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ETTR metering mode

Discussion in 'Open Discussion' started by dhazeghi, Jun 10, 2012.

  1. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    One of the most useful innovations of mirrorless systems like m4/3 is the Live Histogram, which allows one to essentially prejudge exposure.

    It seems to me that an obvious extension would be to have a metering mode that uses the histogram the same way we often do, setting the exposure to be as high as possible without clipping highlights too heavily (or at all) - in essence an expose-to-the-right (ETTR) metering mode. Unfortunately, while they've been able to all sort of other clever things (e.g. face detect AF), metering seems sadly to still be stuck in the stone ages - we've got spot, center, and matrix mode (ESP on Olympus), and even matrix mode is still biased to the illusive and fictional 'middle gray'.

    Does anybody else think an ETTR metering mode would be useful? Or have any suggestions how to achieve such results today without having to babysit the exposure constantly?

    Thanks,

    DH
     
  2. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    Using the exposure compensation wheel you can shift the meter's target to control ETTR.

    What you can't do is change the shape of the histogram, unless you use Gradation (essentially a post-processing curves adjustment) or do something external to the light distribution in the scene itself.
     
  3. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    I don't quite follow. Obviously using EC changes the exposure (per the name) but how does it affect the metering?

    The shape is fine. All I want to do is have it shifted so the right tail is always at or very near the right edge of the histogram.

    Thanks,

    DH
     
  4. b_rubenstein

    b_rubenstein Mu-43 All-Pro

    Mar 20, 2012
    Melbourne, FL
    I've read this before in a piece on Luminous Landscape and the author didn't have a particularly good grasp of the underlying concepts digital signal processing. Exposing to the right, only, and I do mean only, improves the S/N (Signal to Noise Ratio).

    Since low noise has become such a huge metric for camera buyers, camera makes have been tweaking the metering for hotter exposures. When I bought my D200, the matrix metering tended to meter to preserve highlight details, which is critical for pictures of people. (Clip the red channel for a Caucasian skin tone and there is no post processing that will render a smooth transition from shadow to highlight.) All my more recent cameras tend to hot exposures for low noise rather than preserve highlights. This is why camera makes have included processing/exposure tweaks like Nikon's Active D-Lighting (which even effects RAW files just like Olympus' AUTO Gradation setting).
     
  5. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    And less noise = more detail. I would say the major improvement of large sensors over small sensors and newer cameras over older ones is precisely in that regard - more and better detail.

    Auto gradation is actually quite primitive - it drops exposure by 0.3EV and then boosts the shadows in JPEG processing. I believe ADL does somewhat more.

    But my point goes beyond just ETTR. The meter today has access to a wealth of information from the sensor - and almost all of it seems to be ignored.

    Though I don't think ETTR, implemented as I suggested, would cause you any particular problems. Simply set the highlights clipping area limit to 0% on the red channel.

    DH

    P.S. When postprocessing files from the E-PM1 shot with standard metering on a nice day, the first thing I have to do is increase the exposure on 75-80% of the files, so that clouds and foam are white (not gray). A 0.5 or 1EV push invariably means that the midtones are full of noise (and after NR, lacking fine detail).
     
  6. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    All I meant about the exposure compensation is that you're telling the camera the neutral grey that the sensor is "seeing" is to be shifted from it's centered position, by over/under exposing. This effectively drags the histogram along with it.

    The more you try to work the data off the sensor the more high speed processing you need to get through the calculations in small fractions of a second. The latest in camera multi-processors help, but it also needs high chip frequencies, and those are a real battery drain as well as producing too much heat for natural cooling to be sufficient.

    I have noticed that some of my lenses seem to produce histograms that are a lot more evenly distributed for a given lighting situation, while others are quite narrow in their captures. In the old days we would have talked about the difference being that one lens was more contrasty than the other.
     
  7. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    Really? My impression was that the metering occurred independently, and then the EC was simply applied linearly after the fact.

    I don't think there's that much additional work involved. I mean, they're already rendering the image, with distortion correction, and computing the histogram on the fly. The exposure data can be computed directly from the histogram as it's being generated.

    True. And I'll bet it's mainly the older lenses produce a much broader histogram on the cameras, thanks to that lower contrast (or occasionally, haze on the lens).

    DH
     
  8. stratokaster

    stratokaster Mu-43 All-Pro

    Jan 4, 2011
    Kyiv, Ukraine
    Pavel
    DH, your Olympus has a very useful metering mode called Spot-Highlight. Just take a reading off your clouds and they will be exposed as highlights (i. e. they will be white, not gray).

    I actually have one of CUSTOM modes on my GH2 permanently set to spot metering and +2 exposure compensation as an attempt to recreate this Spot-Highlight feature.

    - Pavel
     
  9. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    It seems to me that you don't know what you're asking.

