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Author Topic: Michael Reichmann, ETTR and Oly OMD EM5  (Read 22061 times)
richarddd
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« Reply #20 on: January 02, 2013, 08:55:50 PM »
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@Vladimirovich, regarding shot noise and DR, I was trying to figure out if there were measures other than read noise that might be relevant. Shot noise isn't relevant, as you say, because we are assuming a fixed exposure. DR shouldn't be an issue if we're below highlight clipping.

Regarding available tools, are we communicating somewhere else? I haven't posted here about ETTR and the E-M5. In any event, others on this forum might be interested in the answer.
« Last Edit: January 02, 2013, 09:00:56 PM by richarddd » Logged

Vladimirovich
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« Reply #21 on: January 02, 2013, 09:14:52 PM »
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Shot noise isn't relevant, as you say, because we are assuming a fixed exposure.

it is relevant, you just can't increase SNR (signal vs shot noise, which is the dominant component beyond dark shadows) by increasing exposure... and your question is, if I understand it correctly, what else can you do to make your data better... the only noise that you can reduce are the noise because of the temperature and because of charge readout/ADC circuitry... hence cool your sensor/circuitry and/or try to play w/ gain increase (in you do not clip)...

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« Reply #22 on: January 03, 2013, 12:12:22 AM »
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Increasing ISO is a bad idea. The reason behind ETTR is to maximize exposure. You want to capture as many photons as possible.

That's my understanding of ETTR as well.  As far as I'm aware, ETTR refers to increasing exposure to make use of unutilized sensor DR.  If you shift the histogram to the left to protect highlights...that's not ETTR.  Sure, you may be trying to get those highlights as far right as possible without clipping, But ETTR specifically refers to setting an exposure greater than Standard Exposure for the expressed purpose of reducing noise.

With that as a definition, I'm quite certain that increasing ISO provides no benefit.  The reason is that exposure is reduced in post processing...not increased.

There have been images demonstrating that some cameras produce better results at high ISO.  This is done by taking ISO 1600 or ISO 3200 images (and sometimes increasing exposure on those by a few stops) and comparing to images taken at ISO 100 or ISO 200 and then increasing exposure in post by 5 EV or more.  The reason that these examples give the results they do is that the difference in noise (of which there really is less of at the higher ISO settings) is amplified by the boosted exposure.

But with ETTR, exposure isn't increased in post...it's reduced.  And when you reduce exposure, some of the bits representing the improved noise levels will simply be chopped off.  So whereas the noise difference in those "proof of concept" images was boosted into the sunlight, any real noise difference in actual images will be suppressed into obscurity by the application of negative EC.

No one's been able to show me a pair of images demonstrating improved noise via ETTR with elevated ISO levels.  If anyone has some I'd be interested in seeing them.  But until then, I have to agree with those who say ETTR only valid at base ISO.
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Vladimirovich
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« Reply #23 on: January 03, 2013, 01:27:28 AM »
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OP has limits on exposure time and aperture and provided that raw data is not clipped in his situation the question is - whether it makes sense to increase the gain in camera... he can't get more light (remember - no increase in exposure time or aperture), can he get somewhat less noise... the answer is - yes, he can, by increasing the gain (in some cameras, up to a certain limit, provided that he is not clipping raw data or otherwise getting close enough to the saturation capacity which may /or may not/ be not good for some cameras) reduce the read noise... what's wrong w/ that ? he can't get bigger SNR by getting more light under his conditions, he might get bigger SNR in shadows by getting less read noise.
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richarddd
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« Reply #24 on: January 03, 2013, 05:07:57 AM »
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No one's been able to show me a pair of images demonstrating improved noise via ETTR with elevated ISO levels.  If anyone has some I'd be interested in seeing them.  But until then, I have to agree with those who say ETTR only valid at base ISO.
See reply #1 in http://www.luminous-landscape.com/forum/index.php?topic=56906.0 (the link was posted in reply #16 to this thread)  The photos were taken with an older Canon, but I believe the E-M5 has the same behavior.
« Last Edit: January 03, 2013, 05:11:10 AM by richarddd » Logged

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« Reply #25 on: January 03, 2013, 07:20:05 AM »
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See reply #1 in http://www.luminous-landscape.com/forum/index.php?topic=56906.0 (the link was posted in reply #16 to this thread)  The photos were taken with an older Canon, but I believe the E-M5 has the same behavior.
Please reread my post.  This is exactly the type of "proof" I was referring to.  The image taken at ISO 100 had its exposure increased in post to match the image taken at ISO 1600.  That is not what happen in the ETTR method.  ETTR does the reverse...an overexposed image has its exposure reduced in post.  In the "proof" the noise difference is amplified.  With ETTR the noise difference is diminished.

