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Author Topic: Dynamic Range War  (Read 10476 times)

helpful

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Re: Dynamic Range War
« Reply #30 on: March 29, 2012, 03:25:00 PM »
I'd caution strongly against expose to the right

Expose properly, ideally with a well-calibrated incident meter.

If you've still got crushed shadows and blown highlights in critical areas of the image, you either need better light or you need to go to HDR -- and that's assuming that the crushed shadows and blown highlights are a problem in the first place...the kinds of photography where it's a problem but you can't either fix the light or use HDR are basically nonexistent.

Don't forget that there's a great deal more DR to be had in any well-exposed RAW image than what comes right out of the converter with the default settings.



Good points, and actually you have explained very well what the point of ETTR is, which is to maximize the potential of camera sensors, which are capable of far more than what is offered by default exposure settings. The camera sensors are so good that the dynamic range of most scenes is far within the maximum DR capabilities of the sensor. So photographers are faced with a question--use zero exposure compensation, or try to manually expose to get the most detail? Due to the way that data is recorded (2,048 bits of data for the right side in the brightest stop of light), there is much more data recorded on the right side of the histogram.

http://schewephoto.com/ETTR/index.html

There is an amazing example on that page which shows that the little tiny blip on the right side of the sensor (way, way, overexposed, and extreme ETTRing) actually has as much image detail as almost the entire image histogram. That's not what anyone should do. The point is just to show how much more data and details are being recorded for any part of the image that is on the right side of the histogram, compared to the left.

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Re: Dynamic Range War
« Reply #30 on: March 29, 2012, 03:25:00 PM »

TrumpetPower!

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Re: Dynamic Range War
« Reply #31 on: March 29, 2012, 04:05:44 PM »
http://schewephoto.com/ETTR/index.html

There is an amazing example on that page which shows that the little tiny blip on the right side of the sensor (way, way, overexposed, and extreme ETTRing) actually has as much image detail as almost the entire image histogram. That's not what anyone should do. The point is just to show how much more data and details are being recorded for any part of the image that is on the right side of the histogram, compared to the left.

Actually, that page is an excellent example of why not to do ETTR.

Look at the three adjusted histograms. Notice that tall spike on the right on the rightmost histogram? See how it's the only part of the histogram significantly different from the other two? And how it goes all the way to the top?

Even though that spike isn't all the way at the right edge, it still represents saturated, blown-out pixels. All that's happened is that ACR has uniformly reduced the blown pixels to a still-uniform value less than maximum.

Sure, the shadows are cleaner. But I bet a 100% crop of that ``Prairie'' sign would show much more detail in the properly-exposed version than the overexposed one. Were that a wedding dress, Mr. Schewe's smartypants exposure hijinks would just have made the mother of the bride very angry indeed. Even though his histogram showed a "good ETTR" exposure.

And have a look at the waterfall, too. Sure, he was able to recover a good amount of tonality, but the colors are posterized to a ridiculous extent. That exact same sort of posterization is going on in all the other overexposed highlights, with the degree of posterization proportional to the amount of overexposure.

In other words, using ETTR means all your specular highlights will be either devoid of color or have that same sort of severe posterization. Now, granted, the definition of specular highlights is that they get blown...but they'll be much bigger in area and the transition from colorful to blown will be much more abrupt and less colorful. You're basically taking a sledgehammer to your specular highlights, when they really should (in my opinion) remain light and delicate.

By all means, if you like the ETTR look, especially if you're shooting sleeping black cats at the bottom of a coal mine, go for it. But, when that cat wakes up and you want to capture the glint of the candlelight in her eye...use ETTR if you want the glint to be a hard-edged white outline, and expose properly if you want it to look like a candle flame.

Cheers,

b&

sarangiman

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Re: Dynamic Range War
« Reply #32 on: March 29, 2012, 05:19:41 PM »
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* Current DSLRs are in the 10-12 stop range. (Note: the newest FF bodies from Canon and Nikon haven't been tested yet.)

* Print film has 9-14 stops depending on emulsion.

dtaylor: Print film is more forgiving, yes, but I've always found it hard to compare the stops of DR in print film vs. digital b/c it boils down to: how much noise are you willing to accept in the shadows? If you look at Roger Clark's treatise on DR (http://www.clarkvision.com/articles/dynamicrange2/), negative film falls apart so quickly that its acceptable DR is significantly lower than that of even earlier generation DSLRs & almost on par w/ some slide films (though with Velvia, e.g., the actual signal is very low so that, even with lower noise, it may be hard to extract that signal without a drum scanner). However, latitude with slide film is terrible; I'm always afraid of clipping shadows or blowing highlights. With negative film, I overexpose a sunset by 3 stops & still retain color around the sun. But the shadows are still starving for exposure & are just obliterated by noise! For example, here's a shot overexposed by 2 2/3 stops (as compared to what Evaluative Metering thought the exposure should be on a EOS-3):



Ektar did well, considering the DR of the scene (the sun is still high up in the sky). But those rocks are incredibly noisy upon closer inspection.

So it's my opinion that your estimation of the DR of negative film is highly dependent upon your subjective opinion of acceptable SNR in the shadows.

Which is why DXO attempts to standardize measurements by setting that acceptable SNR to 1 in their measurements. But, like you, I have my doubts of DXO measurements when they claim the D800 has 1.4 stops more DR than the D4, normalized or not. At a pixel level (not normalized), DXO claims 13.24 stops DR for the D800, but only 13.1 stops for D4 normalized (so, less at the pixel level). That just doesn't make any sense.

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True, but print film quickly fell apart on the shadow side.

Exactly. You said it yourself :)

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"For Maximum S/N Ratio [i.e., image quality]

"The simple lesson to be learned from this is to bias your exposures so that the histogram is snugged up to the right, but not to the point that the highlights are blown.

Agreed, but this brings up another issue I've had with most RAW converters/image processing software I've had for a while -- when you ETTR, even without blowing out channels, you quickly desaturate bright regions like skies. Software doesn't make it easy for you to recover those tones, which is why I've often found myself being careful about how much I ETTR when I want saturated skies in my final photo. Lightroom 4 is changing that with their 'highlights' & 'whites' slider, which now allow you to really pull back color/tones from bright regions of your photograph. Aperture/Photoshop has allowed you to do this, with limited ability, with their 'Highlights/Shadows' tools for some time now... but I never found it to be enough or as good as LR 4 now.

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Where the DR limitations come in, shadows at low iso, is NOISE.
When you start to brighten those shadows you may also start to see more chroma noise show up in those areas.  If the noise is random it's more acceptable and easier to minimize its appearance.

If the noise has a pattern to it, banding, cross-hatching or similar, then it's very difficult to impossible to remove the appearance of this noise.

This is where the Canon vs Sony-Nikon sensor argument arrises.
One company's sensors have more pattern noise at low iso shadows than the other company's, thus limiting the ability to boost shadows and achieve an effective HDR image from one exposure.

EXACTLY. Thank you for concisely stating the reason why some of us care about banding in so-called 'useless shots taken with the lens cap on'.
« Last Edit: March 29, 2012, 05:22:55 PM by sarangiman »

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Re: Dynamic Range War
« Reply #32 on: March 29, 2012, 05:19:41 PM »