    First, you can use the histogram display to show whether or not you've got any clipping, and the highlight/shadow display to show you where that clipping is, but there's no way for the camera to know whether or not any clipping is in an area that's important to you. The camera can't tell whether the clipping is because you've got a light source in the frame that's going to clip pretty much regardless of how you expose, or whether the clipping is a highlight on the face of a person in an area in shadow and that you want to maintain detail in that highlight. The meter can measure the light and give you info about what the dynamic range of the light in the scene is like, and the highlights/shadow display can show you where the clipping is occurring, but neither is capable of deciding whether or not clipping is a problem for you with that shot. That has to be your decision.

    Second, you say all the modes are "biased to the illusive and fictional 'middle tray'". What do you want them to be based on? Middle grey isn't fictional or illusive. For a start it is rather precisely defined and it is the luminance value for scenes with an average range of lighting levels distributed evenly within the frame. It works for "normal" shots and gives a reasonable result. What would you have meters set to? You need to have them calibrated to some reference level. What level would you propose and why do you think that level would work better than middle grey?

    Every light meter made, whether it be in a camera or separate, is calibrated to middle grey which became the accepted standard for good reason. No camera manufacturer is going to change from an accepted international standard without very compelling reasons so, if you think that there should be a change, what are your reasons and what do you think the standard should be changed to?

    With an Olympus (at least with my E-P3), in menu D of the cogs menu there's an option called "Live View Boost". If you set that to "Off", the display will respond to changes in exposure compensation, showing how things in the frame will lighten or darken as you adjust exposure using the exposure compensation dial. Using the histogram display you also get to see the histogram move to the left or right depending on what compensation you're setting, and the highlights/shadow display is active also showing you how any areas of clipped highlights or shadows are increasing or decreasing as you adjust the compensation. You can shift the exposure to the right or left and see just what effect that will have in your photo as you're doing it. What more do you want? I've got a friend with a Nikon DSLR who would love to have that option.

    My E-P3 actually gives me 3 spot metering modes, not one. A "standard" mode based on middle grey, a highlight mode and a shadow mode. I've tried working out what the differences in values between those 2 modes and the standard mode is and they seem to be set at + or - 2 to 3 stops from the standard, middle grey value. If I meter a shadow area using the shadow mode, the exposure produces a result that makes the area metered dark enough so that details aren't visible, basically zone 2 if you want to use the zone system. The highlight mode puts the metered area as light, also without visible detail, the equivalent of zone 8. I don't find the shadow mode useful but what you can do with the other modes is the following:

    - using normal spot mode, set exposure compensation to +1 and meter caucasian faces and you will get the right skin tone. Set exposure compensation to -1 for dark skinned faces such as Australian aboriginals or african americans and you'll get that skin tone pretty right. Basically that's setting your camera to expose based on light or dark skin tones.

    - using the highlight spot mode, set exposure compensation to -1 and meter the brightest area in the scene in which you want to retain detail. That will give you highlights with detail which is what you want if you're going to use ETTR. Just make sure you don't measure highlights like the sun or an exposed light or you'll end up with everything else underexposed which isn't what you want.

    Even if you're using the ESP or centre weighted modes on an Olympus, if you set Live View Boost to "Off", you can watch the effects of changes in exposure compensation as you make them and simply "dial it in" until the viewfinder is showing things looking the way you want them to look in your finished shot.

    The metering modes and exposure information available in the display of my E-P3 seems to me to offer pretty much everything anyone would want, provided they're prepared to spend a bit of time learning how to use the options available and taking a few test shots to see just how what they're seeing in the viewfinder matches up to the results they get when they process their photos.

    You just have to learn to use what's there, and there's a hell of a lot more there in metering flexibility than you think.
     
  10. crsnydertx

    crsnydertx Mu-43 Top Veteran

    995
    Dec 31, 2010
    Houston, TX
    Chuck
    Pavel, thank you for that tip. That function is available even in the lowly E- PM1; will have to test it. Converse setting (spot metering/shadow control) is also an option. Every day I learn of another gold nugget buried in those menus...!
     
  11. crsnydertx

    crsnydertx Mu-43 Top Veteran

    995
    Dec 31, 2010
    Houston, TX
    Chuck
    David, re your use of -1 EC with spot-highlight mode: is that to prevent driving the spot all the way to white?
     
  12. stratokaster

    stratokaster Mu-43 All-Pro

    Jan 4, 2011
    Kyiv, Ukraine
    Pavel
    I'm glad you find this bit of information useful. Actually this feature (shadow/highlight spot meter) is available on nearly all 'serious' Olympus cameras starting with the OM-4.

