Noisereduction by shooting to the right and adjusting?

Discussion in 'Photographic Discussions' started by Garbz, Nov 26, 2009.

  1. Garbz

    Garbz No longer a newbie, moving up!

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    This is something that pops up constantly. The idea that if you shoot to the right and then adjust your image in post processing it acts as a sort of a noise reduction.

    This irked me as it goes against everything I could think of with using a camera. Mainly what got me is the idea of overexposing. If you can over expose then you can also just simply drop your ISO. I have long believed That the step change in noise at the high end of the ISO scale of cameras is very severe indeed. The noise increase is somewhat linear towards the bottom scale from the common graphs, but seems to rise exponentially after a certain point, and that is usually the point where noise starts to matter in an image.

    After a while of trying to justify to myself that reducing the brightness of an image constitutes less of an improvement than reducing the ISO I gave up, and grabbed my camera. I present to you the results of my test:

    Below are two images of my slightly cream wall, on the edge is a black picture frame, and everything is nicely out of focus to make damn certain that noise isn't mistook for detail.

    The first image was shot at ISO800 1/6th f/5.6. The second image was shot at ISO1600 1/6th f/5.6 and reduced in brightness in Lightroom 1.0EV. A quick sanity check was done to check the brightness of the image so it's unchanged and over a 31x31 pixel average which gave:

    ISO800 rgb(147,148,130)
    ISO1600 rgb(146,147,131)

    Wait ok firstly the colours no longer match! I want to go back and give this a go with a colour checker card to see how bad it is, but really right now I will assume that this slight difference isn't field relevant.

    The images: ISO800:
    [​IMG]

    ISO1600 -1EV adjusted:
    [​IMG]


    Results:

    Ok so the ISO1600 shot did get better when reduced. That was expected, but the point is to find out how much it got better by. To do this the left quarter of the frame was selected in photoshop. The histogram was set to extended information on the colour channel and the following standard deviations were noted:

    ISO800 vs ISO1600
    Black area:
    4.52 vs 4.79
    Light area:
    8.31 vs 8.40

    Then the measurements were repeated with the histogram set to luminosity:

    ISO800 vs ISO1600
    Black area:
    3.38 vs 3.64
    Light area:
    2.48 vs 2.89


    Now there is an uncertainty in that I'm not sure how very "scientific" the results from photoshop could be trusted. I'm inclined to believe they represent the images, but I'm not sure how much meaning the numbers have.

    However I satisfied my own belief that if you're in a situation where it is possible to shoot to the right and then underexpose in post, you may well be better served dropping your ISO to just simply expose correctly. Noise wise the differences favour the lower ISO shot, but looking at the images it really seems like this discussion isn't worth having :lol:

    Now one other thing I noted earlier is that the noise response of cameras typically change depending how close to the end of the ISO scale you actually get. This result here for the Nikon D200 between ISO800-1600 will likely not match the results on a Nikon D700 between ISO800-1600 (and the overexpose underprocess trick may work), however I would bet the results would match a D700 ISO12800-25600.

    Let's hear from other people. What are your experiences? Perhaps if someone else could repeat this test on a different camera?
     
  2. Tighearnach

    Tighearnach TPF Noob!

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    I always thought the idea of exposing to right was to preserve as much highlights as possible. I thought it was shooting in iso 100 for example take a correctly exposed shot and then reshoot the shot still in iso 100 exposing to the right (plus 1 EV for example) but without clipping any highlights. I did not realise it was for noise reduction or that you would shoot in a different ISO. Am I way wrong in my thinking?
     
  3. Garbz

    Garbz No longer a newbie, moving up!

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    No you're right by my reckoning.

    It's just recently I have seen people use shooting to the right in conjunction with ISO3200 shots saying when they shoot to the right and then adjust in post they get less noise. I am here arguing that they may be better served by lowering the ISO and shooting at the correct exposure.
     
  4. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    Ever since you raised this issue, I've been thinking about this. I did a little quick experiment this morning.

    Here's the setup:

    D300
    50mm 1.8 lens
    ISO3200
    Single CF 60 watt bulb, minimal ambient light

    Here are the two pictures, and I'll refer to them by number throughout:

    ==1 Full (1F)==
    Image exposed "properly", metering off the car. Dead-center on the light meter.

    [​IMG]

    ==2 Full (2F)==
    Image overexposed somewhat (3 or 4 markings overexposed on the light meter), same metering point.

    [​IMG]

    ==1 Cropped (1C)==
    At 100%...

