Thread: ISO - Useless while shooting and in post

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  1. #41  
    Senior Member Mark A. Jaeger's Avatar
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    Simon,
    HDRx does not involve ISO. HDRx achieves the extra range by adjusting shutter speed. Two tracks are recorded simultaneously. If you shoot 1/48th shutter @ 24 fps you can add 1 stop of HDRx and the exposure for the X track will use 1/96 shutter. The A track will be captured at 1/48th as you set it.
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  2. #42  
    Senior Member Nick Morrison's Avatar
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    Quote Originally Posted by Karim D. Ghantous View Post
    If you are using tungsten lights with a digital sensor, are you not better off by using a filter? That way, you subtract the appropriate amount from your nominal ISO (the distance between daylight and tungsten, I believe, is 2/3 stop?). So your chosen grey point is exactly the same.
    Yes but sometimes you just want to use Tungsten lights. They have perfect IRE (100). They look amazing on skin. Or you're using Lekos, old school Lekos, and they're Tungsten. You can gel them sure, but you're also killing the output. So sometimes you just embrace them. But they are very warm, so you really have to watch the blue channel.
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  3. #43  
    Senior Member Rui Guerra's Avatar
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    Quote Originally Posted by Mike P. View Post
    This is one of those things that, on paper, seems like it should work fine, but in practice falls apart/isn't realistic. Ironically, RED's are weaker at this than others because their over/under is low-end weighted at 800ISO (which is what the raw tools/meters are based off of). It also makes ETTR somewhat less effective too; you're better off setting the ISO higher, and keeping exposure balanced (rather than ETTR), as it'll be more accurate and easier to finely tune based off of WYSIWYG (which ETTR does *not* do well, especially in log).
    Can you clarify a bit more what you mean? ETTR as always the benefit of providing more light to the sensor, which translates in more stops of light (DR) recorded, no matter the ISO value, right? Why your advice to set the ISO higher and not leave it and ETTR? (Although I agree that WYSIWYG is easier and helpful, potentially leading you to make better choices on set regarding lighting, aperture, ND or shutter angle.)


    Quote Originally Posted by Mike P. View Post
    End of the day if you think exposing using a Log image with just the raw exposure tools is less dangerous than using an ISO with gamma/colourspace (and/or LUT) applied reference image, you're welcome to shoot that way! But you'll inevitably run into unforeseen/unexpected problems, where important image info is too deep in the noise-floor and/or too hot to be recovered accurately (more likely). I think this is exactly what was happening with CineD's recent Komodo DR test; they did what you're thinking -- expose via log using ISO independent metering -- but because of RED's low-end weighted DR distribution it caused their skin tones to be an unrecoverable clip at only +1 from their base exposure (by comparison the p6k was +4, even though it has less DR).
    But if one uses a RAW image as reference in monitor and control exposure levels by making good use of GIOSCOPES, how can we make the error of loosing information in the shadows or clipped highlights?


    Quote Originally Posted by Mike P. View Post
    More practically, when using log/raw tools, you can't accurately see unwanted distractions on screen because the log is so flat there's hardly any differentiation by colour/brightness. Similarly, you'll have a difficult time trying to convince clients/producers at video village that your Log/GioScope image is "captured correctly"... but I digress.
    This two arguments, each on their own level of relevance, are indeed completely valid arguments. Could not agree more.
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  4. #44  
    Quote Originally Posted by Mike P. View Post
    Again, all REDs raw exposure tools use "ISO800" as their base (which is brighter than the native "brightness" of the sensor) and is already being converted/mapped from linear.)
    Hello Mike,

    could you expand on this ? which raw exposure tools are affected by this ?

    And are all RED camera raw tools since Red One based on ISO800 or was this changed with DSMC 2 ?

    Is there an official link to documentation that confirms this ?

    I was under the impression that the raw exposure tools like goal posts indicate clipping/crushing at the sensor level, independent of any ISO setting.

    Thanks.

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  5. #45  
    Moderator Phil Holland's Avatar
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    Quote Originally Posted by Allen Deckard View Post
    And are all RED camera raw tools since Red One based on ISO800 or was this changed with DSMC 2 ?
    GIOSCOPE, the RAW Meters/Goal Posts, as well as the Stop Lights all correctly read the RAW data.

