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  • ETTR and Middle Gray

    After searching and searching and searching, I have yet to find the discussion I'm looking for on ETTR and middle gray.

    Story time:

    I was at work for my day job, when a film crew set up to shoot a corporate video for my company. I was introduced to the director, and it just so happened that I had my BMCC with me. He was an incredibly gracious guy and asked if I could shoot some b-roll for him. I said sure.

    I was in an office environment with overhead fluorescents (not a huge range in exposure). To be on the safe side, I wanted to make sure I was saturating the sensor with enough light, so I ETTR by dialing down to just sliding under my zebras for what I deemed important (essentially everything except the bare bulbs in the office). Shot Prores.

    When I offloaded my footage at the end of the day, I told the director that the images look overexposed, but all he needed to do was bring down the exposure level and crank the saturation to get a good starting point for the image. When the DP saw the footage, he was baffled that I ETTR. He was unfamiliar with the BMCC, so I mentioned that this camera loves light, and this was the best way to ensure the blacks were clean. His response was "What about middle gray? The skin tones are the most important part of this shoot, and overexposed faces kill them." I also mentioned that from my tests and what I have researched, the "Film" mode of the BMCC is much more linear than logarithmic, so placing skin tones at a higher IRE wouldn't rob them of color. He said he didn't buy it.

    I understand the need for great skin tones and getting an exposure that is appropriate for the shoot, but am I wrong here? If you are going for more accurate skin tones, is there a sweet spot in terms of IRE to hit with the BMCC?

    After I essentially told him I felt middle gray wasn't as much of a concern due to the color science and response curve of this particular sensor, he called me "lazy", and that I "should have known better." To be fair to him, this was his set and I didn't even consult with him. I just asked one of the camera operators what focal lengths and apertures they were using to match the look they were going for and started my own 2nd unit. I essentially worked under the director, and in our scramble to get footage, I thoughtlessly didn't have a conversation with the DP before choosing my exposure technique. No wonder he wasn't impressed!

    The general rule (but not the gospel) for hitting the sweet spot in terms of dynamic range and cleaner SN ratio with the BMCC is ETTR just under clipping what is most important. My question is: what is the sweet spot for middle gray in terms of IRE to get the most color information?

    After my initial flop sweat, I decided to load Resolve, bring down the exposure, boost the saturation, and add just a little contrast. He thought the image looked great and softened his stance. I could tell he was coming from a place of trying to help me, not tear me down. Am I missing a lesson here? I just want to make sure I can communicate my process more clearly and verify the facts. When it comes to the most rich skin tones, where do you like to put them? I definitely learned a little set etiquette today, for sure!

    EDIT: Here's a test I performed to get to the bottom of all of this.



    Here are the DNGs: https://www.dropbox.com/s/t4meutfl6b...20Caldwell.zip

    Vimeo link is here: https://vimeo.com/87841148
    Last edited by Jared Caldwell; 02-28-2014, 01:29 AM.

  • #2
    For ProRes I don't think this is how you want to work. There's room to recover from the LOG (which actually isn't linear) but not that much, thus it's quite dangerous. I believe John said Middle Gray for the camera was around 40, but can't remember exactly.

    RAW or ProRes, if I do use a waveform (Which I have been) nothing goes over 60IRE, and skin rarely ever rises above 40-50.

    Once I stopped extreme ETTR and set into a +1.0 - -1.0 bracket, I've been able to get much nicer footage from the camera.

    Pick your poison.

    SKYPE (best way to talk to me): Camera_Kholi | twitter
    Avery and Pete: Superseeds Feature Film Trailer

    Comment


    • #3
      The camera with a proper exposure tool (an explicitly named "Exposure" dial) should handle exposure the way changing exposure on the camera itself changes the image, as we know from shooting with these cameras.

      That being said, they will need to know that this is the way BMCC footage works best and the way it produces the cleanest graded image. It may not be a widely used method of exposing a camera, but as we know and have tested, it works well on the BMD cameras.

