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How much can I pull out of a RAW file if under-exposed?

Discussion in 'Image Processing' started by bjurasz, Oct 1, 2015.

  1. bjurasz

    bjurasz Mu-43 Veteran

    Dec 10, 2014
    Cedar Park
    I've got an E-M10 and wondering, if I shoot in RAW and underexpose the shot on purpose how much I can compensate in post production? 2 stops? 3 stops? Shooting some car interiors, which is not always possible to do with a tripod. Would rather increase the shutter speed to alleviate camera shake and adjust the exposure back in post. Just wondering how far I can push it. Thanks!
  2. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    You'd be better off just raising the ISO in most situations. "Pushing" in post is only advantageous when you only want to lift the shadows without raising the highlights.

    "Pushing" in post produces the same noise as raising the ISO and doesn't compensate for other alterations in the image that are generally done automatically when the ISO is raised.

    How much you can "push" in post is largely dependent on the ISO you've used. The lower the ISO the more you can "push". At the highest ISOs you can't successfully "push" to any significant degree. Final output size (read: print or display size) and the amount of shadow noise that you'll accept are also major factors.
    • Agree Agree x 5
  3. gryphon1911

    gryphon1911 Mu-43 Hall of Famer Subscribing Member

    Mar 13, 2014
    Central Ohio, USA
    And that is the real kicker here. It all depends on what you are willing to accept and the desired end result.

    For example, I can be happy with pushing ISO 200-800 files 2-4 stops if my end result is B&W, whereas with color images, it's more like 1-2.
    If you know you are going to be running into some high DR situations, still shoot RAW, but I would bracket, do a +2/-2 set. Then you can merge the best of all the images together. That is if the subject allows for that kind of post work. Not all do.
  4. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    It's not only how much noise you're prepared to accept. You've also got to factor in what processing software you're using and how skilled you are at using it. Both of those things make a difference.

    Also, are we talking about global shadow recovery or local shadow recovery? You don't have to apply your shadow recovery processing to the whole of the image and while whether you apply it to the whole image or just one part of it is probably not going to make a difference to how many stops you can recover, it can certainly make a difference to the appearance of the final image. Strong noise reduction may be nowhere near as visually objectionable in an image if it's applied carefully in shadow areas than it might be if you apply it to the whole image.
    • Agree Agree x 1
  5. pellicle

    pellicle Mu-43 Hall of Famer Subscribing Member

    Feb 10, 2010
    Killarney, OzTrailEYa
    If you own a camera, why not just try and see?

    The answer will depend on a number of factors (how far and how the camera records to start the list ...)
  6. pellicle

    pellicle Mu-43 Hall of Famer Subscribing Member

    Feb 10, 2010
    Killarney, OzTrailEYa
    Especially if you choose the green channel as that was made with twice the pixel count

    • Like Like x 2
  7. What kind of car interior shots? Can you exposure bracket it instead of pushing a single shot? I don't do that kind of stuff much at all but the one time I had to make bracketing work (with Enfuse for LR) I was pretty happy with the results -

  8. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    Tip: for car interiors, try a short inverted tripod held to the roof.

    If you are serious, though, off-camera lighting or flash is almost essential for car interiors. They don't lend themselves well to point-and-shoot, because the natural lighting is usually terrible.
  9. bjurasz

    bjurasz Mu-43 Veteran

    Dec 10, 2014
    Cedar Park
    Arg, that was a great idea with the tripod upside down! Usually I can't think of any way to stabilize a camera inside a car. But I think you're right about needing off camera lighting. Underexposing to get shutter speeds up is not the right approach after all.
    • Like Like x 1
  10. 50orsohours

    50orsohours Mu-43 Hall of Famer

    Oct 13, 2013
    Portland Oregon
  11. dancebert

    dancebert Mu-43 Veteran

    Jan 18, 2014
    Hua Hin, Thailand
    It depends. In my tests with my worst lens (O12-42ez) the worst result I had was recovering some texture at 2 stops. Most of time 2 stops gave a usable image, though my standards for usable might not be yours.

