D70/s RAW files (NEFs) are not lossless!


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unseen

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Dec 14, 2004
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#1
Hmmm I've always been told that RAW files are lossless...
Seems like I'm wrong. Stumbled across this about compressed NEFs

http://www.majid.info/mylos/weblog/2004/05/02-1.html
brief summary - loss of data in the shadow region due to lower resolution in quantizing data. Compresed NEFs are only capturing 9.4 bits of data as opposed to 12 bits of data.
Means: Loss of shadow detail.
The maths and the mechanical and technical details all works out, though I've not gotten my hands on any coding to verify, but this guy seems solid enough.

subsequently did a few searches.. and this:
http://www.robgalbraith.com/bins/multi_page.asp?cid=7-6269-6285-6288
As with previous Nikon digital SLR models, Nikon describes the compressed RAW setting as numerically lossy but visually lossless. Translated, that means the RAW data after compression is not numerically identical to the RAW data before compression: some picture information has changed. Like a low-compression, high-quality JPEG setting, however, Nikon is promising that it will not be possible to see the data loss.
OK I know this may not be news to some of you, but hey it's definitely news to me. I've always been brainwashed to accept that RAW files are not lossy. I know most of you will say that you never had problems with compressed NEFs, but I think should stop with the "all RAW files are lossless" thing.
 

unseen

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#3
ya. I read that. Apparently he's the only one going around saying that.
Ken Rockwell has said himself to be non technical, more of a artist than anything else.

I'm just pointing out something that someone has shown in actual fact rather than stating it based on general knowledge.

I rem there was one article stating that uncompressed NEFs preserve highlights much better than uncompressed NEFs for a D200, I just gave it a pass. Now I sorta link back to it.. it does makes sense..

Perhaps one day we find someone with a D200 and we take some photos with extreme dynamic ranges and we can compare.

but regardless, haha we should just shoot shoot shoot.. :)
 

unseen

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#5
LOL nothing wrong with shooting in compressed NEFs. For me RAWs are great fun to work with, though not if there's like tons of them..
I just want to point out that shouldn't say RAWs are lossless..
 

Jul 31, 2005
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Bt Batok
#6
unseen said:
LOL nothing wrong with shooting in compressed NEFs. For me RAWs are great fun to work with, though not if there's like tons of them..
I just want to point out that shouldn't say RAWs are lossless..
did nikon ever claim tt nef is lossless?
 

Watcher

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#8
roti_prata said:
did nikon ever claim tt nef is lossless?
The exact word from the manual, IIRC, is "virtually lossless". Others had already experimented and found that it chops off about 2-3 bits at the highlight ends as the eye is not uniformly sensitive to brightness.
 

unseen

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#9
roti_prata said:
did nikon ever claim tt nef is lossless?
???
Why is Nikon in the picture? I'm clearing up the misconception that RAW files (as in, a generalization) are NOT lossless, and that raw files do NOT automatically provide you with 12 bits of data.

it's more like MOST RAW files are lossless and provide you with 12 bits of data.

:) LOL moral of the story: Get the D200 and shoot uncompressed NEF!
 

Jul 31, 2005
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Bt Batok
#10
u said:
unseen said:
Compresed NEFs are only capturing 9.4 bits of data as opposed to 12 bits of data.
Means: Loss of shadow detail.
tts y i ask if nikon ever claimed its lossless
 

#11
unseen said:
http://www.majid.info/mylos/weblog/2004/05/02-1.html
brief summary - loss of data in the shadow region due to lower resolution in quantizing data. Compresed NEFs are only capturing 9.4 bits of data as opposed to 12 bits of data.
Means: Loss of shadow detail.
The maths and the mechanical and technical details all works out, though I've not gotten my hands on any coding to verify, but this guy seems solid enough.
What have you been reading? ;)

The loss is in the highlights, not in the shadows.
 

idor

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#12
reflecx said:
What have you been reading? ;)

The loss is in the highlights, not in the shadows.
just wondering..... is there any details in highlights to begin with?:think:
 

Jul 31, 2005
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Bt Batok
#13
idor said:
just wondering..... is there any details in highlights to begin with?:think:
good point:thumbsup:

is it possible to darken highlights the way we brighten shadows?:dunno:
 

unseen

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#14
oops, heh ya it's the highlights. Sorry, guess I was sleeping..

Of course there are details in the highlights. Highlights simply refers to the lightest portions of a photograph or halftone, as compared to midtones and shadows. It's a mistake to take it as the absolute region where total loss of details are lost.

If you care to read more about it:
http://www.adobe.com/digitalimag/pdfs/ps_workflow_sec2.pdf

This simply shows the amt of data loss from 12 bits to 10 bits in the highlight region.
http://www.normankoren.com/digital_tonality.html

From 2048 levels (12 bits) in zone 1 to 512 levels (10 bits).

You can get more details back from highlights than from shadows. As long as they're not washed-out.

Well, don't take my word for it. In RAW, go over-expose a photo by 2 stops, and take the same by under exposing by 2 stops.
Whatever it is, you will get comparatively more details back rather than the under exposed one (across the entire image).
 

hwchoy

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#15
the main practical difference between lossy JPEG and lossy RAW, is that you operate and save JPEG files, each time incurring more and more quantisation and compression errors, while you never operate on and save your RAW files.
 

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