DNG looks different than NEF

[Jimi V]

I just started converting some D70s NEF files to DNG. The DNG files look about ~1/3 stop darker than the NEF originals, in programs like PhotoMechanic. Iview3. But not in RawShooter Premium.

I'm using DNG Converter 3.3x43 on XPsp2, fully patched.

Any ideas on what causes this?

Thanks fro any suggestions!

-Jimi

[peterkrogh]

DNG files have gone through Camera Raw and are rendered according to Camera Raw settings annd capabilities.  They will (almost) never look identical to NEF files that have not been through Camera Raw. 

Did you read the part of the book in chapter one about the benefits of DNG.  You might need to re-read it.
Peter

[Jimi V]

I'm expecting the book to arrive tomorrow. I'm really looking forward to jumping into it!

[dissolved]

DNG files have gone through Camera Raw and are rendered according to Camera Raw settings annd capabilities.  They will (almost) never look identical to NEF files that have not been through Camera Raw. 

I've spent the last day trying to get my head around differences between Raw, DNG, and TIFF.  My current understanding is both Raw & DNG contain the unaltered data captured by the sensor (almost always three incomplete channels of red, green, & blue).  An uncompressed TIFF, has merged those three channels into so that every pixel has a red, green, & blue value (as opposed to three seperate channels with "missing pixels").  Hopefully this understanding is more or less correct, if not complete.

What confuses me still, is why Camera Raw and DNG would look different, as suggested in this post.  If the DNG is suppose to preserve the three seperate incomplete channels originally captured by the sensor, then why does it look different than the Raw?  It seems to suggest that some conversion of the original data is in fact applied to the original Raw file.  Do you lose something by converting Raw to DNG?  I have read you can embed the original Raw file in a DNG, at which point I'm confused why I wouldn't just hold on to the Raw file itself.  I'm sure I'm still missing a subtlety.  Any help in understanding this would be greatly appreciated.

Thanks,
  Ryan

[peterkrogh]

Ryan,
Your general understanding is correct.
The NEF and the DNG could look different for several reasons.  First, you must determine what you are looking at.  Each has RAW data, and each has a preview JPEG put into the file.  (You can build a DNG with no embedded preview as well).

Some applications can display the preview, and some will display the rendered data.  If different applications are displaying the RAW data, they will always do it differently.

Please provide more details on where you are seeing the mismatch, and everything that was done to the files.
Peter

[dissolved]

I actually haven't begun working with Raw or DNG files yet, I'm still in the dark ages with TIFF... I wanted to understand Raw and DNG before I jumped in.  But, something you said made me see the light.  I think what I wasn't getting, was that it is impossible to display to a human anything useful from Raw without doing some sort of conversion.  In retrospect this seems obvious.  I wasn't understanding that even though it must do a conversion to display it, it still leaves the data untouched in the file (ie. still Raw).

I think I understand it all now.  Thanks.

[danaltick]

Ryan,

A camera sensor does nothing more than capture photons and perform a digital conversion on them.  Twice the photons means twice the light; hence, Raw data is linearly mapped.  However, the human eye (as well as the other 4 senses) do not sense linearly, but rather logarithmically.  Therefore Camera Raw applies a gamma function to the Raw data before presenting it to your display.  The histogram you see in ACR represents a gamma mapping of the Raw data after post-conversion to your selected output space (i.e. Adobe RGB, ProPhoto RGB, etc.).  If the histogram were to represent the actual linearly mapped data, it would be all squinched over to the left.  If you are aware of this, you can use it to your advantage because half the data always resides in the upper stop and the rest is in the lower five stops (for a six stop DSLR).  If you over-expose your shots by a stop or two, you can usually recover that upper stop in Camera Raw by pulling that data down into the mid-tone and shadow areas where the eye is much more sensitive.  This is actually one of the hidden powers of Raw that I think most photographers are unaware of.  If you think about it, that's half your detail being thrown away by not taking advantage of this feature.
I've elaborated probably more than necessary on your question, but if you are interested and would like to know more about the innards of Raw without getting heavy into the math, I learned most of what I know about Raw from this book http://thedambook.com/smf/index.php?topic=265.0.

Dan

[peterkrogh]

Dan,
Thanks for the nice synopsis.
Bruce's book is indeed mandatory reading for anyone trying to understand how RAW imaging works.

It's hard to get your head around this at first. 
With a TIFF, there is an objectively truthful way to render the file. With a RAW file, there is really only subjective interpretation.   
And RAW file rendering is rapidly developing technology.  This makes the "fixed rendering" of the embedded preview extremely important, since you will likely work on your RAW file collection with many different converters over time.
Peter

[danaltick]

Peter,

And what I've found is that I can create a really good DNG previews using Bruce's techniques.

Interestly enough, I attended my first wedding photography seminar a few days ago just to get my feet wet http://www.digitalwakeupcall.com/.  I was shocked to find out that David Ziser shoots JPEG.  It was a real awakening for me.  He had prints all over the room, and I must say they were staggering!  However, I believe it's possible to incorporate David's techniques into a Raw workflow using your DAM techniques with hopefully no loss in time.  I should be able to make up for the lost time through the use of Bruce's techniques in Camera Raw; thereby, shifting global adjustment work from Photoshop to ACR.  I will be delving into this some as time permits and therefore probably making some posts in the wedding thread.  I have a lot of material to go over from the seminar (not to mention his software apps http://www.davidziser.com/educational_materials.htm), but I want to add this component to my business repertoire in the near future.

Dan

[peterkrogh]

Dan,
You can definitely get outstanding results by shooting JPEGs.  But there are some caveats.

1. You have to get it perfect in camera.   If you don't then you will rapidly start to lose quality as you make adjustments to the files.  While the JPEG workflow is faster when things are perfect, you also begin to really chew up time if you have to make a lot of individual adjustments to JPEGs.

2. You need to have limited contrast in the subject matter.  Aside from nailing the exposure, you also need to be working with a scene that can be well represented by 8 bits.  If you have bright highlights and deep shadows and want to retain detail in both, then JPEG will start to really fall down.

Personally, I think the scales tipped toward RAW file workflow as being faster and more efficient with the release of CS2 and ACR/DNG 3.2.
Peter

[johnbeardy]

And since when was there limited contrast with a wedding dress in the heart of the action? That perfect moment might have blown highlights that are just about recoverable with raw. IOW I wouldn't think of shooting jpeg at a wedding and throwing away a big chunk of image data - it's a false economy. Being cynical, I'd probably end up with loads of auto bracketted shots and extra shots just to cover me for the lost beauty.

John

[danaltick]

John & Peter,

I do recall David saying that he does some bracketing for insurance, which can definitely lead to a large quantity shoot.  You both make some very valid points here.  Even for wedding work, I will stay with Peter's workflow, but will be using some of David's apps for the collaging and faster localized corrections that can only be done in Photoshop on the down-selected images.  I would expect that the majority of the images can be printed/delivered straight from the DNG previews, and only a small select few would actually need localized adjustments.

Dan