    Try the 'paper towel test': https://www.mu-43.com/threads/65737/
  12. m4/3boy

    m4/3boy Mu-43 Veteran

    Jul 21, 2013
    Under exposing anytime is never a good approach. Use a tripod, add lighting or bump the ISO - but don't underexpose!
  13. Dave Jenkins

    Dave Jenkins Mu-43 Veteran

    Actually, someone on another forum did a test on this some months back and found there is very little difference between files where the ISO is increased before the exposure and underexposed files that are corrected in a post-processing program. Wish I could provide a link, but I've forgotten where I saw it.

    One very good reason for raising the ISO in advance, however, is that it allows you to use a more optimal shutter speed and f-stop.
  14. m4/3boy

    m4/3boy Mu-43 Veteran

    Jul 21, 2013
    I don't buy that for a second, experience has taught me otherwise; but believe what you wish.
  15. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    This is sensor dependent. Sony sensors (I don't know if it's all Sony sensors) are ISO-less. Other sensors are not and under exposure is not a good idea.
    • Agree Agree x 2
  16. Dave Jenkins

    Dave Jenkins Mu-43 Veteran

    Just reporting what I read. You guys do as you wish.:D 
  17. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Naw, there's sensor based gain. It maxes out at 3200 though with current sensors, anything past that is software based pushing (the files will be shot at 3200, and pushed in camera).

    The only cameras I can think of that benefits from pushing the base ISO are some Leicas, this is purely because of a programming error however (as you increase the ISO it massively increases the (lossy) compression resulting in vastly less detail and banding, base ISO is uncompressed and actually retains more detail and generally far less banding).
  18. mcasan

    mcasan Mu-43 All-Pro

    Feb 26, 2014
    Using DxO Optics as the raw converter....more than with Adobe raw converter.
  19. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    When I made my initial response some time ago I'd forgotten I posted an example of before and after processing late last year in the thread on that topic. I'll add the link to that post here since it's relevant:

    SHOW: Before and After Shots | Mu-43.com - Micro Four Thirds User Group

    If the link opens at the top of the page, my post is at post #10.

    As you can see from the before image, everything but the sky is severely underexposed. The brightest parts of the clouds are just short of clipping and my exposure was based on not clipping those brightest highlights. Bringing up the underexposed area just by adjusting the exposure slider really blows the sky out but if the highlights aren't clipped in the original file you can always recover the detail there in processing. It's your choice whether you do the basic processing so that you keep detail in the highlights and open up the rest of the image or bring up the underexposed areas and then bring the highlights down in tone later. Either way you end up having to process for one part of the image and then work with local adjustments for the other part of the image. Sometimes doing the basic processing for the highlights seems to work best for me, sometimes doing the basic processing for the darker areas works best. Things tend to be a lot easier if you aren't concerned with blowing out the brighter areas and just want to bring up the darker areas. Getting detail in both makes things trickier and it's harder to get a really good result when you've got 2 areas that really demand different processing in the same image. There's a learning curve to get over and if you're only working in a RAW converter like Lightroom and not using a program like Photoshop as well, there's no way of applying optimum processing to both areas.

    I still go back and work at this image again every now and then and I'm currently happy with a version that doesn't lift the underexposed area quite as much, not because of any noise related issue but because I think it gives a better "mood" to the image. How far you pull the underexposed area up in an image where you want detail in both the highlights and shadows is probably going to end up coming down in part to the mood you want to convey if you're trying to produce a natural looking result because you aren't going to be able to get equally good results in both areas from a single file.

    In the end results are going to depend on how much the underexposed area is underexposed by, how bright you want that area to end up being, and how much detail you want to keep in the part of the image which isn't underexposed. That last bit is really the important point because it determines your exposure. You can't recover detail in clipped highlights so the limit on your exposure is how far you can go without clipping the highlight detail you want to keep.
    • Like Like x 1
  20. Replytoken

    Replytoken Mu-43 Hall of Famer

    May 7, 2012
    Puget Sound
    And IIRC, there are some (older) sensors that have less noise at ISO's higher than their base. I have read so much on this topic that I forgot where I saw the charts that showed ISO vs S/N for various sensors. I am somewhat partial to Sony sensors and that is why I like having an E-M5 along with my E-M1. They are both great sensors, but each has it own attributes that sometimes come in handy in certain shooting conditions.

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