    [​IMG]

    ==2 Cropped (2C)==
    At 100%...

    [​IMG]


    Now the key here is I kept the number of variables down to 1. The exposure. I did this because it illustrates ONLY that exposing more with the same ISO does reduce the noise (as you can see in the 100% crops).

    Now what you've been saying is "just knock down the ISO!", but what I realize now that I think you've been missing is that there are often cases where you just can't. Sometimes you have a situation where the lighting is so dark that you cannot GET a proper exposure on a lower ISO (say 200-800), and at these points you get pushed up into the higher ones... and it is in these cases that people suggest exposing to the right because it reduced the noise in an essentially unavoidably noisy situation.

    This is amplified if you have a long focal length because you need the fast shutter speed to compensate. This is really common for people doing indoor sporting events, taking pictures of their kids on stage at plays, etc.

    I'll admit that I don't feel like this is a complete thesis, but I'm hoping with a few times back and forth that we'll figure this out. :)

    Of course we should be doing this on the other way better forum, but I suppose there are more people here to refute your evil claims. :)
     
  5. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    I would also like to say... maaaaaaaaaaaan my camera handles high ISO well. :lol:
     
  6. DScience

    DScience No longer a newbie, moving up!

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    Yea for real!

    I wonder how well the D300s does compared?
     
  7. Garbz

    Garbz No longer a newbie, moving up!

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    See this is my point. If you're forced to use HighISOs because of poor lighting then how do you expose to the right? My aperture is as large as it will go, my shutter as slow as sharpness will allow and my magical imp is on holidays :)
     
  8. Dwig

    Dwig TPF Noob!

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    Exactly. If the correct exposure at ISO 1600 is f/2 @ 1/60th then:

    "Expose to the Right" 1 stop would yield f/2 @ 1/30th

    and

    Correct exposure (+-0 EV) at ISO 800 would be f/2 @ 1/30th.

    The two methods end up with exactly the same f/stop and shutter speed. Therefore if you can to "Expose to the right one stop" then you can use a one stop lower ISO just as easily.

    Either way, none of this is "noise reduction". It would be more properly termed "noise avoidence". You can't "reduce" what you don't record in the first place.
     
  9. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    Isn't that just the thing, though? You're exposing more to the right so that you make sure you expose as much as you possibly can (mostly adding more detail to darker areas of the frame) and then back the whole thing down to restore your shadows. By the way, I also use this method in low ISO in night photography with stunning results.

    BTW, if you're adding exposure compensation, I think all you're doing is exposing more anyway, thus the same result, just different numbers. C# vs. D flat.

    And Garbz... the point is if you're already at a point where you're into high ISOs... push the ISO a step higher so you can use this method. If you're at 1/60th of a second on a 200mm focal length, and would need to go to 1200ISO to make it fast enough to do 1/200th of a second or so, then push it to 2000iso or so and LEAVE it at 1/200th of a second. Bring out the detail in the shadows, back it down in post-processing and whamo. Less noise.
     
  10. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I'm sure many of you have read this already...but here is the article that I often reference when advocating the 'Expose to the Right' technique.
    Expose Right

    My personal experience is that it's not always a matter of 'shoot to the right'...but more of a 'don't shoot to the left'.
    An interesting addition to the test shots, would be a shot that was one stop under exposed, but then brought up with software. My guess would be that it would show significantly more noise.

    Now remember that noise is more likely to show up in dark areas...and a typical image might have a range of tones, some being fairly dark even when the overall shot is well exposed. It's fairly easy 'bring up the shadows' with software, but that is where you are likely to bring out the noise. So by exposing a little brighter than you want the final image to be...you are essentially exposing for the shadows and editing for the highlights and/or mid tones.

    That's my take, for what it's worth.
     
    Last edited: Nov 27, 2009
  11. Garbz

    Garbz No longer a newbie, moving up!

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    manaheim are you now talking about shooting to the right to some other ends? Or are we still talking about the resulting noise?

    Obviously I fully agree shooting to the right has some advantages in post processing, and I condone it from that point of view. I raised this topic on the point of "shooting to the right" is not as good at mitigating noise (and only noise) as dropping the ISO.
     
  12. manaheim

    manaheim Jedi Bunnywabbit Staff Member Supporting Member

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    I don't think we'd disagree on that point as long as you had the option to get the image you were looking for without dropping the ISO into a range that would still be reasonably noisy.

    :lol:

    I think we just need to get together and have a beer while we work this one out. :)
     

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