Overexposing V Underexposing

Started Feb 10, 2013 | Discussions
nixda
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to Mark Weston, Feb 12, 2013

Mark Weston wrote:

With my X100, I shot DR100 and raw. I am waiting for my X100S to play with the Fuji parameters again, but this topic confuses me. It really seems like the Fuji DR settings are doing the opposite of expose to the right by underexposing and lifting the shadows instead of exposing to the right and bringing the highlights back. If I am understanding this correctly, I will likely stick with DR100 and use the histogram.

It is confusing. And it's not clear whether the camera is underexposing or overexposing until you look at the images later in a RAW converter.

Let's assume a given scene has a dynamic range of 10EV, from zero (black) to 10 (white). Let's also assume that the sensor is capable of capturing this scene without blowing any highlights. The JPG format can't accommodate the full amount of data, so the engine chooses what it thinks needs to be retained, guided by user-selected processing options.

Let's now say, the resulting JPG contains data in the range from zero (black) to 8EV (white). Thus the top 2EV are blown, i.e., anything that in the raw data falls into the 8-10EV range is now 8 and white.

Looking at the JPG, one would get the impression that one overexposed the shot, but in reality, the shot is 'overexposed' only with respect to the JPG conversion. The raw data do not contain any blown highlights.

Enter DR400. The camera now takes into account that the JPG conversion will likely blow highlights and adjusts the exposure such that that won't happen. In our example, the dynamic range of the scene is now no longer 0-10, but it is 0-8, which the JPG format can handle. If you now looked at the raw data, you'd conclude that the image was underexposed.

So, an image could be perfectly ETTR in its JPG version while at the same time being underexposed in its raw version. Likewise, an image can be perfectly ETTR in its raw version, but then, very likely, the ooc-JPG version will have blown highlights, and only some different tone mapping in post processing will preserve those, if desired.

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Mark Weston
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Thank you nixda
In reply to nixda, Feb 12, 2013

Good information in your post. Another thread on this topic also explains that DR400 with ISO 800 is actually be shot at ISO 200 resulting in the -2EV. I feel like I am starting to get a better handle on how this is working. I will need to experiment to see when/if settings are appropriate for what I am attempting at the moment.

http://www.markwweston.com

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baobob
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to nixda, Feb 12, 2013

So, an image could be perfectly ETTR in its JPG version while at the same time being underexposed in its raw version. Likewise, an image can be perfectly ETTR in its raw version, but then, very likely, the ooc-JPG version will have blown highlights, and only some different tone mapping in post processing will preserve those, if desired.

In my understanding ETTR should be done only for RAW (see the original LL refrence I gave in this thread) with DR 100 and no settings for shadows and highlights apart 0 which means no attempt in camera change of tonal curve

The absence of a complete histogram however does not help

It could be intersting to check if RAW ETTR does give better results than JPEG OOC with DR200 plus shadows and highlights - 1 or 2

If I get time I'll try it and report

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Indulis Bernsteins
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to Trevor G, Feb 12, 2013

And it would be much easier to get better results if our Fujis had proper RGB histograms.

I am surprised there is such little support for my request for the feature:

http://forums.dpreview.com/forums/thread/3379160

I show some graphic examples of the problem and solution.

Trevor- I agree! The "white" histogram can often be misleading and cause more problems than it is worth.

I don't think many people "get" that t he white histogram is the sum of R+G+B pixels. But that if one colour channel (R or G or B) is overloaded/peaked out, the white-only histogram shows "all OK"!

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nixda
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to baobob, Feb 12, 2013

baobob wrote:


So, an image could be perfectly ETTR in its JPG version while at the same time being underexposed in its raw version. Likewise, an image can be perfectly ETTR in its raw version, but then, very likely, the ooc-JPG version will have blown highlights, and only some different tone mapping in post processing will preserve those, if desired.

In my understanding ETTR should be done only for RAW (see the original LL refrence I gave in this thread)...

Yes, but most people (I would presume) attempt to do ETTR while using the in-camera JPG histogram as a guide.

with DR 100 and no settings for shadows and highlights apart 0 which means no attempt in camera change of tonal curve

As far as I can tell, the least biased settings are -2, not 0. -2 means no (or very little) of what the parameter is referring to. For example, sharpening -2 means no sharpening. It does not mean 'negative sharpening', i.e. blurring. Likewise for the other parameters.

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baobob
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to nixda, Feb 12, 2013

As far as I can tell, the least biased settings are -2, not 0. -2 means no (or very little) of what the parameter is referring to. For example, sharpening -2 means no sharpening. It does not mean 'negative sharpening', i.e. blurring. Likewise for the other parameters.

I was talking about setting of highlights and shadows, not sharpening. For these two the neutral setting is 0, see the detailed menu not the Qmand also read the DR page of the DPR review of the Xpro1

-2 for shadows pushes shadows where -2 for highlights reduces highlights and 0 sttings correspond to the native tonal curve at a given DR setting

You are right for sharpening

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nixda
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to baobob, Feb 12, 2013

baobob wrote:


As far as I can tell, the least biased settings are -2, not 0. -2 means no (or very little) of what the parameter is referring to. For example, sharpening -2 means no sharpening. It does not mean 'negative sharpening', i.e. blurring. Likewise for the other parameters.

I was talking about setting of highlights and shadows, not sharpening. For these two the neutral setting is 0, see the detailed menu not the Qmand also read the DR page of the DPR review of the Xpro1

-2 for shadows pushes shadows where -2 for highlights reduces highlights and 0 sttings correspond to the native tonal curve at a given DR setting

You are right for sharpening

The way I look at it is that -2 of highlight preservation preserves the least amount of highlights, 0 a medium amount and +2 the maximum amount. Likewise for the shadows. So, the neutral setting would indeed be -2. As 'neutral' as the engine allows, anyway. If you look at the tone curves, I can see though where the notion of positive and negative comes from.

It's mostly semantics. And it's confusing people, because it's easy to assume that a negative setting actually takes something away. In this case, one could assume that -2 of highlight preservation actively sacrifices highlights, which is not really the case.

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baobob
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to nixda, Feb 12, 2013

The way I look at it is that -2 of highlight preservation preserves the least amount of highlights, 0 a medium amount and +2 the maximum amount. Likewise for the shadows. So, the neutral setting would indeed be -2. As 'neutral' as the engine allows, anyway. If you look at the tone curves, I can see though where the notion of positive and negative comes from.

Sorry, but ...you are wrong see below the page DR of DPR review :

Using -2 -2 is the blue curve

+2 +2 is the yellow brown curve

0 0 is the standard tonal curve

Cheers

Robert

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nixda
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Re: Expose to the Right vs DR Auto, DR200, DR400
In reply to baobob, Feb 12, 2013

baobob wrote:


The way I look at it is that -2 of highlight preservation preserves the least amount of highlights, 0 a medium amount and +2 the maximum amount. Likewise for the shadows. So, the neutral setting would indeed be -2. As 'neutral' as the engine allows, anyway. If you look at the tone curves, I can see though where the notion of positive and negative comes from.

Sorry, but ...you are wrong see below the page DR of DPR review :

Using -2 -2 is the blue curve

+2 +2 is the yellow brown curve

0 0 is the standard tonal curve

Cheers

Robert

It's all in the way one looks at it. Another way to look at it, is that the blue curve (-2) has the largest dynamic range. '0' next, then +2. -2 won't throw away anything, so it's the baseline, whereas both the 0 and +2 settings result in a loss of information. With respect to tonal curve, one can see 0 as the middle ground, but I think in terms of data loss that would not be correct.

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