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  • Pocket 4K DNG request

    Could someone with a pocket 4k camera record some raw clips with the lens cap on at ISO 400, 800 and 1250 and share a few DNGs?

    I got my pocket 4k but I'm finding the sensor to be quite noisy and wanted to compare with some other cameras out there.

    Thanks!

  • #2
    The sensor is quite noisy at low ISO. Go to the high ISO mode (e.g. 1600, 3200) and you get less noise and better DR.
    My YouTube channel

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    • #3
      Originally posted by Samuel H View Post
      The sensor is quite noisy at low ISO. Go to the high ISO mode (e.g. 1600, 3200) and you get less noise and better DR.
      My tests haven't found that to be true at all.

      Low ISO



      High ISO



      In both cases I exposed to the right and as you can see there's more noise in the shadows at the higher ISO and some is present in the mid-tones.

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      • #4
        If possible, when shooting low key scenarios in raw like the above (interior exposing for exterior), use low ISO and give the sensor as much light as possible through aperture. Exposing the sensor like Myownfriend did above should always result in the cleaner, richer image (light must be enough to expose sensor to the middle/right).
        Last edited by stip; 11-16-2018, 03:05 AM.

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        • #5
          Originally posted by townio View Post
          Could someone with a pocket 4k camera record some raw clips with the lens cap on at ISO 400, 800 and 1250 and share a few DNGs?

          I got my pocket 4k but I'm finding the sensor to be quite noisy and wanted to compare with some other cameras out there.

          Thanks!
          When stating a problem, better never post an example for others to evaluate because that would be too simple.
          Anyway, my quick guess is you are feeding too little light to the sensor and are expecting it to see into the dark with low noise...

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          • #6
            Originally posted by Robert Niessner View Post
            Anyway, my quick guess is you are feeding too little light to the sensor and are expecting it to see into the dark with low noise...
            +1
            Exposing for raw is like exposing a film stock with a fixed sensitivity, most people coming from compressed codecs need to get accustomed using 'ISO' differently.

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            • #7
              my tests
              My YouTube channel

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              • #8
                Originally posted by Samuel H View Post
                The sensor is quite noisy at low ISO. Go to the high ISO mode (e.g. 1600, 3200) and you get less noise and better DR.
                Huh?

                Um.

                No.

                The least noise is at ISO400 and ISO1250. You can refer to BMD's chart regarding how dynamic range is distributed throughout the ISO range.
                Pocketluts: Purpose-built LUTs for the Blackmagic Design Pocket Cinema Camera 4K
                Pocketluts Store

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                • #9
                  Originally posted by Samuel H View Post
                  From my understanding, there's noise introduced at the photosite level and additional noise that comes from analog to digital conversion. When applying analog gain as the Pocket 4K is doing at it's higher ISO, it's amplifying the photosite's signal which clips highlights that were only near to clipping before and the shadows are cleaner because the sensor level noise might be increased but ADC's noise isn't. Essentially you're separating them out to some degree. Based on that understanding, I would expect to still see noise in the deepest shadows but with the sensor noise pushed more into the mid-tones. That seems to be what's happening in my test. Of course the high ISO's shadows are still noisier in my tests because I'm compensating for the gain by closing the aperture and starving the sensor of light(signal) and allowing the noise to take over more.

                  In other words, it seems kind of impossible that it would have more dynamic range at the high ISO. Someone with deeper knowledge of what's happening at the electrical level would be able to explain this all better than I did though.

                  Are you sure you're looking at your results correctly?

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                  • #10
                    Originally posted by stip View Post
                    +1
                    Exposing for raw is like exposing a film stock with a fixed sensitivity, most people coming from compressed codecs need to get accustomed using 'ISO' differently.
                    Since native ISO is 400 and 3200 on the P4K those are the cleanest, right? and speaking of exposing on the BMMCC I would always shoot RAW at 800 iso because no matter what the sensor is recording at 400 so that would always make me expose one stop over without thinking about it. How does this function in the P4K? I just got mine. Basically what I am saying is how does noise even factor in if you shoot raw? but how does the camera choose a native ISO? Or is the P4K just different? (I hope not)
                    Last edited by Logan Myers; 11-16-2018, 03:40 PM.

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                    • #11
                      Keep in mind that video cameras all apply noise reduction in camera prior to video encoding. Compressed video encoding reduces apparent noise by averaging blocks of pixels to the same value in deep shadows.
                      There is no noise reduction applied to raw images unless you do it in post. So frame comparisons between video cameras and raw files without noise reduction are not of much use.
                      Linear raw images provide far more sensor data to work with in grading, but that data resolves noise well too down to levels that would be crushed to black by compressed video encoding. How you deal with it is part of grading.

