overexpose vs. underexpose

Discussion in 'Digital Photography' started by Ridge08, Feb 22, 2009.

  1. Ridge08 macrumors member

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    #1
    If you compare highlights overexposed by one stop with shadows underexposed by one stop, is the same amount of detail lost in each case?

    If I adjusted the exposure for each on the computer later, which edit would introduce the most noise?
     
  2. bloogersnigen macrumors regular

    bloogersnigen

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    #2
    With digital you want to err on the darker side (underexpose)
    With film you want to err on the lighter side (overexpose)

    I'm assuming this is why you asked the question
     
  3. namethisfile macrumors 6502a

    namethisfile

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    #3
    i would say that for the first question that you'd probably lose details on the highlights. underexpose shadows are more recoverable than overblown highlights, generally speaking

    to my understanding, i don't think you can add noise by adjusting the exposure in post. it depends on your source. brightening it up might make it more apparent, but it's always been there. so, the answer is no.
     
  4. arogge macrumors 65816

    arogge

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    #4
    Overexposed highlights are lost more-easily than underexposed highlights, and overexposure is often unrecoverable without a significant loss of image quality.
     
  5. toxic macrumors 68000

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    #5
    RAW will give you about 1 stop of highlight recovery. Dunno about shadows...you can't bring out details that were never resolved in the first place. Anyway, expose to the right, just don't clip.

    Underexposing and raising exposure will enhance noise, but it won't be an issue if the photo was in the lower ISOs to begin with. At higher ISOs, get it right the first time.

    As for film, certain films don't respond well to overexposure, but I think most had more tolerance for it. At least color, anyway. I don't have that much experience with film.
     
  6. Doylem macrumors 68040

    Doylem

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    #6
    Under-exposure? Over-exposure? Why settle for either in this digital age, when it costs nothing to 'bracket' your shots? And shooting RAW gives more latitude still...
     
  7. mattyb240 macrumors 6502a

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    #7
    I agree being new o cameras I find bracketing crucial in some shots as I am still learning about where to take the best metering. Plus sometimes I prefer the slightly underexosed!
     
  8. Ridge08 thread starter macrumors member

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    #8
    Doylem,

    I do try to get the right exposure! In part, the question was an academic one posed out of curiosity.

    But if I`m shooting a high-contrast scene, it`s nice to know whether it`s better to be fixing a slight over- or underexposure. And wouldn`t the same be true if the lack of a tripod on one occasion (and lack of an automatic bracketing function on the D40) make bracketing much slower and trickier?
     
  9. toxic macrumors 68000

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    #9
    bracketing shots of moving subjects doesn't work, in case you haven't noticed. RAW only gives you some latitude.

    so again, expose to the the right, just don't clip the highlights.
     
  10. ChrisA macrumors G4

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    #10
    No. You can recover shadows that are under exposed by one stop in post processing but blon out highlights are "gone". The best exposure for digital is to expose as much as you can but ithout blowinghighlights except for source of light and reflections of same. This assumes you will adjust the images.)

    Shooting digital is just like shooting slides. Once a highlight has burned clear to "film-base clear" there is no way to recover. Color and texture is gone. But "thick" slides can printed through in the darkroom. Digital is exactly the same. The dark shadows will be under exposed but at least there is some information there
     
  11. Edge100 macrumors 68000

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    #11
    My $0.02...

    Never overexpose. Yes, shooting in RAW allows you to recover about one stop from blown highlights, but this is really a last resort; you really should avoid blowing the highlights in the first place.

    On the flip side, underexposure will produce noisy pictures when corrected for exposure, especially at high ISOs. However, most modern DSLRs are pretty good at reasonable ISOs, so this may be less of a problem than you think.

    My advice: expose to the right, but never touch the right side of the histogram. If you think you will, choose to either underexpose or bracket your exposures.

    At 0EV compensation, my 1DmkII routinely takes pictures that are about 1/2-stop underexposed, even with evenly-lighted subjects. So I usually shoot at about +1/3EV, even though the mkIIs fairly good DR and noise performance doesn't require it.
     
  12. Edge100 macrumors 68000

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    #12
    This is a good point; if you think of digital like you think of slide film, you wont go wrong. In terms of DR, it goes print film>digital>slide film, but if you consider digital = slides, you'll never go wrong.
     
  13. Kronie macrumors 6502a

    Kronie

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    #13
    Underexpose. When those highlights are gone, there gone forever. You can also push and underexposed raw file quite a bit.

    Ideally you want to nail the exposure but I seem to rarely do. I'm sure its my camera and not me, right?:D
     
  14. CrackedButter macrumors 68040

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    #14
    Some of use don't shoot landscapes dude!

    Saying that, the time will come when cameras can 'auto bracket'. Ricoh are releasing a camera that tries such a thing with the CX1 by combining 2 images and merging them in camera.
     
