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Author Topic: lower EC or ETTR?  (Read 26038 times)
deejjjaaaa
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« Reply #40 on: August 14, 2012, 12:02:12 PM »
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I'm not sure what I'm supposed to get from that.  After presenting the same unsubstantiated information that everyone else does and making some quesitonable presumptions, it seems like he took a few pictures and then proceeded to draw conclusions that probably should have been experimentally verified with an additional set of captures demonstrating saturation at the predicted overexposure levels.


well to his credentials he is one of two people behind rawdigger and libraw (along w/ Iliah Borg)... and yours ?
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Guillermo Luijk
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« Reply #41 on: August 14, 2012, 12:58:48 PM »
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Quote from: hjulenissen
I must confess that I fail to see why "18%" or "12.7%" would ever have to be mentioned in a discussion about digital cameras. Film cameras might be another story, but I don't know much about those.

I agree.

The gray reference is still important to digital cameras because that's how the camera meter works.

In a modern digital camera (unfortunately this still excludes most DSLR cameras), the camera meter is completely unnecesary and obsolete. In my M4/3 camera (those ones you ridiculize because of their optimized sensor size), I don't need to meter anything to quickly obtain accurate exposure (which can be either ETTR or a perfect JPEG), basically because its electronic viewfinder allows me to use a real time pre-visualization method (you can see how the final image will result before clicking the shutter), versus the old fashioned metering + post-visualization scheme most DLSR's use (that often requires iteration to obtain accurate exposure).

Most camera users don't shoot in a studio with several flash lights, and don't want heavy and bulky gear hanging in our necks. We just take pictures in our trips, countryside and city walks, or friends and family meetings. For us digital capture using the camera meter is a completely obsolete technique. It's just the big camera manufacturers haven't realised yet and even in their entry level cameras still prefer to implement this obscure and rudimentary tool:


rather than providing the user a real time scene's preview where underexposed and clipped areas are displayed in an intuitive way.

Regards
« Last Edit: August 14, 2012, 05:09:45 PM by Guillermo Luijk » Logged

deejjjaaaa
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« Reply #42 on: August 14, 2012, 02:03:14 PM »
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I don't need to meter anything to quickly obtain accurate exposure (which can either be ETTR or a perfect JPEG), basically because its electronic viewfinder allows me to use a real time pre-visualization method (you can see how the final image will result before clicking the shutter), versus the old fashioned metering + post-visualization scheme most DLSR's use (that often requires iteration to obtain accurate exposure).

ever tried tungsten light - how accurate is your meter (w/o you adjusting what camera meters)
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Graystar
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« Reply #43 on: August 14, 2012, 02:43:36 PM »
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well to his credentials he is one of two people behind rawdigger and libraw (along w/ Iliah Borg)... and yours ?

I don't have any.  That's why any information I give can be easily verified by anyone reading.
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deejjjaaaa
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« Reply #44 on: August 14, 2012, 03:06:27 PM »
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I don't have any.  That's why any information I give can be easily verified by anyone reading.

 Wink ... an everybody w/ Canon 5D mkII can verify spot metering himself/herself based on the technique described
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hjulenissen
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« Reply #45 on: August 14, 2012, 03:41:04 PM »
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You seem to be very much concentrated on describing how Auto-Exposure in most current cameras work. That is important knowledge for most of us.

Knowing that no man-made Auto-anything is perfect, I am more interested in how exposure ideally should be set (either using manual labour, or some improved algorithm).

From my point of view, positioning the middle tones at some pre-defined point along the sensor DR without regard for saturation is just backwards for digital sensors. The fact that it has worked for many years for film, and that many digital manufacturers/users are able to make good images using rules of thumb does in no way prove that it is the best way to do things.

An example (mentioned by Graystar?) is a landscape where 1/2 is directly lit, while 1/2 is in the shade, or 1/2 is the evening sky, while 1/2 is landscape below. The photographer might want to capture as much information as possible about the entire scene (perhaps expecting to use a simulated graduated ND filter in Lightroom afterwards). The best way to utilize a limited DR digital sensor would probably be to bring the bright parts as close to the clipping/significantly non-linear part of the sensor as possible. Then the dark parts would be raised as high as possible above the noise-floor, and hopefully acceptable. If the scene DR is too high compared to the sensor DR, no single-image non-ND-filtered shot is going to capture it satisfactory, no matter what exposure technique.