      What camera(s) were they using on set? I've never shot a RED camera so I don't know if ETTR is also good practice. Any non-linear/logarithmic semi or fully baked image cannot be exposed to the right without consequences as "exposure" will not reduce or increase it in the correct fashion.

      Indeed, ETTR is a very digital, technical method of exposing a shot and is essentially exclusive to digital sensors capturing a "raw" image (untouched log or linear), so if the DoP has never done this before and the director has never seen it, it's not surprising it would be alarming to see.

      For the colourist, without an actual linear "exposure" adjustment tool, it's not as easy to work with ETTR footage, so that could also be a concern. Even in photography, there isn't a great deal of support for exposing to the right with raw files in stills. Often it's because we are simply not given the measurement tools (like a raw histogram or raw clipping alert) to photograph this way in DSLRs.

      Comment


      • #4
        Thanks for the response, Kholi. I was just quoting something from JB when he said he felt like the LOG curve is more linear in nature (maybe that is a misquote) and that he felt that placing your subject at a higher exposure didn't rob you of color information.

        Luckily, the footage still looked great, so no harm no foul really. I just want to make sure I'm understanding everything correctly and that I'm turning in footage that satisfies.

        When you say nothing goes over 60IRE, do you mean "nothing" or just what subjects you deem the focus of the shot?

        I looked at the posts where you described your shooting methodologies, Kholi. What problems were you having with extreme ETTR? Did you lose color information where you found it most important?

        Comment


        • #5
          Originally posted by Kholi View Post
          For ProRes I don't think this is how you want to work. There's room to recover from the LOG (which actually isn't linear) but not that much, thus it's quite dangerous. I believe John said Middle Gray for the camera was around 40, but can't remember exactly.

          RAW or ProRes, if I do use a waveform (Which I have been) nothing goes over 60IRE, and skin rarely ever rises above 40-50.

          Once I stopped extreme ETTR and set into a +1.0 - -1.0 bracket, I've been able to get much nicer footage from the camera.

          Pick your poison.
          Was it a noticeable change going back to only slight overexposure? I've found great results from ETTR in ProRes but it does require being careful with not allowing it to clip and using the right tool to underexpose (FilmConvert does a great job with its exposure slider in ProRes).

          Comment


          • #6
            Originally posted by nickjbedford View Post
            The camera with a proper exposure tool (an explicitly named "Exposure" dial) should handle exposure the way changing exposure on the camera itself changes the image, as we know from shooting with these cameras.

            That being said, they will need to know that this is the way BMCC footage works best and the way it produces the cleanest graded image. It may not be a widely used method of exposing a camera, but as we know and have tested, it works well on the BMD cameras.

            What camera(s) were they using on set? I've never shot a RED camera so I don't know if ETTR is also good practice. Any non-linear/logarithmic semi or fully baked image cannot be exposed to the right without consequences as "exposure" will not reduce or increase it in the correct fashion.

            Indeed, ETTR is a very digital, technical method of exposing a shot and is essentially exclusive to digital sensors capturing a "raw" image (untouched log or linear), so if the DoP has never done this before and the director has never seen it, it's not surprising it would be alarming to see.

            For the colourist, without an actual linear "exposure" adjustment tool, it's not as easy to work with ETTR footage, so that could also be a concern. Even in photography, there isn't a great deal of support for exposing to the right with raw files in stills. Often it's because we are simply not given the measurement tools (like a raw histogram or raw clipping alert) to photograph this way in DSLRs.
            Cameras were Sony F55 and Sony F3.

            I understand that ETTR is typically a RAW technique, but with careful consideration to the highlights, I found the technique works for Prores due to the 10-bit color space. You still have a lot of information to play with.

            Comment


            • #7
              Originally posted by nickjbedford View Post
              The camera with a proper exposure tool (an explicitly named "Exposure" dial) should handle exposure the way changing exposure on the camera itself changes the image, as we know from shooting with these cameras.

              That being said, they will need to know that this is the way BMCC footage works best and the way it produces the cleanest graded image. It may not be a widely used method of exposing a camera, but as we know and have tested, it works well on the BMD cameras.