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                      • #12
                        Originally posted by Logan Myers View Post
                        Since native ISO is 400 and 3200 on the P4K those are the cleanest, right? and speaking of exposing on the BMMCC I would always shoot RAW at 800 iso because no matter what the sensor is recording at 400 so that would always make me expose one stop over without thinking about it. How does this function in the P4K? I just got mine. Basically what I am saying is how does noise even factor in if you shoot raw? but how does the camera choose a native ISO? Or is the P4K just different? (I hope not)
                        Yup! Exposing the for the Pocket Fourk works the same as other BMD cameras. When it comes to in-camera settings, you can set the ISO to whatever you want within each range since it's essentially like a pre-grade.

                        What I do is expose so that the zebras (set to 100) are either just starting to show or just before showing so that I'm giving the sensor as much light as possible. If the scenes dynamic range is low and the final image is suppose to be darker than what I'm seeing then I just lower the ISO to get a sense of what it would look like in post. Alternately, if I'm filming somebody who is indoors and standing by a window (and for whatever reason I don't have any lights or bounce to compensate), I'll up the ISO to maybe 1000 which will allow me to see more into the shadows and determine if I think I can clean up the shadows in post. If I can't then I'm obviously not gonna sacrifice the subject of the shot just to protect highlights so I'll start to clip highlights at the point.

                        Also I think you might have gotten your numbers backwards. The BMMCC's native ISO was 800 so exposing for middle grey at 400 would give you one stop more exposure :-)

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                        • #13
                          Originally posted by Logan Myers View Post
                          Since native ISO is 400 and 3200 on the P4K those are the cleanest, right? and speaking of exposing on the BMMCC I would always shoot RAW at 800 iso because no matter what the sensor is recording at 400 so that would always make me expose one stop over without thinking about it. How does this function in the P4K? I just got mine. Basically what I am saying is how does noise even factor in if you shoot raw? but how does the camera choose a native ISO? Or is the P4K just different? (I hope not)
                          Not quite. The high ISO mode starts at 1250. This is the cleanest "high" ISO.

                          "Native" ISO is, and always has been, a misnomer. What it almost always means is the ISO that yields the most dynamic range.

                          So, 3200 is definitely noisier than 1250 (it's essentially post-gain.)
                          Pocketluts: Purpose-built LUTs for the Blackmagic Design Pocket Cinema Camera 4K
                          Pocketluts Store

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                          • #14
                            Originally posted by Myownfriend View Post
                            What I do is expose so that the zebras (set to 100) are either just starting to show or just before showing so that I'm giving the sensor as much light as possible. If the scenes dynamic range is low and the final image is suppose to be darker than what I'm seeing then I just lower the ISO to get a sense of what it would look like in post. Alternately, if I'm filming somebody who is indoors and standing by a window (and for whatever reason I don't have any lights or bounce to compensate), I'll up the ISO to maybe 1000 which will allow me to see more into the shadows and determine if I think I can clean up the shadows in post. If I can't then I'm obviously not gonna sacrifice the subject of the shot just to protect highlights so I'll start to clip highlights at the point.
                            Let me suggest an alternate exposure method: (Not saying this one is wrong, just giving another option.)

                            Expose for your subject. Crazy idea, huh. ;-) I was so used to shooting ETTR on low DR 8-bit cameras that it took me awhile to trust the Pocket 4K, but now almost a month in, it's become second nature.

                            Seriously, if you're shooting RAW, there is enough latitude to just "get it right" in camera. Use false color to nail either middle grey (yet another reason to carry a grey card) or your subject's skin and roll. Not only is it intuitive, but it requires less work in post.
                            Pocketluts: Purpose-built LUTs for the Blackmagic Design Pocket Cinema Camera 4K
                            Pocketluts Store

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                            • #15
                              I really have no particular interest on trying to convince anyone here of anything. I shot a test, and found the high-ISO mode to have more DR and less noise than the low-ISO mode. There are plenty of technical reasons for something like this to be perfectly possible. Or maybe my p4k is different from every other p4k, so, shoot your own test and see how yours works. I posted the video and my thoughts about it because I though other people might be interested, but really, I did my test because *I* need to know how my camera works in order to get the most out of it (and given my results, that means I'm always going to shoot in the high-ISO mode and add more ND filtration). YMMV.
                              My YouTube channel

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