-h
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digitaldog
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« Reply #46 on: August 14, 2012, 03:46:20 PM »
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Before we talk about exposure, exposure meters, what percentage they ‘see’ (which shouldn’t be important), don’t we have to properly define the processing too? We’d never take color neg film, pop the ISO suggested into the meter and then blindly accept that without bracketing quite a bit, then including the processing of the film into the proper exposure system would we?

The meter may tell us one thing. Is it really automatically dialed into the raw processing? Nope. Do we know the limit the sensor can record the highlight data we want to capture (not blown out), without bracketing and testing the raw processor to see at what point we really do clip data versus seeing what appears to be clipped that isn’t until we normalize the rendering using the various sliders? What appears totally blown out using the meter recommendation on the LCD is absolutely no indication the data (raw) really is blown out. I don’t see how we can discuss exposure without introducing development into the process. At least for raw.
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Andrew Rodney
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deejjjaaaa
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« Reply #47 on: August 14, 2012, 05:05:17 PM »
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to bring the bright parts as close to the clipping/significantly non-linear part of the sensor as possible.

but then you need to decide if those bright parts are more important colorwise than noise in shadows - may be you can allow yourself to place bright parts into non linear area and sacrifice there to gain better SNR for shadows (that is when bracketing, graduated filters, etc can't be used)... so it is case by case decision.
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Guillermo Luijk
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« Reply #48 on: August 14, 2012, 05:33:52 PM »
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From my point of view, positioning the middle tones at some pre-defined point along the sensor DR without regard for saturation is just backwards for digital sensors. The fact that it has worked for many years for film, and that many digital manufacturers/users are able to make good images using rules of thumb does in no way prove that it is the best way to do things.

I agree again with you guy Grin
Let's consider the 3 stages in a digital workflow: scene -> capture (RAW file) -> output image (print, digital image,...):

  • The capture can be freely mapped over the output image. What could be tricky in the past, today is a simple input/output curve in Photoshop so the correspondence between capture and output doesn't deserve much discussion.
  • Thanks to sensor linearity, RAW exposure is only important regarding highlight clipping and noise. Colours, contrast,... remain the same no matter what RAW exposure was achieved. What a valid RAW capture is (e.g. ETTR) has been widely discussed so I think again it doesn't deserve more discussion.
  • What it's new and interesting IMO is the correspondence between scene and output image. Camera metering/Zone System exposure based criteria said a 18% gray card should end in the middle point of the perceptual luminance scale. Does it make sense? or this was just an arbitrary rule that worked in the past but can be ignored? should every particular reflectivity in real life end at the same luminance point in the output? should a picture of a Kodak graycard be L*=50% in the output no matter if the picture was taken at 12h00 in a sunny day or at 21h00 with the sun set and the sky darkening?

Regards
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hjulenissen
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« Reply #49 on: August 15, 2012, 12:43:25 AM »
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but then you need to decide if those bright parts are more important colorwise than noise in shadows - may be you can allow yourself to place bright parts into non linear area and sacrifice there to gain better SNR for shadows (that is when bracketing, graduated filters, etc can't be used)... so it is case by case decision.
Yes, if the scene DR is larger than the sensor effective DR, you might have to compromise both the top end and the bottom end (if you want to do it in one shot, no graduated ND etc). There are two ways of seeing this:
1. You are off into subjective land, and only trial & error, experience and good old luck will guide you
2. You may be able to sacrifice highlights, either because you don't care about them, or because you believe that they can be salavaged. This sacrifice may or may not be sufficient that you can "ETTR" the next-brightest parts.

-h
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hjulenissen
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« Reply #50 on: August 15, 2012, 12:49:40 AM »
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What appears totally blown out using the meter recommendation on the LCD is absolutely no indication the data (raw) really is blown out.
I don't think that there is _no_ correlation between those two. The problem is that the correlation is far from perfect?