              What camera(s) were they using on set? I've never shot a RED camera so I don't know if ETTR is also good practice. Any non-linear/logarithmic semi or fully baked image cannot be exposed to the right without consequences as "exposure" will not reduce or increase it in the correct fashion.

              Indeed, ETTR is a very digital, technical method of exposing a shot and is essentially exclusive to digital sensors capturing a "raw" image (untouched log or linear), so if the DoP has never done this before and the director has never seen it, it's not surprising it would be alarming to see.

              For the colourist, without an actual linear "exposure" adjustment tool, it's not as easy to work with ETTR footage, so that could also be a concern. Even in photography, there isn't a great deal of support for exposing to the right with raw files in stills. Often it's because we are simply not given the measurement tools (like a raw histogram or raw clipping alert) to photograph this way in DSLRs.

              RED suggest ETTR with Dragon, as far as MX or EPIC goes you definitely do not want to go too far to the right, as I don't think it's truly linear. In my early days I tried doing that and completely killed a shot. RED's a lot better as far as noise floor goes than it is with highs. Still, if you go too far to the left you also damage color.

              Ideally, you just nail it shooting with that camera and know you have some leeway on either side.

              Originally posted by Jared Caldwell View Post
              Thanks for the response. I was just quoting something from JB when he said he felt like the LOG curve is more linear in nature (maybe that is a misquote) and that he felt that placing your subject at a higher exposure didn't rob you of color information.

              Luckily, the footage still looked great, so no harm no foul really. I just want to make sure I'm understanding everything correctly and that I'm turning in footage that satisfies.

              When you say nothing goes over 60IRE, do you mean "nothing" or just what subjects you deem the focus of the shot?

              I looked at the posts where you described your shooting methodologies, Kholi. What problems were you having with extreme ETTR? Did you lose color information where you found it most important?

              Sorry, I should have clarified: anything important, really. Landscapes etc. I don't see a major issue with ETTR, still approaching with caution by using zebras set to about 85%. I say that because of the camera's zebras not actually telling you when a single channel is clipped.

              Extreme ETTR produced a fair amount of inconsistencies that were excruciating to balance in post, most related to color. I know for sure that part of it's due to the Tiffen filters (moved on to Hoyas now), some of it channels clipping because I relied on the 100 percent zebras too much, and the overall fact that you really don't want to jump all over the place with exposure just to avoid noise.

              Noise also has its own part to play on the image, not just in texture but color.

              Just some thoughts. I've never seen/read a clear answer on Middle Gray for the camera, but it does seem to be somewhere in that range -- or even lower which would be frightening.

              SKYPE (best way to talk to me): Camera_Kholi | twitter
              Avery and Pete: Superseeds Feature Film Trailer

              Comment


              • #8
                Originally posted by Jared Caldwell View Post
                Cameras were Sony F55 and Sony F3.

                I understand that ETTR is typically a RAW technique, but with careful consideration to the highlights, I found the technique works for Prores due to the 10-bit color space. You still have a lot of information to play with.
                Yeah I only shoot ProRes and also do ETTR on it and I find I still get exactly the image I want after pulling it down.

                It appears that FilmConvert and Nick Shaw's LUT plugin etc do proper linear exposure adjustment (like raw converters), which is how it needs to be done, then the LUT is applied to the adjusted image.

                Comment


                • #9
                  Originally posted by Kholi View Post
                  RED suggest ETTR with Dragon, as far as MX or EPIC goes you definitely do not want to go too far to the right, as I don't think it's truly linear. In my early days I tried doing that and completely killed a shot. RED's a lot better as far as noise floor goes than it is with highs. Still, if you go too far to the left you also damage color.

                  Ideally, you just nail it shooting with that camera and know you have some leeway on either side.
                  That sounds like what I thought. With a RED camera, you are photographing like you are photographing with a stills camera. You've got the resolution and supersampling to handle noise and exposure essentially should be within a half a stop or so and you'll have nice headroom on either side like raw photographs.