The EM-5 has a sensor made by Sony, and typically the latest Sony sensor don't exhibit this behavior.  The EM-5's SNR is curve at DxOMark doesn't seem to indicate that it does, so I would be surprised if the EM-5 behaved this way.
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richarddd
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« Reply #26 on: January 03, 2013, 08:05:19 AM »
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Please reread my post.  This is exactly the type of "proof" I was referring to.  The image taken at ISO 100 had its exposure increased in post to match the image taken at ISO 1600.  That is not what happen in the ETTR method.  ETTR does the reverse...an overexposed image has its exposure reduced in post.  In the "proof" the noise difference is amplified.  With ETTR the noise difference is diminished.

The EM-5 has a sensor made by Sony, and typically the latest Sony sensor don't exhibit this behavior.  The EM-5's SNR is curve at DxOMark doesn't seem to indicate that it does, so I would be surprised if the EM-5 behaved this way.
My posts are about setting exposure and wondering if increasing ISO to just below the clipping point will help image quality. Exposure is set at the maximum consistent amount with desired blur (or lack of) and DOF.  

The photos I posted show increasing ISO decreases noise.

Is your post responsive to the question of whether holding exposure constant and increasing ISO (up to say 1600) will improve image quality for the E-M5?

In your post, you agree that "Increasing ISO is a bad idea. The reason behind ETTR is to maximize exposure. You want to capture as many photons as possible."  As increasing ISO does not change the number of photons captured, why is increasing ISO a bad idea?

The usual reason increasing ISO is a bad idea is that it is often associated with decreasing exposure, which is a bad idea. That's not an issue here; we're holding exposure constant.
« Last Edit: January 03, 2013, 08:09:58 AM by richarddd » Logged

Vladimirovich
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« Reply #27 on: January 03, 2013, 08:44:05 AM »
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The EM-5 has a sensor made by Sony
it does not.
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Vladimirovich
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« Reply #28 on: January 03, 2013, 08:48:14 AM »
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The EM-5's SNR is curve at DxOMark doesn't seem to indicate that it does
and we are not talking about SNR @ 18% which is what DxOMark curve shows... @ 18% it is dominated by shot noise... we are talking about shadows (deep) and read noise reduction... there the relevant curve is DR curve (non Sony looking curve by the way... it is Panasonic curve).
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« Reply #29 on: January 03, 2013, 09:37:25 AM »
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That's my understanding of ETTR as well.  As far as I'm aware, ETTR refers to increasing exposure to make use of unutilized sensor DR.  If you shift the histogram to the left to protect highlights...that's not ETTR.  Sure, you may be trying to get those highlights as far right as possible without clipping, But ETTR specifically refers to setting an exposure greater than Standard Exposure for the expressed purpose of reducing noise.

With that as a definition, I'm quite certain that increasing ISO provides no benefit.  The reason is that exposure is reduced in post processing...not increased.

...

I was under the impression that there were two benefits to ETTR.
1) as you say increase signal to noise ratio.
2) Place the signal you have into the right half of the histogram where you have more exposure gradations, ie higher sampling rate. 

In the case of #1, there is no benefit to increasing ISO as the OP mentions.  In these case of #2, there is a small benefit because after normalization of the tone curve, it may reduce the effect of posterization.

 
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« Reply #30 on: January 03, 2013, 09:59:00 AM »
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it does not. [have a sony sensor]

A few months ago there was news that the president of Olympus had stated that the EM-5 sensor is made by Sony.

http://www.imaging-resource.com/news/2012/07/06/olympus-ceo-identifies-sensor-supplier-for-flagship-mirrorless-camera

Unfortunately, the link to the original story at Yahoo Japan no longer works.  However, Sony DID invest some 645 million dollars in Olympus at the end of September, and if Sony wasn't supplying sensors to Olympus previously, it definitely is going to do so, as that fact was already announced in October...
http://www.43rumors.com/olympus-and-sony-conference-in-tokyo
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« Reply #31 on: January 03, 2013, 10:18:20 AM »
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My posts are about setting exposure and wondering if increasing ISO to just below the clipping point will help image quality. Exposure is set at the maximum consistent amount with desired blur (or lack of) and DOF. 

The photos I posted show increasing ISO decreases noise.

Is your post responsive to the question of whether holding exposure constant and increasing ISO (up to say 1600) will improve image quality for the E-M5?

