Thread: Getting footage from +1 or +2 to 0 in prores

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  1. #1 Getting footage from +1 or +2 to 0 in prores 
    Hey people,

    I always wondering what your exact workflow is to get on purpose overexposed footage to normal exposure. (never shot raw, I guess there it is simple by changing the exposure in resolve, I am talking Prores)

    I mostly take the LOG controls and turn the offset down so my midtones are back where I want them and almost always have to raise my shadow control. (which is odd, I shot the same thing with normal exposure and my shadows do not sit that low like they sit when pulling the exposure down in a +1 or +2 shot)

    What's the standard approach to get +1 to 0?
    Just wanna make sure I am not missing something.

    Thanks people.
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  2. #2  
    I mean, if you over expose in camera and you're shooting a rasterized codec then you should lower the sensor's ISO so that the image is properly distributed and not slammed to one side of the data range. If I didn't do that though, then I'd have to use the lift/gamma/gain controls to get everything where I wanted it to be.

    Remember, you only get to encode an image once--make it count.
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  3. #3  
    Senior Member LochnessDigital's Avatar
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    Yeah, I would advise "baking in" that pull down. If you're shooting a stop over, pull it back down to neutral with ISO 400.

    But since you didn't, you can use LUTCalc and make a LUT with an exposure compensation built into it.

    I'm not a colorist, so I'm sure a real one will chime in about a way to do it mathematically without the use of a LUT.
    Aaron Lochert
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  4. #4  
    But you are both talking RAW don't you? May be I am missunderstanding, but do you propose shooting at ISO 800 and in Resolve change the ISO to 400?
    Will look into LUTcalc thanks!
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  5. #5  
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    The Offset control moves *everything*, so if you bring down mid-tones, shadows have to go somewhere. Just bring them back up with another control; you haven't destroyed them by shifting their position.

    However, instead of using Offset for positioning mid-tones, try using it to set black levels. Then use other controls to position mid-tones.

    As you note, ISO is only changeable with raw footage.

    Why you would need LUTcalc for something Resolve does itself, I have no idea.
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  6. #6  
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    Assuming you've shot log on a BM camera, use the corresponding BMDFilm/BMDFilm4K/etc to Linear lut, adjust the gain control (gain in linear mode = exposure compensation), then back to BMDFilm/BMDFilm4K/etc with the corresponding reverse lut.
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  7. #7  
    When you're shooting in CinemaDNG/raw (on most cameras), ISO is just a metadata flag. All it does is shift the middle grey point up the scale (lower ISOs) or down the scale (higher ISOs) so that the linear data is interpreted differently during the demosaic process. You can change that flag in camera or in post because, again, it's just metadata.

    When you're shooting a rasterized codec, like ProRes, your ISO setting is baked in during the camera's encoding phase. The benefit of adjusting ISO on a shot by shot basis is that you're making sure that the scene's relevant information is encoded where you want it to be, so that--if you're adjusting it later with LUTs or heavy grading--you can fight the effects of compression. Working with rasterized codecs is all about making sure you get as many things right on the day so that you don't have to push too hard to get your desired vision in post. How does this work practically?

    If you want to over expose the BMPCC by +1 stops, set it to ISO 400. +2 = ISO200.

    If you have to under expose to protect the highlights--say, by -1 stops--set the ISO to 1600.

    This ensures that you're not pushing around the codec too hard when you're grading. ProRes HQ is a great codec, but it's not impervious.
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  8. #8  
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    Quote Originally Posted by Alex.Mitchell View Post
    When you're shooting a rasterized codec, like ProRes, your ISO setting is baked in during the camera's encoding phase.....

    If you want to over expose the BMPCC by +1 stops, set it to ISO 400. +2 = ISO200....

    ProRes HQ is a great codec, but it's not impervious.
    Surely you're not advising the OP to set the camera at 400 or 200, when shooting Prores Film? Then again, he's never revealed what camera he's using. I had assumed the BMPCC, but who knows.
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  9. #9  
    Quote Originally Posted by jrd View Post
    Surely you're not advising the OP to set the camera at 400 or 200, when shooting Prores Film? Then again, he's never revealed what camera he's using. I had assumed the BMPCC, but who knows.
    I am indeed doing just that. If you're going to expose to the right, lower the ISO so that everything is mapped out in a way that requires the least adjustment in post. This is a best practice when shooting any digital camera...
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  10. #10  
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    Quote Originally Posted by Alex.Mitchell View Post
    I am indeed doing just that. If you're going to expose to the right, lower the ISO so that everything is mapped out in a way that requires the least adjustment in post. This is a best practice when shooting any digital camera...
    If a BMD camera like the BMPCC or BMCC is rated at 800 ISO, lowering the ISO in-camera for Prores Film mode degrades the image and gains the shooter nothing. There is no analogy to film stock.

    Lowering the ISO simply lowers the clipping point of the highlights (e.g., highlights which clip at 100% at IS800 will clip at 90% at IS400 and at 80% at ISO 200). But actual exposure doesn't change -- the shot clips at exactly the same light level at all 3 settings. You're just darkening the image on the screen and cramming the range of available light values into a smaller area.

    This has been discussed many times.
    Last edited by jrd; 12-20-2016 at 01:00 PM.
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