Yes, camera manufacturers do their best to make this hard. Amazing, really. Up until they get their act together, I think that a lot of confusion can be avoided by trying to figure out how exposure ideally should be (on digital cameras). Many people seem to have wildly different ideas of how exposure should be, perhaps based on experiences with film, with complex raw developers, or with misleading intuition. We all have to accept compromises, and 1 or 2 stops of metering uncertainty headroom may be one of those - for now.

-h
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hjulenissen
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« Reply #51 on: August 15, 2012, 01:05:25 AM »
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  • What it's new and interesting IMO is the correspondence between scene and output image. Camera metering/Zone System exposure based criteria said a 18% gray card should end in the middle point of the perceptual luminance scale. Does it make sense? or this was just an arbitrary rule that worked in the past but can be ignored? should every particular reflectivity in real life end at the same luminance point in the output? should a picture of a Kodak graycard be L*=50% in the output no matter if the picture was taken at 12h00 in a sunny day or at 21h00 with the sun set and the sky darkening?
Pure guesswork:
Film had a more _symmetric_ error behaviour than digital. The brightest parts and the darkest parts of the scene were somewhat gradually distorted. Due to this, it made sense to center the histogram close to the mid-point (assumed most linear). For high DR scenes, you either used wide DR film, or the highlights would be compressed and the shadows would be noisy, and that was ok.

If I am right, the "18% gray" rule really is more about capture exposure than end-to-end exposure. Only because the two were practically interlocked did they not separate.

It would be interesting to know what those who shoot film today (with its response curves), but using a digital postprocessing approach (with the freedom to manipulate exposure and tonality afterwards) do with their field exposure?

Capture exposure and rendering exposure can never be perfectly separated (even though we would like it):
If you know that you want to do a (extreme) high-key or low-key image, you might only be interested in a small portion of the histogram. Then ETTR digital or 18% film may not be the best option simply because most of the captured information is going to be clipped in print anyways, and the (histogram tail) information that you do care about might not be captured optimally. So ETTR and similar should not be stated "push the brightest parts of the scene as far to the right as possible without entering sensor nonlinearity". It should be stated "push the brightest parts of the scene that you care about as far to the right as possible without entering sensor nonlinearity"

-h
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Graystar
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« Reply #52 on: August 15, 2012, 06:38:55 AM »
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Wink ... an everybody w/ Canon 5D mkII can verify spot metering himself/herself based on the technique described

That's right.  But even if verified as correct (because at this point they haven't been, as far as I know,) the results only matter to ETTR practitioners.  And even then, no metering methodology was described.

I don't have a 5DMII, but unless its meter calibration is vastly different than other Canons like the 7D, I can tell you that if you spot meter a neutral, evenly lit surface, then a white-balanced RAW conversion of the resulting capture, with no additional processing, will have sRGB values of 100, 100, 100 at the metered area.  That's 12.7% gray.  The reason that's important is because it tells you exactly how much headroom you have above the metering point...which is just under 3 stops.

The article stated that the metering point gave 3.6-3.8 stops (or thereabouts) of headroom.  But what about tungsten light (as you've mentioned) or worse, sodium lights?  That headroom is gone in those instances.  I don't practice ETTR and even I have to cut back my exposure by 1/3rd stop in those conditions.

The camera makers cannot base their metering systems on ETTR practitioners.  The metering is (currently) designed to match film-based metering.  And when metering as such, the processing has to allow for no clipping of reflected white under a very large range of lighting conditions.  And if that requirement resulted in some unused headroom in daylight conditions, then so be it.  ETTR practitioners can make use of the headroom when it's available, or just overexpose to their liking...whatever.  But don't invalidate other's metering methods just because they don't fit with YOUR view of how digital should be metered.

I have an RMI Digital Gray Card that I use for both white balance and for setting exposure when in constant-light conditions.  The reference itself is marketed as a WB tool only, as it's about 30% gray.  But I determined an appropriate EC value by shooting some 92% bright copy paper under a 5000K light until RawDigger indicated saturation, then just placing the reference in the spot-meter area to see the difference in metering.  That's my EC, which turned out to be about 1.3 EV (1.0 EV when the light gets red.)

