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Has anyone tried this?

Discussion in 'Image Processing' started by Maczero, Jul 26, 2011.

  1. Maczero

    Maczero Mu-43 Regular

    141
    Feb 13, 2010
    Fife
    I have no idea if this has been discussed before, but I have a basic image adjustment technique that I use no matter which application I am using to process my photos and no matter whether they are Raw or JPEG. It is pretty obvious, so I expect brickbats if it has been covered before.

    The basic premise is that negative EV is often required to protect the highlights with a m43 sensor. However, assuming that the metering system is assessing the image as a whole correctly (not the case in snowy scenes etc) the resulting image is darker the it should be. The answer: apply an equal and opposite exposure adjustment to the image. This may well result i blown highlights, but because they were captured in the original image and only blown in post they can be easily recovered. Err, that's it.

    It works particularly well with Aperture's extended and stacked curves, but I have also used it in LightRoom. It's an agnostic technique and provides a useful starting point to further adjustments.

    Andrew
     
  2. WT21

    WT21 Mu-43 Hall of Famer

    Feb 19, 2010
    Boston
    Or adjust the EV in camera

    Your camera's metering system is trying to balance the overall image to mid level gray. That is, it sets the shutter speed, ISO and/or aperture to make the scene balance to neutral gray. So, if the scene is all white, the metering system will make it appear darker (pushing thhe exposure to middle gray, which is darker of course than pure white). So, for a snow scene, you should push your cameras EV to + 1 or even +2 to force the camera to expose to something above middle gray.

    Of course, you could make this adjustment in post, but the issue there is that if you do have any dark parts in the scene, they will be way under exposed, and will look horrible if pushed in post, because dark areas in digital cameras that are lightened in post show sensor noise more easily, and one to two stops will really show poorly. They'll look a bit better if metered in the way described above, at the scene, and then you could just "lighten shadows" by a partial stop to bring out shadow details.

    Another trick is to use your live view histogram and expose to the right. That is, have the live view historgram up, and push EV up or down, to make the scene expose as close to the rit side of the historgram without going over. This, by the way, can often result in too-bright images, but the trick in digital is that too bright images brought down in exposure in post look MUCH better than too dark images brought up in exposure.
     
  3. Maczero

    Maczero Mu-43 Regular

    141
    Feb 13, 2010
    Fife
    I agree with all that you said, but that wasn't the point I was trying to make. The fact is that we often do need to underexpose to preserve highlights. Once they are gone, they are gone - especially when shooting JPEGs. My experience is that it is generally better to preserve highlights. This was just meant to be a simple technique for starting the image processing off by getting to the right general luminance level.

    Andrew
     
  4. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Northumberland
    I preserve highlights by bracketing (most of the time) and rarely get a picture where I'm stuck with totally blown clouds & stuff ... except in my e-410 where it won't bracket wide enough for the sensor limitations. In that case I do underexpose and take another picture.

    I like your use of the word 'Agnostic' ... whatever you mean by it. :)

    There is a looming problem with your technique regarding some Olympus cameras in that the E-30, e-620 and others can create noisy shadows, which if pulled up in post processing give the impression of way too much noise. Of course if blown highlights are your only concern, then everything's fine.
     
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  5. WT21

    WT21 Mu-43 Hall of Famer

    Feb 19, 2010
    Boston
    Sorry. I guess I misunderstood. Yes, to preserve highlights, you could neg exposure comp at the time of pic, and then bring back in post. However, as Ulfric and I noted, you are gambling, in that shadows brought up in digital cameras tend to fall apart.

    My personal approach is to recompose, to get a little less DR in the photo (say, move around to get rid of bright sky in the background), or I will also often choose to blow highlights (like a small patch of white sky, if I can't compose it out), to get a better exposure on the subject/rest of the image.

    This is one of the challenges of a more relatively limited DR camera like m43. My 5D for instance, can recover about 3 stops in post in the highlights, whereas my EP1 only does about 1-2.

    It's also a reason to shoot RAW in this case, as the recoverable DR in jpgs is much more limited, and even if you can bring the detail back, the color data is gone, and the tonalities don't look as smooth when recovering a jpg shot.
     
  6. zpierce

    zpierce Super Moderator

    661
    Sep 26, 2010
    Minneapolis, MN
    Zach
    I did this all the time early on, thinking it was a no brainer, until I discover the previously mentioned problems in the lesser exposed areas. I noticed that the problem extends beyond the shadows as well, maybe not as obvious, but even slightly under exposed faces don't look great when pushed in post. My typical method of operation is to let the camera decide, then push it up or down based on what's most important to me in the photo. If I'm taking a backlit shot of something, especially a person, I'll let the sky get blown to get the subject right. However if it's a high DR landscape shot for example, I'll probably shoot for a compromise and push as much as I can in post so I can have a decent looking sky. If it's a scene where the highlights are the subject, then I'll expose for that and forget the shadow or apply more NR in post. Bottom line is I have found in my experience that a one size fits all approach just doesn't work and you just need to be cognizant of what's important to you in your frame and expose accordingly given the DR capabilities of the camera. I rely heavily on the highlight feature. Often I push it as much as I feel I can on the camera until something important gets blown out (starts blinking) then I back off a step. Often times it's making a tough call because you frequently have to give something up.
     
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