DRO and RAW underexposure

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Cecco
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DRO and RAW underexposure

Unread postby Cecco » Sun Jul 20, 2008 1:16 pm

David,

a while back you mentioned in an article on photoclubalpha, the A700 would underexpose the RAWs, when DRO is enabled.

Being a RAW shooter I found it disappointing that this meant, DRO was unusable for me. Luckily I've did my own experiments with RAW+JEPG a while back and to my surprise couldn't see a difference in the RAWs with DRO on or off. I've started a thread on DPR asking others about their experience, but unfortunately no-one seemed to have done his own tests.

Afterwards the story of DRO underexposing the RAWs appeared in several threads on DPR and quite some other forums (even German ones) and even Garry Friedman gave a reference to it in his A700 ebook. I've replied to each of them asking, whether the poster tried it himself or just quoted from your article and no one ever stated, he had seen the underexposure himself. Meanwhile some others did their own test and confirmed my observation, that the RAWs were absolute identical with DRO on or off. Since then I started to disbelief your DRO RAW underexposure theory and called it one of the most believed myths of the A700.

David, I would have liked to see you participate in one of these threads on DPR, and actually invited you via email to one a while back. As you are banned on DPR now, this is not possible. Thus I open this thread on photoclubalpha to discuss your theory here.

May I start with a reply I've given to one of the last threads about this on DPR:

> However, the fact is that DRO CAN cause the RAW to be underexposed,
> and David's example shows that. In order for DRO to work, in some
> circumstances it will underexpose the shot as with his first example.

Yes the RAW in David's example is underexposed. But I have a problem with David's conclusion, it is DRO that is the reason for this. He didn't take the same scene with DRO off (at least he didn't say so). He just assumed, the RAW would have been exposed differently with DRO off.

But look, there are these bright windows in the background. Couldn't they have thrown-off metering and led to the underexposure, whether DRO was on or not. David might have been mislead to held DRO responsible for the underexposure, because it fitted nicely into his theory. It is always dangerous to derive a statement without having tested it thoroughly.

When we speak about underexposure, we must differentiate between a technical underexposure, i.e. the camera exposes less than it would do without DRO enabled, and the perceived underexposure, the scene looks too dark to our eyes.

Both the RAW pictures of David and William show a perceived underexposure. You need to dial in +EV when shooting to make them look good and you probably won't do this with DRO on, because the preview and histogram give you the impression, the perceived exposure is correct.

So yes, DRO could lead to an underexposed RAW, because it might trick you in not overriding automatic exposure with +EV, like you would do normally.

But no, DRO doesn't change automatic metering on the RAW in a gain-based way, like David assured in his article.

Or in other words: It is not the camera but the photographer, who is responsible for a possible underexposure with DRO on.


Shooting RAW+JEPG is the only alternative for a RAW shooter to use DRO. My impression is, that a lot of A700 users stay away from using DRO with RAW+JEPG solely because of your article, which would be sad, if the facts don't hold true. And so far no-one including myself was able to find a proof for your theory.

I'm really interested, whether you investigated more into this question after your initial article and whether you know of a reproducible setup to show the DRO RAW underexposure.

Cecco

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Re: DRO and RAW underexposure

Unread postby David Kilpatrick » Sun Jul 20, 2008 1:49 pm

On the A200, 300, 350 DRO does not affect the RAW exposure significantly (no more than using Hi200 did on the A100). On the A700, using DRO Advanced with manual settings certainly does affect the raw exposure - on subjects where no over-ride would be needed, it is always kept to a minimum. Using DRO in its normal and Automatic modes does not appear to have any effect on exposure or the density of raw files.

Nikon specifically warn the their manual that when using their own D-Lighting Advanced mode, raw files will be dark. The principle is exactly the same, and I found out about the dark raw files before reading the Nikon manuals for the D300/60/3. Sony does not issue any warning.

I do not use DRO for exactly the reason you don't want to - I need raw files to be fully exposed. However, for certain jobs I use it - always for flash shots of presentations, groups etc indoors. It is a one-stop solution for perfect JPEGs.

David

Cecco
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Re: DRO and RAW underexposure

Unread postby Cecco » Sun Jul 20, 2008 2:45 pm

On the A700, using DRO Advanced with manual settings certainly does affect the raw exposure - on subjects where no over-ride would be needed, it is always kept to a minimum.


David,

I shot with DRO+ manual up to level +5 and the RAWs were absolute identical. Does your A700 behave different from mine?

