply_Image.pdf

Andrew Rodney wrote:

 

It may mean nothing but at least you can now see where the data is different, you know there is a difference etc. I suspect you’ll not be able to see this any other way. It isn’t visible on screen, probably not on print. But by subtracting the two and using Levels, you can get some idea that there are differences and where visually in one image.

Thank you Andrew.