In your post, you agree that "Increasing ISO is a bad idea. The reason behind ETTR is to maximize exposure. You want to capture as many photons as possible."  As increasing ISO does not change the number of photons captured, why is increasing ISO a bad idea?

The usual reason increasing ISO is a bad idea is that it is often associated with decreasing exposure, which is a bad idea. That's not an issue here; we're holding exposure constant.

If you decrease ISO, then you can increase exposure with a slower shutter or wider aperture.  If you have a shutter and aperture limit, then you can't really perform ETTR, as the goal of ETTR is to maximizing your signal.  Sure, you can increase your ISO to push the histogram to the right...but your exposure will always be less than optimal.

As to whether you get any benefit from pushing the histogram to the far right via ISO, as I said I believe there is no benefit.  The reason is that the process of applying negative EC to correct the exposure will likely wipe out any gains in reduced noise.  Those gains are in the least significant bits of data, and those are the bits that get dropped when you apply negative EC, rendering any gains practically invisible.
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« Reply #32 on: January 03, 2013, 10:24:22 AM »
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Please reread my post.  This is exactly the type of "proof" I was referring to.  The image taken at ISO 100 had its exposure increased in post to match the image taken at ISO 1600.

In the example I have to offer below, based on the post referred to, it's the opposite. The ISO image was shot "normal" based on an incident meter. The ISO 800 image had to be normalized in post to match as we expect to see with all ETTR images. Otherwise the default rendering appears "over exposed" (but of course, it's not).

http://digitaldog.net/files/100vs800iso.jpg

ISO 800 on this Canon has far less noise than 100. Due to ETTR as Guillermo Luijk first illustrated.
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« Reply #33 on: January 03, 2013, 10:35:57 AM »
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I was under the impression that there were two benefits to ETTR.
1) as you say increase signal to noise ratio.
2) Place the signal you have into the right half of the histogram where you have more exposure gradations, ie higher sampling rate. 

In the case of #1, there is no benefit to increasing ISO as the OP mentions.  In these case of #2, there is a small benefit because after normalization of the tone curve, it may reduce the effect of posterization.

Actually that case #2 has also been debunked by our in-house science professor, Dr. Emil Martin and his work on image noise.  Also, the levels reasoning forgets that image values are not taken directly from RAW values.  A RAW value must be demosaiced, during which time a dozen or more other RAW values will influence the final result of the one pixel's RAW conversion.  Bottom line is that the "levels" limitation only really exists for the least significant bits, which render to near black anyways.
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richarddd
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« Reply #34 on: January 03, 2013, 10:52:13 AM »
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If you decrease ISO, then you can increase exposure with a slower shutter or wider aperture.  If you have a shutter and aperture limit, then you can't really perform ETTR, as the goal of ETTR is to maximizing your signal.  Sure, you can increase your ISO to push the histogram to the right...but your exposure will always be less than optimal.
Higher ISO amplifies the signal. Whether it does a good job is an empirical question.

As to whether you get any benefit from pushing the histogram to the far right via ISO, as I said I believe there is no benefit.  The reason is that the process of applying negative EC to correct the exposure will likely wipe out any gains in reduced noise.  Those gains are in the least significant bits of data, and those are the bits that get dropped when you apply negative EC, rendering any gains practically invisible.
The Canon shot I posted shows a clear benefit from shooting with a higher ISO, even though exposure (i.e., light on the sensor) was unchanged.

We won't necessarily be reducing brightness in post, although it's a distinct possibility.  Exposure is a given and ISO is set so that important highlights are just below clipping, but not beyond 1600. This does not necessarily mean a shot that is too bright.
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bjanes
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« Reply #35 on: January 03, 2013, 10:55:24 AM »
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Thank you! I am a big fan of KISS approach, but for a sake of better understanding please allow me few more questions.

It is my understanding (please correct me if I am wrong) that blinkies, just like histogram, depend not on data in RAW but on data in JPG preview that gets saved with RAW, and in turn JPG preview depends on settings for Picture Mode, Saturation, Contrast and Gradation. Thus am I correct in understanding that one would want them set to something like Muted, toned down Saturation and Contrast, and Normal Gradation while deciding what optimal RAW exposure is? If yes would ETTR at such settings introduce bigger chance of later blowing highlights in the post-processing? I am asking because I think I have seen a shot taken with ETTR and Muted that was not blown yet became blown once one applied iEnhance in post to it's RAW.

You are correct. The histogram and blinkies are from the JPEG preview and not from the raw file itself. Most cameras allow some headroom for highlights by using an ISO sensitivity somewhat higher than the Ssat value measured by DXO, resulting in underexposure. So that the LCD preview and histogram data do not show underexposure, they are adjusted to the right which effectively masks the degree of underexposure. The KISS approach yields satisfactory but not optimal results and one must know one's camera to get better results.