Did you do tests with an identical scene, that shows the different exposure with DRO on/off? Or do you just have the feeling, your RAWs look a bit less exposed, if you have DRO+ Lv x on?

I do not use DRO for exactly the reason you don't want to - I need raw files to be fully exposed. However, for certain jobs I use it - always for flash shots of presentations, groups etc indoors. It is a one-stop solution for perfect JPEGs.


I look at DRO in combination with RAW+JPEG more as a first-stop solution to save time in PP for the less important shots. If the DRO-JPEG is fine, I don't fiddle with the RAW, if it sucks or I think I can do better by processing the RAW, I resort to the RAW.

But that works only, if the RAW is not compromised by DRO. Finding out the truth about this is the whole point of this discussion.

Cecco

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Re: DRO and RAW underexposure

Unread postby David Kilpatrick » Sun Jul 20, 2008 7:09 pm

What raw processor are you using, and are you enabling any auto settings?

If you use Sony IDC, the raws will appear identical to the JPEG once they have all loaded. If you set auto adjustments in ACR, they will also look identical. In many applications, you never see the raw file as a thumbnail (ever) you see the embedded JPEG - which is the DRO+ processed image, so the raw file will look identical to the JPEG every time. The only way to see the actual density of the raw file is to use ACR and turn off all adjustments.

I have not tested to see whether different levels of DRO+ Manual produce different raw densities. Of course, if you shoot a picture which does not need DRO+, like a grey target or an average scene, there will be no effect as DRO will not be used. It is intelligently linked to the multi-segment metering, and the two interact. Where DRO+ must have a strong effect, the metering ensures that the image is exposed for the highlights and ignores the focus point, which normally determine the bias of the exposure.

While Nikon's system is not based on Apical technology, it is very close to it, and they originally used Apical's chip. The D700 I am testing now has come without the full instruction manual, which is annoying, or I could quote the footnote which carefully (in small print) warns users about the reduction in exposure given when using their process under certain conditions.

My examples in my DRO article:
http://www.photoclubalpha.com/2007/11/0 ... ic-bullet/
use minus compensation as well in the first case, and also show accidentally underexposed shots rescued by DRO - no-one is suggesting that DRO will underexpose an raw file by this degree.

Like Nikon, the suggestion is just that the raw file will probably be underexposed by an amount depending on the tones and metering. This is one of the reasons why you can't use DRO with spot metering, centre weighted metering or manual exposure. It is also part of the reason why DRO+ files are noisier than regular shots, they rely on boosting underexposed values, not on recovering headroom from normally exposed images.

This is nothing new. The Hi200-250 setting on the A100, A700 is actually just the sensor left at ISO 100 (it may actually be at ISO 125 or 160 - it does not seem to be as low as 100, and there is a suggestion that the native sensitivity is a little higher and 100 is a 'saturated' sensitivity), but the exposure set as if the gain was at ISO 200 or 250, and a special curve applied to lighten the midtones leaving the highlights unaffected. If you shoot RAW when using the Hi settings, you get an underexposed raw file. DRO+ seems to work in almost exactly the same way, but applies Iridix processing instead of a CTF curve.

David

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Re: DRO and RAW underexposure

Unread postby alphaomega » Tue Aug 19, 2008 2:43 pm

I have just joined and have found this thread most interesting. I kept wondering why my RAWs taken with my A700 were so much darker than those from my R1 latterly. They looked OK in Bridge initially, but when I then clicked on the image it went dark by at least a stop and the same in ACR needing something like 50% Brightness adjustment plus often a dose of Fill Light. I had left DRO level 3 on even shooting RAW assuming it would have no effect. I have now disabled DRO and will await results when next the weather obliges. I also noticed more noise in shadows than I would expect at my favourite ISO250 setting. I will report my findings when some new images are to hand. This seems to tie in with David's findings.
John Peter

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Re: DRO and RAW underexposure

Unread postby Dr. Harout » Tue Aug 19, 2008 5:18 pm

I was not aware of such a discussion, but a few days ago I made a shot of my garden just to see the effect of DRO. Actually I had set my A700 to DRO off.
So took one picture like that and the next one with just activating the DRO (i.e. to standard), and to my surprise the latter was underexposed (viewed on my camera LCD). Thought it was from the LCD, but when opening with ACR 4.5 I realized that there is a difference and thought this is how it should be, till I saw this discussion.
Parameters of ACR 4.5 I have set to predefined for all pictures, so they open with same levels regardless of exposure.
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