    Exposure Check and Video Check take into account the gamma curve.
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  6. #46  
    Quote Originally Posted by Phil Holland View Post
    GIOSCOPE, the RAW Meters/Goal Posts, as well as the Stop Lights all correctly read the RAW data.

    Exposure Check and Video Check take into account the gamma curve.
    and where does the ISO800 come into play that Mike referred to ?

    Thanks.

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  7. #47  
    Senior Member Rui Guerra's Avatar
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    Quote Originally Posted by Phil Holland View Post
    GIOSCOPE, the RAW Meters/Goal Posts, as well as the Stop Lights all correctly read the RAW data.

    Exposure Check and Video Check take into account the gamma curve.
    Exposure Check is a mix. Based on RAW data at the low and high extremes (purple, red). The middle one (green) is indeed based on IRE values.

    From RED Dragon Manual:

    "The Exposure meter colors indicate the following information:

    Purple: Underexposed; indicates sensor exposure levels that may be noisy if gained up in post production.
    Green: IRE 41–48; based on the RGB levels of the video out signal and not the RAW data.
    Red: Overexposed; indicates sensor exposure levels that are clipping.
    Purple (underexposure) and red (overexposure) are based on RAW data and show areas that are clipping or close to
    clipping. The RGB settings DO NOT affect the Exposure indicators."
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  8. #48  
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    Quote Originally Posted by Allen Deckard View Post
    could you expand on this ? which raw exposure tools are affected by this ?
    And are all RED camera raw tools since Red One based on ISO800 or was this changed with DSMC 2 ?
    Is there an official link to documentation that confirms this ?
    I was under the impression that the raw exposure tools like goal posts indicate clipping/crushing at the sensor level, independent of any ISO setting.
    All the raw tools are "affected"; Graeme and/or Jarred have mentioned raw tools use an ISO800/RLF based image for their "raw representation".... That's up to at least DSMC1 Dragon (I'm not sure if DSMC2/ISOCal2 or Komodo are different... it doesn't need to change, RED just needs to promote Chip 10 being mid-grey, not Chip11). That said, because the clipping points/stop lights are the absolute ends, they technically wouldn't need a mapped reference, but Raw Exposure Check and GioScope use 800/RLF for their visual representation on the monitor for the stops in between.

    Quote Originally Posted by Rui Guerra View Post
    Can you clarify a bit more what you mean? ETTR as always the benefit of providing more light to the sensor, which translates in more stops of light (DR) recorded, no matter the ISO value, right? Why your advice to set the ISO higher and not leave it and ETTR? (Although I agree that WYSIWYG is easier and helpful, potentially leading you to make better choices on set regarding lighting, aperture, ND or shutter angle.)
    When you ride the high-side by ETTR, the closer you get to clip the less useful/saturated the information/colour is up there in the extreme high stops that you'd recover when you bring it down in post... Particularly true with RED because of their low-end weighted DR distribution and how their highlight recovery can register as not-clipped even though those stops may not be useful for anything other than monochrome/roll-off (again, like the CineD Komodo test).

    You're kind of answering your own question with the last line in brackets. It's why I started by saying on paper it makes sense, but in actuality it's easier/faster/more accurate to use an ISO applied reference to maximize the usable image (aka 'WYSIWYG is easier, helpful, potentially leading you to make better choices on set regarding lighting, aperture, ND or shutter angle.').

    Quote Originally Posted by Rui Guerra View Post
    But if one uses a RAW image as reference in monitor and control exposure levels by making good use of GIOSCOPES, how can we make the error of loosing information in the shadows or clipped highlights?
    Because it's simple to avoid the clip point and the noise floor, but where your low-mids and high-mids sit *before* the clip/floor is easier to navigate by having a WYSIWYG reference image (generally speaking). When you look at Chips 1~4 in GioScope, you can't really see how noisy they are (particularly in the blue channel under tungsten, for example). Similarly (and more likely), Chips 14~16 start lacking accurate colour, but you can't see that in Gio.