    P. S. I'm Pavel, not Patel ;)
     
  13. crsnydertx

    crsnydertx Mu-43 Top Veteran

    995
    Dec 31, 2010
    Houston, TX
    Chuck
    Apple chose to disagree; iPad spell check strikes again! I corrected it before I got your note, but you're too quick for me. My humble apologies...
     
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  14. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Yes. You can have more than one highlight that you're prepared to see go white and they may very well not have the same luminance values. if, for example, you've got 2 different highlight areas that you're happy to see go white and they happen to be 1 stop apart in brightness, metering the brightest one will result in the non-highlight areas of the frame being 1 stop underexposed compared to the result you will get if you meter the other highlight.

    Metering for the brightest area you want detail in makes sense. You don't want to lose detail that you want to keep, and this approach ensures that you preserve that detail while placing it as far to the right as you can put it if you want to adopt ETTR as a general shooting strategy. Basing your metering on an area that you're happy to see go white may give you a result that has the area you want detail in going white also if they're too close in value.

    What I'd do if you want to try this approach is to take some test shots metering a highlight area in which you want to preserve detail. Try some using the straight highlight spot mode and some with -1 exposure compensation. See which result you prefer. I suspect there's a certain tolerance in meter accuracy from camera to camera, and what I call "preserving detail" may not be quite the same as what you call that. Try it both ways in a number of situations and see which one consistently guarantees the results you want with your camera and exposure tastes. I would suggest not metering the areas you want to go to white simply because there may not be enough difference between them and the highlight areas you want to retain detail in to guarantee you retain that detail. After all, the spot zone on the sensor can actually be bigger than the highlight area you're measuring in many cases so you may not get a "pure" highlight reading and the more non-highlight areas there are in the spot zone, the more likely it is that the reading you get is going to ensure areas slightly lower in value in which you want to retain detail are also going to go white.
     
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  15. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Two additional points to my earlier posts:

    First, an additional feature in Olympus bodies:

    In menu J of the Cogs menu there's a feature called "Exposure Shift". It enables you to set an automatic shift of up to +/- 1 stop, in steps of 1/6 stop, for the ESP, Centre Weighted and Spot modes. For dhazeghi this is the equivalent of resetting his meter to something other than middle grey. Basically it allows you to set a permanent amount of exposure compensation and to do so separately for each of those metering modes. Unfortunately it doesn't allow you to set a different value for each of the 3 spot modes and I assume whatever value you set for spot will apply to all 3 spot modes.

    Second, I said in my first response that I didn't find the shadow spot mode particularly useful. There is one situation in which I do think it is useful. That is if you want to photograph something as a silhouette. Set the meter to shadow spot meter mode, meter the person/object you want to have as a silhouette, and shoot. Whatever you meter will go to dark with at most just a little detail showing. If it doesn't end up dark enough for you and/or the highlight area behind it isn't bright enough in comparison, a boost in contrast should give you the result you want.
     
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  16. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    For dhazeghi:

    You asked for an ETTR mode.

    With Olympus bodies, the highlight spot mode will do that provided you meter the brightest highlight area in which you want to retain detail and dial in enough exposure compensation to ensure that you retain the detail to your satisfaction. A few test shots will help you work that out.

    You won't get an ETTR mode without using spot metering. The ESP and centre weighted modes both measure too much of the scene so there will be a lot of variability between the reading they give and the luminance of the brightest highlight area in which you want to retain detail. That variability arises because not all scenes have the same contrast and there will be a greater difference in exposure value between the exposure you need to preserve highlight detail and the meter reading in both of those modes if your scene has a high dynamic range than if it has a normal dynamic range, and an even greater difference if the scene has a low dynamic range. You can't measure a large part of the frame, or the total frame, and expect to be able to make a standard adjustment to the recommended exposure in order to get the highlights where you want in value. If you want to ensure that the highlights get consistently treated in a specific way you need to measure the highlights themselves and that means using a spot meter mode.

    With the highlight spot mode you've got the metering mode you want, provided you measure the right part of the scene. All you have to do is work out just how much negative exposure compensation will guarantee that you always retain detail in those highlights in which you want to retain detail, make sure to measure those highlights, and you will get your histogram pushed as far to the right as is it is safe to push it.

    If you don't want to use a spot mode, then regardless of whether you want to use ESP or centre weighted mode, ensure that you've got Live View Boost turned off so you can see the effects of exposure compensation in the display as you adjust it. Then, using either the histogram or highlight/shadows option, start adjusting exposure compensation watching the histogram or highlight/shadow display and adjust until you get the display where you want.