Anytime I step into new light I will pull the gray card from my back pocket, perform a custom white balance, and if the light is constant, I'll just press my AE-L button to lock exposure.  That's it...I'm done with exposure.  I can photograph anything illuminated by the same light and know that I won't clip any reflected highlights.  Could I have pushed exposure by 1/3 or 2/3 stops in some cases?  Sure...but I rarely shoot scenes that are so static that I have time to figure that out, and I usually don't care about having 2/3 stop more noise.  The only time it matter to me is when photographing my black dog.  In that case I'll just use the ETTR that's built-into my camera...the expanded ISO range.  I'll just set my Nikon to L1.0...instant ETTR.
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digitaldog
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« Reply #53 on: August 15, 2012, 09:17:09 AM »
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I can tell you that if you spot meter a neutral, evenly lit surface, then a white-balanced RAW conversion of the resulting capture, with no additional processing, will have sRGB values of 100, 100, 100 at the metered area. 

What raw converter with what (default) settings?
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Andrew Rodney
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Graystar
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« Reply #54 on: August 15, 2012, 10:07:42 AM »
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What raw converter with what (default) settings?
LightRoom with its neutral profile...I forget the name of it, but it doesn't apply any processing.

Raw Therapee with the "Neutral" profile.

Rawnalyze with sRGB.
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digitaldog
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« Reply #55 on: August 15, 2012, 11:01:36 AM »
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LightRoom with its neutral profile...I forget the name of it, but it doesn't apply any processing.

Neutral Camera profile? Neutral (default) rendering settings? Who says either are ideal? They are just a starting point. I can set the camera to ‘over expose’ 1.5 stops past what the meter recommends, normalize the image in LR using Exposure. So what makes my capture and your capture different, which is ideal?

Again, I don’t see how we can separate the exposure from the processing. Setting a 1.5 stop increase will blow out the JPEG but the raw is just fine after normalizing in my raw converter.
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Andrew Rodney
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deejjjaaaa
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« Reply #56 on: August 15, 2012, 11:22:26 AM »
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But what about tungsten light (as you've mentioned)
metering will underexpose...
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Graystar
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« Reply #57 on: August 15, 2012, 11:38:37 AM »
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Neutral Camera profile? Neutral (default) rendering settings? Who says either are ideal?
Not me.  My words on the subject, located elsewhere in the thread, is that standard exposure is a tool, not a destination.

Quote
They are just a starting point.
Exactly.  Darn good starting point.

Quote
I can set the camera to ‘over expose’ 1.5 stops past what the meter recommends, normalize the image in LR using Exposure. So what makes my capture and your capture different, which is ideal?
As I said, standard exposure is just a tool.  It allows me to know what I'm getting.  What I get may be just right, or may require an hour or more of processing.  What's important is that I know I've captured a good starting point.

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Again, I don’t see how we can separate the exposure from the processing. Setting a 1.5 stop increase will blow out the JPEG but the raw is just fine after normalizing in my raw converter.
1.5 stop increase over what metering point?  And to what JPEG are you referring to...an OOC or one with no processing?  I'm trying to ascertain whether the blown highlights are from the initial RAW conversion, or from one-size-fits-all default processing.  I'm no fan of OOC JPEGs, but I find that when using the Neutral picture control of my Nikon, that OOC JPEGs won't clip white unless RAW does (red is always another story.)
 
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digitaldog
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« Reply #58 on: August 15, 2012, 11:43:02 AM »
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1.5 stop increase over what metering point?  And to what JPEG are you referring to...an OOC or one with no processing?

Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.

The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.
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Andrew Rodney
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Graystar
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« Reply #59 on: August 15, 2012, 12:19:50 PM »
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metering will underexpose...
When metering under tungsten light, if I increase exposure by 1/3rd stop over standard exposure, I will clip the green in bright white objects.  So my Nikon, at least, doesn't underexpose in tungsten light.
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