    It's easy to test! Turn GioScope on, set the high side of a face to chip 14 or 15 (which is ETTR ~2stops, and "not clipped") and then see how it looks when you recover it in post. 14 might look okay... 15 probably won't look like a good skintone (even though it's "only" chip 15 not clipped/16). Further, because the distribution is imbalanced, sometimes the mids that you ETTRed (which should be solidly captured) will lose contrast if you try to redistribute the DR to keep the skintone at a proper IRE value (hence why I don't recommend ETTR with RED, but adjusting ISO instead). When you use an ISO reference image you can see it in real-time so you're way less likely to over stretch/push it too far, even in a dynamic scene.

    In layman's terms, extreme high-end can get too questionable for ETTR (on a non-normalized reference image ala raw exposure check/gioscope), whereas a WYSIWYG/ISO image will, at the very least, look as it did on the set. Conversely, shooting at a *lower* ISO (but leaving the histogram even) is essentially the same as ETTRing in raw, but everyone on set will be seeing how it actually looks normalized, without question (which, imo, is "safer").
    Last edited by Mike P.; 03-13-2021 at 10:15 AM.
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  9. #49  
    Senior Member Adrian Jebef's Avatar
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    Quote Originally Posted by Mike P. View Post
    Because it's simple to avoid the clip point and the noise floor, but where your low-mids and high-mids sit *before* the clip/floor is easier to navigate by having a WYSIWYG reference image (generally speaking). When you look at Chips 1~4 in GioScope, you can't really see how noisy they are (particularly in the blue channel under tungsten, for example). Similarly (and more likely), Chips 14~16 start lacking accurate colour, but you can't see that in Gio.

    It's easy to test! Turn GioScope on, set the high side of a face to chip 14 or 15 (which is ETTR ~2stops, and "not clipped") and then see how it looks when you recover it in post. 14 might look okay... 15 probably won't look like a good skintone (even though it's "only" chip 15 not clipped/16). Further, because the distribution is imbalanced, sometimes the mids that you ETTRed (which should be solidly captured) will lose contrast if you try to redistribute the DR to keep the skintone at a proper IRE value (hence why I don't recommend ETTR with RED, but adjusting ISO instead). When you use an ISO reference image you can see it in real-time so you're way less likely to over stretch/push it too far, even in a dynamic scene.

    In layman's terms, extreme high-end can get too questionable for ETTR (on a non-normalized reference image ala raw exposure check/gioscope), whereas a WYSIWYG/ISO image will, at the very least, look as it did on the set. Conversely, shooting at a *lower* ISO (but leaving the histogram even) is essentially the same as ETTRing in raw, but everyone on set will be seeing how it actually looks normalized, without question (which, imo, is "safer").



    So I really agree with these observations. And I would say you really need a lot of experience shooting with the RED system to understand the intricacy of what Mike is talking about. I view each camera system as it's own thing. Although the basic technology is similar, how each camera gets to an image is different and can produce varying results. I've always viewed RED cams as looking their best with strong, sharp contrast (harder gamma curve). Their weak points have always been noisy shadows and harsh highlights. As much as these cameras can capture wide dynamic range the top and bottom will always be strongly crushed in the final image. As Mike says, putting too much important info (like an actor's face) in the top or bottom of the exposure range can leave you with questionable fidelity once you're in the grading stage.

    For me onset, and especially shooting with RED, I like to use a strong LUT that scales the recorded image properly so I can tell when over or under exposure starts to be problematic.
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  10. #50  
    Senior Member Rui Guerra's Avatar
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    Regarding best practices in post, what is the consensus here, regarding:

    1 - Anyone finds any advantage in going first to RedCineX and adjusting some RAW parameters before importing the footage to DaVinci Resolve?

    2 - Most importantly, once the footage is imported inside DaVinci Resolve, how important is to first change RAW parameters (in the Camera RAW tab) and then using the usual color grading tools of Resolve? Assuming that we start straight with Resolve, with the standard flat/log look of REDWideGamutRGB/Log3G10, should we rely entirely on the power of Resolve to give the best possible image quality just using color wells and it's other native color grading tools? Or is there any real advantage in going first to the Camera RAW tab of color grading page and do some prior adjusting of some Raw parameters (ISO, WB, etc) in a clip basis before start grading using Resolve's own tools?
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