    Regardless of how you meter I would still recommend looking at how the scene displays in the viewfinder/on the screen, especially if your scene has a high dynamic range. If it does have a high dynamic range you may find that preserving detail in highlights results in lower value areas which are more important ending up underexposed and you may have to make a choice between exposing for those areas and losing more highlight detail than you want, or keeping the highlight detail and working with underexposure in some of your important areas. Looking at the actual scene display with the highlight/shadow indication on will help you make that choice. You definitely won't be able to make it with reliable consistence using the histogram because while the histogram will show you how many pixels are blowing out, it won't tell you which pixels they are and what their effect on your image will be. The highlight/shadow display gives you that. I find the histogram display becomes increasingly less useful to me as the number of blown pixels increase, and the highlight/shadow display becomes increasingly more useful to me as that occurs.

    Unfortunately each sensor has a fixed and limited dynamic range and sooner or later you'll get scenes which put you in the position of having to make that choice. The E-M5 has a wider dynamic range than the PENs and you won't have to make that choice as often with it as you will with a PEN but sooner or later you will still have to make it. Until someone makes a sensor with a much greater dynamic range than any camera currently available, that is going to remain the case. If there's 3 to 4 stops difference between the mid tones and the highlights where you want to keep detail in the scene you're shooting, you should be able to accommodate that with either a PEN or an E-M5 but you will have to play with the files from the PEN a bit more. If the range is, say, 6 stops or more then you're going to be making a choice between mid tones or highlights with the current range of m43 bodies, simply because they don't accommodate overall dynamic ranges of 12-13 stops or more. As always shooting RAW will give you a wider dynamic range and I've based my estimates here on shooting RAW. You'll have less scope for accommodating a wide dynamic range if you choose to shoot JPEG.
     
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  17. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    I've always kept live view boost turned off so I can see what I'm really capturing as I shoot. Sometime last year (on Ned's advice) I set up both my cameras (E-PL1 and E-PL2) with back button focus and spot metering. It's really liberated me from the camera being in control of my exposures without making me constantly change settings to get what I want. Now that I can set the scene metering separately from the focus I just point the camera at anything of the right brightness to capture the image the way I want it to look in the viewfinder, lock the exposure, recompose, finalize the focus, and shoot.

    The display aids like the histogram, or the over/under red/blue highlights just add to the ability to know what kind of light distribution I'm getting as I shoot. It's made it really quick and easy to take several shots in a row with subtle differences just by moving the spot metering target slightly for each one. It's somewhat like the film days of working with the zone exposure system but much more intuitive and immediate.
     
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  18. b_rubenstein

    b_rubenstein Mu-43 All-Pro

    Mar 20, 2012
    Melbourne, FL
    The fundamental metering issue is that the metering system doesn't know what's in the scene. Even Nikon's Matrix metering is nothing more than a look up table based on statistical analysis of images. Until the metering system can reliably differentiate between something like a specular highlight and a light spot on someone's forehead, the photographer will remain a key element in setting exposure.

    I would still rather deal with a little added noise than lost, clipped data. Noise reduction is the type of signal processing that lends itself to post processing because it doesn't have to be done all that quickly and current PCs have significant processing power.
     
  19. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    Hi David,

    first, thank you for your incredibly detailed response. You raise many interesting points, and I will try and put some of them into action.

    I do want to clarify one point - I don't expect the camera's metering provide optimal settings 100% of the time. Rather, I'm looking for a better baseline. My primary gripe is that the camera is already processing a great deal of data in real time, and I believe at least some of this could be incorporated to get better metering. Algorithmically, it is fairly trivial for the camera to determine the maximum exposure that does not blow more than 1% of the pixel values, and as far as I can tell this would provide a better starting point for me than the current options. I suspect it would be useful to others too, but perhaps I'm wrong there!

    You're right that middle gray does have its uses (I was being a bit dramatic in my comments), and I see nothing wrong in maintaining traditional metering modes as well. Still, it does seem a fairly primitive way to go about things considering how much more data the camera has at its disposal compared to 20 or 30 years ago.

    Regarding Live View Boost, I haven't had too much luck judging exposure based on the EVF with it enabled, but the histogram seems to serve the purpose there, so I've not experimented as much.

    I will have to give more attention to the spot metering modes.

    Thanks again,

    DH

     
  20. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    What you are suggesting would have to be set ahead of time by the user. 1% pixels? Why not 5%? Why not .5%? What you are suggesting is have the camera guess at what is suitable for blown out highlights.

    In my everyday uses, ETTR has yet to prove beneficial for any significant amount of my shooting because the DR I normally shoot is greater than than the sensor provides(E-PL2). New technologies in the E-M5 show that shadows can be pushed without being too noisy.

    If I am ETTR, sometimes I need the most contrast in the highlights, which means the shadows are still dark. Other times I don't mind blowing out the highlights or even more than just the highlights to properly expose the shadows.

    If a scene's DR fits into what the sensor can do, having the camera ETTR by default might make some sense. But if it doesn't, the choice has to be left up to the shooter to figure out what is important to blow out or underexpose.