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Correct exposure?

Discussion in 'Open Discussion' started by Hyubie, Jun 22, 2011.

  1. Hyubie

    Hyubie Unique like everyone else

    Oct 15, 2010
    How do you know if an image is over- or under-exposed? Not talking about prior to taking the shot, but when you are looking at the image on your computer (JPG or RAW).

    (Please let's not argue why the exposure was incorrect in the first place prior to taking the shot, or even the JP*G/R*W discussion. Let's just take them as a given for this question. A few recent threads veer away from the original post when something arguable like this is brought up. :wink:)

    I usually see that it is a bit dark or a bit blown here and there, but only from time to time. When reading some photography articles online, people say something like the camera tends "to be a tad over-exposed, so I'd set the camera to -0.03 EV". How do they know how much that "tad" is? When I try that amount of adjustment on an image, the difference is not too discernible to me.

    So - is it purely based on your trained eye, or is there a tool somewhere like in Lightroom, or Photoshop, or other software that tells you an image is not properly exposed?
  2. starlabs

    starlabs Mu-43 Top Veteran

    Sep 30, 2010
    Los Angeles
    Turn on the in-camera histogram display.

    It's my understanding that if the majority of the graph is too much to the left or right edges, your picture is in danger of being under or over-exposed.

    My bad, you meant after the picture has been taken. Well, you can look at the histogram then too...
    • Like Like x 1
  3. Luke

    Luke Mu-43 Hall of Famer

    Jul 30, 2010
    Milwaukee, WI
    The answer I prefer is that there is NO correct exposure. But starlabs has hit the nail on the head. The camera (and any proper photo editing programs) have histograms to show you a graphic representation of your exposure.

    It's correct when you've adjusted it to the point where you the shot looks like you see it in your head.
    • Like Like x 1
  4. Djarum

    Djarum Super Moderator Subscribing Member

    Dec 15, 2009
    Huntsville, AL, USA
    I think correct exposure always boils down to personal view. Histograms are a good way to evaluate the entire scene.

    However, correct exposure becomes a little more problematic when there is a ton of contrast in the scene. A histogram could show correct exposure for the entire scene, but the subject of the image could be either underexposed or overexposed. When these sorts of problems arise with exposure in a scene, it is always a judgement call for the photographer to deal with the balance between the exposure of the entire scene and that of the subject.
    • Like Like x 1
  5. Pan Korop

    Pan Korop Mu-43 Veteran

    Mar 31, 2011
    Phare Ouest
    Correct exposure is no loss of information where information was relevant. In practice:
    -- burnt sky, highlights, with that typical digital colour fringe around = overexposed
    -- sooty, noisy shadows, when one would like to see details in there, like in Rembrandt light = underexposure.
    -- the medium values in-between may appear too dark or light, no big deal: you'll tweak it by the gamma curve in post-processing. Main goal is to get the low and high values unsooty/unburnt.

    This is why the histograms are handy: if their "mountain" is clipped to the left, shadows are too dark (and vice-versa on the right). Now if there is a flat space between the left of the histogram frame and the beginning of the uphill, you're probably overexposing.

    This is an ideal world, with cameras having perfect dynamic range... In the real world contrasty scenes--sunlight or worse, backlight--something will get clipped to the left or the right, or both. There it's you who has to decide where the loss of info is acceptable, where not--highlights or shadows.

    At first, when in doubt, bracket! You'll be able to choose the "best" option afterwards. Or resolve to combine the extremes in a HDR combo, i.e. the no-choice solution between the high and low values, at the expense of medium values punchiness. A "safe" solution... which sometimes is dangerous, for lacking the guts of choice. But this would need another thread :) 
    • Like Like x 2
  6. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Trained eye. Software can't tell you if an image is properly exposed, because software doesn't know if your image is high-key or low-key, or what your subject is that should be exposed to, etc.

    Yes, there are histograms and they can tell you if the entire image is balanced in exposure, and they can tell you if there are overblown highlights being clipped, etc. Does that actually tell you if the image is properly exposed? No. You might have overblown highlights in a perfectly exposed image, for instance. Half your image may be overblown, if your subject is exposed properly. An overblown white background is very common goal in commercial photography, in fact.

    Maybe your histogram has clipped shadows and is heavily weighted to the left (dark, or underexposed image according to histogram reading). Yeah, that could be a "low key scene", where you want to preserve the darkness in the shadows. Who is to say except a human eye?

    In other words, histograms and software can tell you a lot of useful and important information, but they can't tell you if an image is "properly exposed".
    • Like Like x 2
  7. I take it on an image by image basis. Histograms are useful tools, but I'm sure that you could run them over a lot of great images that are very appealing to the eye and they'd tell you that the image is under/overexposed and needs fixing.
    • Like Like x 1
  8. Alanroseman

    Alanroseman Super Moderator Emeritus

    Dec 21, 2010
    New England
    NED - +1
    Luckypenguin - +1
    • Like Like x 1
  9. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    Very Simplistically,

    For me, if the image does not require any exposure compensation in post (lightening or darkening) then it's properly exposed.

    How you exposed and what you exposed for also has great bearing. Say you metered and shot for a subject that was in the shadows ... then the area which is not in shadows will be over exposed requiring exposure compensation in post. Et cetera.

    • Like Like x 1
  10. SMaturin

    SMaturin Mu-43 Veteran

    Apr 30, 2011
    New York's Backyard
    It is a matter of technology catching up with evolution.

    The problem is that our eyes can see orders-of-magnitude greater variation in light and color intensity than any film or electronic sensor yet developed.

    When you are out on a sunny day, you have no trouble seeing the details of both the shadowed bark on a tree and the brilliant reflections of the sun off of water. Both at the same time. You can see detail in both bright sunny days and starlit nights that no camera yet developed could ever hope to achieve. Our visual systems, from the muscles that control the iris (f-stop of the eye), the lens muscles (autofocus motors), the retina (sensor), the optic pathways and visual cortex (onboard processor), and the neocortex that interprets the image, have all evolved over a couple of billion years to be incredibly effective and sensitive to all ranges of light available on planet earth. Our hundred billion neurons do a much better job of filtering, compressing, and interpreting the raw data compared to silicon chips.

    So the correct exposure is the one that looks right to tell the story you wish to tell in your photograph.

    How do you capture it? Well, that is the art and science of photography, which has only been around for a couple of hundred years, rather than a couple of billion. Again, orders of magnitude difference.

    I think everyones' answers above are helpful. With experience, we get better at guessing what settings will give us the result we wanted. But shooting RAW, and bracketing when in doubt, make it a lot easier to correct later when you guessed wrong. This is an advantage of digital over the older technology of film. Shoot more exposures than you need if you are not sure how the lighting situation will work when compressed into a digital image, and sort it out in PP. That was expensive and much more time-consuming with film, compared to digital.

    Learning how to interpret the histogram and the metering of your device is essential. But our devices are so complex today, able to do so much, that the learning is a constant process. Shoot extra exposures at different settings and learn from playing with them.

    Try HDR processing with bracketed exposures to see what the camera misses that you assumed was there because you could see it. I have learned so much from that process.

    • Like Like x 1
  11. Djarum

    Djarum Super Moderator Subscribing Member

    Dec 15, 2009
    Huntsville, AL, USA
    Alan, now I feel left out ;) 

    They said what I tried to say but failed to articulate it.
  12. Hyubie

    Hyubie Unique like everyone else

    Oct 15, 2010
    Thanks everyone. Just wanted that confirmed. Need to train my eye some more. :wink:
  13. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    And have a calibrated monitor...
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