Thread: ISO - Useless while shooting and in post

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  1. #31  
    Senior Member Karim D. Ghantous's Avatar
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    Rui, I'm glad you brought this up. I think we need to reacquaint ourselves with these kinds of fundamentals now and then. I take all this knowledge quite seriously, so it's good to be reminded to think about it.

    My take on RAW ISO: you have to set your light meter to something. ;-)

    It seems that, unlike stills cameras, RED RAW does not 'bake in' your ISO setting. It just records what hits the sensor, and that's it. ProRes is obviously a different thing.

    Mark, I look forward to watching your video.
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  2. #32  
    Senior Member Rui Guerra's Avatar
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    Quote Originally Posted by Karim D. Ghantous View Post
    Rui, I'm glad you brought this up. I think we need to reacquaint ourselves with these kinds of fundamentals now and then. I take all this knowledge quite seriously, so it's good to be reminded to think about it.
    Karim, I could not agree more that we all need to have a deep understanding of this and many other aspects of filming. That's why it is so important to have these kinds of "debates" and brainstorm. And no better place like this forum to do it.

    Quote Originally Posted by Karim D. Ghantous View Post
    Mark, I look forward to watching your video.
    Don't know if you saw the link, but here it is again: https://youtu.be/x1uAMYq7yQk
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  3. #33  
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    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).

    Changing ISO in-camera vs in-post yields the same brightness adjustment steps. However, the in-camera ISO setting, when used to help dictate your physical exposure on set, obviously *does* have an huge impact on the quality of your capture (and gives a better idea of how usable the image is). As mentioned, I'd argue that the WYSIWYG of an ISO applied image is more functional nowadays (more so in conjunction with the goal posts/stoplights as raw floor/clip guides).

    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. So either way, you're using an "ISO" like function/representation (sans normalization in the raw tools). The nomenclature - using ISO in fixed steps - is used merely because it's a known quantity/industry standard (or should've been... took RED until DSMC2 to recalibrate to a more meter friendly ISO scale).
    Last edited by Mike P.; 02-24-2021 at 11:06 AM.
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  4. #34  
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    CONT'D (for some reason, I'm getting an error msg when I try to post this all in the same post):

    What else? OH, Resolve defaults to 320 likely as a hold over from Mysterium, which was safely clean at that ISO (aka it's the lowest common denominator of all RED sensors), but it doesn't matter since you can change that setting to whatever you want as a default (in other words, it's moot).

    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).

    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.
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  5. #35  
    Senior Member Nick Morrison's Avatar
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    Quote Originally Posted by Mark A. Jaeger View Post
    Nick,
    I think we can all agree that camera capability is not infinite. As such, it is vital to adjust the physical exposure parameters, to the extent practical, to keep the image clear of stoplights and goal posts=sensor optimum. Setting ISO IMO in this case to something close to 800 is a good baseline. If you run out of range for the physical parameters my first choice is to add or subtract light. But, there are many situations where the light is not controllable. Then, say in very low lights, you need to use all the tricks (T1.5@1.5, LL OLPF, 360 shutter, etc) and this includes raising ISO even though this may expose the noise. It’s a balancing act.
    With respect to inciting the crew to light as needed I suggest skewing the display (ISO or monitor brightness) may not be the best managerial choice. Who’s the boss?
    Yes we set 800 as a baseline, but that's not set in stone. An Epic Dragon is noisy at 800 ISO, so we set it at 400 ISO. Also situations vary. If you are shooting Tungsten, you can sometimes get a noisier picture at 800 ISO. Some cameras do better if you ISO down with Tungsten (the blue channel can get starved when you have too much warm light). I say this from experience.

    And yes sometimes you get cleaner blacks if you rate down. Just having black in the frame doesn't mean it won't be noisy. It's horses for courses.

    In general not a fan of absolutes.
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  6. #36  
    Moderator Phil Holland's Avatar
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    Nick makes an interesting point regarding Color Temperature and Illuminant Source being an issue occasionally. This manifests squarely in how much apparent visual noise and even color stability when working under different color sources. Most modern digital sensors obviously work well within a general range of 2800-6500K, but you certainly see some photon starving sources that dip into 1800K or lower as well as above 6500K.

    This is actually why I have to first test how cameras work under both of the main hero temperatures used in this industry. Tungsten and Daylight.

    Very much pertaining to this conversation is my last RED Monstro and Arri Alexa test from 2019, I'm going to link to the ISO Ramps that showcase the differences in dynamic range, color stability, as well as apparent image noise for an equally exposed image:

    Timecode: 6:04
    https://youtu.be/XZPa3yp7lsQ?t=364

    This was done around the last time I had to test all the professional cameras targeting a 4K finish. i.e. RED, Arri, Sony, Canon top of the line bodies. The goal here was to understand deeply the strengths and weaknesses of each system, discover the yield and stop signs when it comes to a clean-ish out of camera image and when a noise reduction workflow would be needed when it comes to rating the ISO and exposure practices. We do some additional testing including custom tone maps, experiment with some look development, and a few other things. Eventually opening into testing a lot of colorful lighting conditions. Generally the footage from these tests get looked at for some time and it would be tricky to show every bit of information learned in an edited video online, but here I'm showing the most useful and practical information.
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    Red Dragon
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  7. #37  
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    Quote Originally Posted by Nick Morrison View Post
    Yes we set 800 as a baseline, but that's not set in stone. An Epic Dragon is noisy at 800 ISO, so we set it at 400 ISO. Also situations vary. If you are shooting Tungsten, you can sometimes get a noisier picture at 800 ISO. Some cameras do better if you ISO down with Tungsten (the blue channel can get starved when you have too much warm light). I say this from experience.
    But totally dependent on OLPF. Like LLO at 1600, is as clean as ISO400 of STH on Epic Dragon (especially after downscale to 4k). As it pertains to the OP's 'ISO relevance', this is a prime example of where, outside of the goalposts/stoplights, RED's raw tools aren't as effective (since they're locked at "ISO800" but the noise floor isn't a concern for another ISO stop or two).

    And, yeah, tungsten be starving the blues, which is also another prime example of where the raw tools wouldn't register it properly. I was under the impression that's why a lot of cinematographers don't change the temp in low-light tungsten shots (e.g. a lot of Soderberg's RED shot night scenes are left at 5000k regardless of the light source temp.)
    Last edited by Mike P.; 02-24-2021 at 06:36 PM.
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  8. #38  
    Senior Member Karim D. Ghantous's Avatar
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    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.
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  9. #39  
    Moderator Phil Holland'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.
    Depends on what you are trying to do. Back in the MX days we certainly used blue filters to assist with pulling keys off of green screen in particular, but these days, i.e. the last decade, that's been pretty much something that's not needed anymore.

    We're in a pretty colorful and vibrant world now given what the lights can do and how they are used. People often who shoot tungsten, daylight, and other things nearby are often tying it to the look they are going for and most often how it impacts the skin tones and subsequent surrounding colors you build upon.
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    Data Sheets and Notes:
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    Red Dragon
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  10. #40  
    Senior Member Simon Dunne's Avatar
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    If ISO is just metadata, then why do we need HDRx?

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