Thread: Blackmagic Pocket 4K, best Iso's for Dynamic Range and Noise

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  1. #21  
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    Quote Originally Posted by CaptainHook View Post
    ISO1600 is the same log curve as ISO160, just with analog gain applied on the sensor.

    Also while generally it is true that with RAW ISO is just metadata, you have to be careful as on the Pocket 4K analog gain is used and you can't change that after the fact. You can't shoot ISO400 and then change to ISO3200 and have it look the same as if you shot ISO3200 in camera for example. So the ISOs available in RAW are limited to the valid list for the analog gain that was used at the time of shooting.
    Thanks Hook for tuning in.
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  2. #22  
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    Quote Originally Posted by CaptainHook View Post
    ISO1600 is the same log curve as ISO160, just with analog gain applied on the sensor.

    Also while generally it is true that with RAW ISO is just metadata, you have to be careful as on the Pocket 4K analog gain is used and you can't change that after the fact. You can't shoot ISO400 and then change to ISO3200 and have it look the same as if you shot ISO3200 in camera for example. So the ISOs available in RAW are limited to the valid list for the analog gain that was used at the time of shooting.
    Can you address ProAV's test and what happened with ProRes at ISO 1600? I've verified the same behavior...it's demonstrably worse than RAW, and worse than should be expected from the surrounding ISOs.
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  3. #23  
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    i Would think the low native base ISO would give the best performance.
    Cheers
    Last edited by Denny Smith; 12-05-2018 at 01:57 AM.
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  4. #24  
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    Quote Originally Posted by Denny Smith View Post
    Actually i think ISO 1600 has no analog gain added, you are in the low res Ge of the dual sensor, and ISO 1600is underexposed by two stops. So you are,going to get more noise. Jump up to the high base ISO and you will get better results.
    Cheers
    No, the high gain circuit cuts in at ISO 1250. But the problem with ISO 1600 ProRes isn't with noise, it's how poorly it handles overexposure.
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  5. #25  
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    Quote Originally Posted by joe12south View Post
    Can you address ProAV's test and what happened with ProRes at ISO 1600? I've verified the same behavior...it's demonstrably worse than RAW, and worse than should be expected from the surrounding ISOs.
    There is nothing to address with ProAV's test, because Karl did make wrong assumptions how things are working. He was using ISO steps for testing dynamic range, which should never be done. You have to adjust the light level for proper tests. And he did no realize that going from ISO 800 to ISO 1600 brought him into the second gain stage, where dynamic range is reduced compared to the first gain stage.
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  6. #26  
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    Quote Originally Posted by Robert Niessner View Post
    There is nothing to address with ProAV's test, because Karl did make wrong assumptions how things are working. He was using ISO steps for testing dynamic range, which should never be done. You have to adjust the light level for proper tests. And he did no realize that going from ISO 800 to ISO 1600 brought him into the second gain stage, where dynamic range is reduced compared to the first gain stage.
    I understand all of that, but even still, he stumbled onto some weirdness: ProRes ISO 1600 performance is anomalous. You can test this for yourself. You can go up or down just one step and get demonstrably better performance.
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  7. #27  
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    Better performance at what?
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  8. #28  
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    Quote Originally Posted by jrd View Post
    I would guess you could get as much detail out of 3200 (in post) as you would shooting 25600 (at the same exposure in both cases), despite the fact that 25600 footage will be much brighter straight of the camera.
    Not quite which is what I was trying to explain. Beyond ISO6400 there is more analog gain applied at each ISO which is why total dynamic range reduces. At ISO3200 you have around 12.3 stops, at ISO25,600 you have around 10.7. In RAW if you shoot ISO3200 we do not allow setting ISO25,600 because the analog gain and noise performance/clipping point is different so changing it in post would not match setting it that way in camera.

    Quote Originally Posted by joe12south View Post
    Can you address ProAV's test and what happened with ProRes at ISO 1600? I've verified the same behavior...it's demonstrably worse than RAW, and worse than should be expected from the surrounding ISOs.
    Its because of what I described. At ISO1600 you are using analog gain so the image will clip faster as you are boosting it before the ADC. You also drop in total DR from around 13.1 stops to around 12.3. In RAW you might be able to recover a little more highlights with highlight recovery from non-clipped channels compared to ProRes but that will depend on the scene white point and your colour temp settings. ISO160/1600 would have the same amount of stops over middle grey (around 4) but ISO160 will take more light on the sensor before it clips than ISO1600 if you don't adjust how much light is gathered by the sensor going between the two. All things the same it will clip faster on the higher analog gain settings.

    I believe they did a follow video explaining that using ISO to adjust exposure was not doing what they thought it did. You really want to change either aperture or integration time (shutter and/or frame rate) for what they were trying to do.
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  9. #29  
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    Quote Originally Posted by joe12south View Post
    ProRes ISO 1600 performance is anomalous. You can test this for yourself. You can go up or down just one step and get demonstrably better performance.
    Can you post some examples? ISO1250 should have around 3.8 stops over mid grey and ISO1600 around 4.1. I'd expect them to look fairly similar.
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  10. #30  
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    I have just tested it on my PCC4K and found no anomalies between ISO1250, ISO1600 and ISO2000. It works as expected. So I am curious what Joe has to show.
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