I don't have the Olympus model under discussion, so I will show results for the Nikon D800e. The principles are the same for any camera, but the results will vary. The first step is to expose a uniformly illuminated 18% gray card according to the camera meter (the same results can be obtained by exposing a white target or the computer screen filled with white). I used my computer screen calibrated to a WB of 6500K. The spike in the histogram is somewhat to the right of the expected mid value because of the tone curve applied by the camera (the Nikon standard picture control in this case). The Adobe RGB pixel value was 156 rather than the 117 that would be expected with midgray.



The next step is to look at the raw file. Rawdigger is excellent for this purpose. The gray value for the green channels is 3 EV short of clipping, whereas 18% gray should be 2.47 EV from clipping. This allows for 0.5 EV of highlight headroom. The raw pixel value in the 14 bit raw file for the green is 1986 to give a saturation of 12.1%. In the gamma 2.2 Adobe RGB this corresponds to an 8 bit pixel value of 98.



To get an ETTR exposure, one would have to add 3 EV, and this does show the green channels just short of clipping.



The next step is to look at the camera histograms and blinking highlights for these exposures. As shown in the table below, the plus 2.33 EV exposure gives no clipping in the camera histogram and blinking highlights, and the plus 2.67 EV exposure does show clipping in the histogram and blinking highlights. Backing off of the plus 2.67 EV exposure to the Plus 2.33 one as suggested would give a raw file 0.67 EV short of full ETTR. The camera histogram for the Plus 2.33 EV exposure is shown (one should use the RGB histogram in case there is clipping in the color channels). The ACR results rendered into Adobe RGB are also shown for those who judge ETTR exposure with ACR/LR. For the most accurate results one should use PV2010 with -0.35 EV exposure to compensate for the baseline offset ACR uses for this camera.





Bill




« Last Edit: January 03, 2013, 11:20:25 AM by bjanes » Logged
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« Reply #36 on: January 03, 2013, 11:02:45 AM »
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In the example I have to offer below, based on the post referred to, it's the opposite. The ISO image was shot "normal" based on an incident meter. The ISO 800 image had to be normalized in post to match as we expect to see with all ETTR images. Otherwise the default rendering appears "over exposed" (but of course, it's not).

http://digitaldog.net/files/100vs800iso.jpg

ISO 800 on this Canon has far less noise than 100. Due to ETTR as Guillermo Luijk first illustrated.

Thanks for the example.  Can you clarify your statement...I think you might have left out an ISO value when you said, "The ISO image was shot 'normal'..."  I think you meant, "the ISO 100 image was shot 'normal'..." but don't want to put words in your mouth.  Presuming this is the case...

I see that the bright area of the ISO 100 image has RGB values of just over 200.  On my Nikon D90 I know that such levels would just begin to clip if overexposed by one EV (the Nikon D800 has similar exposure characteristics.)  I'm surprised you were able to amplify that image by 3 stops without any clipping.  That 5D MII must provide a tremendous amount of headroom.

Do you know of the 5D MIII produces a similar result?
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Vladimirovich
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« Reply #37 on: January 03, 2013, 11:10:09 AM »
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The reason is that the process of applying negative EC to correct the exposure will likely wipe out any gains in reduced noise.  Those gains are in the least significant bits of data, and those are the bits that get dropped when you apply negative EC, rendering any gains practically invisible.

we shall assume that you tested all raw converters  Cool ?
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Vladimirovich
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« Reply #38 on: January 03, 2013, 11:16:37 AM »
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The next step is to look at the raw file. Rawdigger is excellent for this purpose. The gray value for the green channels is 3 EV short of clipping, whereas 18% gray should be 2.47 EV from clipping. This allows for 0.5 EV of highlight headroom.
camera metering (spot metering or matrix/centerw off a uniform surface) does not care what is your target actual reflectance... it is assuming some (manufacturer defined) reflectance regardless whether you meter off true 18% grey card or white snow and in most cases it is 12.x% (some camera models do differently)... and head room for different channels will be different for different illumination... so you test for a daylight, but you test for tungsten bulb as well and so on.
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« Reply #39 on: January 03, 2013, 11:17:34 AM »
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The Adobe RGB pixel value was 156 rather than the 117 that would be expected with midgray.

Oy...that drives me crazy.  What I realized is that the picture control has some sort of auto-levels function that increasing the brightness.  I created a custom picture control from the Neutral PC using ViewNX, and that gives me the expected value on the camera.
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