                  I think the reason for doing ETTR on the BMCC and Pocket cameras is that they don't have the high resolution to counter the noise floor (which is quite acceptable anyway) so crushing the noise floor in post helps.

                  Comment


                  • #10
                    Originally posted by Kholi View Post
                    Sorry, I should have clarified: anything important, really. Landscapes etc. I don't see a major issue with ETTR, still approaching with caution by using zebras set to about 85%. I say that because of the camera's zebras not actually telling you when a single channel is clipped.

                    Extreme ETTR produced a fair amount of inconsistencies that were excruciating to balance in post, most related to color. I know for sure that part of it's due to the Tiffen filters (moved on to Hoyas now), some of it channels clipping because I relied on the 100 percent zebras too much, and the overall fact that you really don't want to jump all over the place with exposure just to avoid noise.

                    Noise also has its own part to play on the image, not just in texture but color.

                    Just some thoughts. I've never seen/read a clear answer on Middle Gray for the camera, but it does seem to be somewhere in that range -- or even lower which would be frightening.
                    Thanks for sharing. Everyone has different methodologies, and I understand where you're coming from in terms of clipping a color channel. I guess I'm just trying to find a better answer for DPs than "middle gray?" There are a few go-to "sweet spots" for the BMCC in terms of overall exposure, it'd be nice to know how to advise on a middle gray sweet spot for the BMCC.

                    Comment


                    • #11
                      http://provideocoalition.com/aadams/...ure-sweet-spot

                      http://provideocoalition.com/aadams/..._you_use_it/P2

                      -- That may help, may not

                      I distinctly remember reading that it was close to Alexa, and Alexa's supposed to be around 40-50. I think it's safe, but would definitely like to hear from others.

                      SKYPE (best way to talk to me): Camera_Kholi | twitter
                      Avery and Pete: Superseeds Feature Film Trailer

                      Comment


                      • #12
                        I'm just learning how to get the most out of my SmallHD DP4 HML (high, medium, low) false color tool. I really like that the middle IRE range of 50-58 stands out as orange. That's where I thought I would normally expose skin. I need to experiment with darker and lighter skin tones to figure out how much skin to place in the range below or above, though I'm hoping I can just expose darker tones with just a little orange showing and palest skin with mostly orange. At least this is how I had planned to use the HML tool in normal lighting, like an interview.

                        Now Kholi says he exposes all skin quite a bit darker, and nothing (!) over 60. Can you elaborate?

                        Any other thoughts? For myself I'm really talking about ProRes log/film here, not raw.

                        This article provided some framework for me, though no definitive answers: http://www.ryanewalters.com/Blog/blo...83675371023276

                        Comment


                        • #13
                          Thanks for posting those. I remember finding the links on another thread. I feel bad if this is duplicate information, but I am interested in understanding middle gray on the BMCC. It seems like it hasn't gotten the same amount of attention as other aspects of exposure for the camera.

                          Comment


                          • #14
                            Originally posted by Steve Wake View Post

                            Now Kholi says he exposes all skin quite a bit darker, and nothing (!) over 60. Can you elaborate?
                            [/url]
                            I try not to let skin roam over 60, and for me it's been pretty consistent and has turned out the most pleasant images from the camera since I've started using it. If it's just an exterior or something similar, wide, then it's okay to grab more light.

                            It really is up to you guys how you use it, extreme ETTR hasn't been a very solid way to work for me.

                            Jared - PM John Brawley if you want a definitive answer, I don't think anyone else actually knows it which is why you can't find the info. I tend to agree with the posters/responses on Art Adams' Alexa post, Waveforms + LOG kind of don't make sense but we don't have much else.

                            SKYPE (best way to talk to me): Camera_Kholi | twitter
                            Avery and Pete: Superseeds Feature Film Trailer

                            Comment


                            • #15
                              "... I understand where you're coming from in terms of clipping a color channel …"

                              I understand the term"color channel" with 3-chip cameras because there are 3 data channels, but in a single-chip camera I'm wondering what it means since in raw mode the data stream from the sensor is a color sequence.

                              In ProRes mode, after deBayering there would, of course, 3 channels.

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