  15. Edge100 macrumors 68000

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    #15
    Admittedly, this is splitting hairs, but I think the best way to say it is "never overexpose". Don't purposely underexpose (since that leads to other problems), but if the choice is clipping highlights or getting noisy pictures because you had to bring out the shadows in PP, I'd take the latter every time. Clipped highlights are far more intrusive than a little luminance or chroma noise.
     
  16. Kronie macrumors 6502a

    Kronie

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    #16
    I don't think you really need it.
    I have had awesome results just tweaking the exposures from one Raw into three or four TIFF's.
    For most stuff its just as good as bracketing on my 40D.
     
  17. arogge macrumors 65816

    arogge

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    #17
    Bracketing won't work for moving subjects, and every frame "click" does actually cost money. A person still needs to decide which bracketed frames to use and which to delete, and when bracketing can increase the number of files by 3X or more, somebody is paying for those excess files to be processed. It would be nice if the computer could automatically identify all of the unwanted shots, but until that is available, any culling must be done manually.

    I can fix underexposure and recover highlights, but it is difficult to recover blown highlights that were caused by overexposure. Even with 14-bit recording, I still only get about 1 EV of recoverable highlights before my exposure error becomes very noticeable.
     
  18. Edge100 macrumors 68000

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    #18
    Bit depth doesn't increase DR. Most DSLRs have ~9-9.5 stops of DR (that is, the difference between the darkest and lightest things the camera can resolve), irrespective of bit depth.

    What increased bit depth WILL do for you is make it less important to expose "to the right". To illustrate:

    - in a 12-bit linear system, you have 2^12 (4096) levels of grey per channel, of which half (2048) lie in the range of pure white to middle (18%) grey, 1024 lie in the next stop, and so forth. In the last stop before pure black, you have only two levels of grey, which doesn't leave much ability to describe detail.

    - in a 14-bit system, you have 2^14 levels (16384) of grey per channel, of which 8192 lie between pure white and middle grey, 4096 lie in the next stop, 2048 in the next stop, and so on. The last stop between black and just-above-black is still only described by two levels (one bit), but the difference between black and "just-above-black" is much smaller on the 14-bit system. We havent said anything about what the camera considers pure black, which does speak to DR.

    What this means is that for a 14-bit sensor, you can expose 2 full stops lower and still retain the same resolution as in a 12-bit system; that is, exposing to the right on a 14-bit sensor is much less necessary than on a 12-bit sensor. The DR has not increased, but your ability to resolve differences has increased and your noise floor has decreased by two stops. This isn't an increase in DR, per se, but a lowering of the noise floor; your s/n ratio has increased.
     
  19. Ridge08 thread starter macrumors member

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    #19
    Everyone, thanks for your posts!
    Edge100, that sounds interesting. Just wish I more fully understood what you were talking about!
     
  20. Edge100 macrumors 68000

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    #20
    All it means is that exposing to the right "uses up" the bits; you have more levels of grey to express differences.

    This becomes less and less important as you increase the bit depth of your sensor.
     
  21. Ridge08 thread starter macrumors member

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    #21
    The consensus seems to be that underexposed shadows are less sinful than blown out highlights. But if the brightest tones account for most of the data recorded by the sensor, does that mean you should get as close to overexposed as possible without actually overexposing?

    If that`s the case, then presumably you`d record the most data possible, but even if not blown out, the picture would still be be too bright, right? So then you darken it on the computer?
     
  22. toxic macrumors 68000

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    #22
    yeah. hence, expose to the right. this is especially important when shooting at high ISOs, since raising the exposure afterwards will increase noise noticeably.
     
  23. Edge100 macrumors 68000

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    #23
    Yes. The #1 rule of digital photography (and, in fact, of ALL analog-to-digital processes...audio recording being another prime example), is "use the bits, but do not clip". For photography, this means exposing to the right as much as possible, without clipping the highlights. This gives you the absolute maximum achievable signal-to-noise ratio for a given sensor.

    As I mentioned, as bit depths go up (from 12-bit to 14-bit, for instance), this becomes less of a concern (since each bit gives you an additional stop of increased resolution), but it's still good practice to maximize the s/n ratio. Bit depth has nothing to do with dynamic range, per se, but rather the resolution with which the dynamic range is digitized.

    If the photo is overexposed (from an artistic sense, not a technical "clipped highlights" sense), you can always reduce the exposure later on; bits can be thrown away, but can never be added. Hence, you always want to collect as much data as possible. Increasing exposure later on will always add noise; whether that noise is visually objectionable is another matter, but you're always better off, as a rule, throwing away data than trying to add data back.
     
  24. Edge100 macrumors 68000

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    #24
    Absolutely.

    At high ISOs, it's really, really import to get the exposure correct. In fact, I think that a lot of what people find objectionable with high ISO photos is not actually the result of the noise inherent with high ISO, but rather of the fact that the shots are underexposed (which is really easy to do when light is very limited). I've seen properly exposed ISO 3200 shots from modest cameras (think Canon 20D) which produce fine looking JPEGs and prints; there is noise for sure, but it doesn't spoil the photo.
     

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