4K 30fps vs. 1080p 60fps

Discussion in 'Digital Video' started by JTfilmFX, Oct 2, 2016.

  1. JTfilmFX macrumors member

    JTfilmFX

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    #1
    Hey guys. Had a question about filming on the iPhone 7Plus. I love the look of videos shot in 1080p at 60fps.

    My question is this....

    When shooting video at night or in dark environments, which setting on the iPhone 7 plus captures more light and deeper, richer blacks? 1080p at 60fps... or... 4K at 30fps.
     
  2. Gwendolini macrumors 6502

    Gwendolini

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  3. Floris macrumors 68020

    Floris

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    #3
    1080p@60fps will get you the best result for poorly lit environments.
    Plus, you will have more frames to work with, great for after the fact slow motion.
     
  4. KeithPratt macrumors 6502a

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    Mar 6, 2007
    #4
    Shooting at 30fps means the shutter can go as low as 1/30 second, letting in twice as much light as shooting at 60fps with a lowest-possible shutter of 1/60 second.

    Shooting at 30fps, I doubt you'd get a better image with 1080p than you would 4K. 4K will probably show more noise, but with 1080p there will most probably be mushiness in its place.

    If you have the patience to run noise reduction when you come to edit (assuming you do come to edit), shooting 4K would certainly be better for image quality, but it might take a very long time to process.
     
  5. bent christian, Oct 3, 2016
    Last edited: Oct 3, 2016

    bent christian Suspended

    bent christian

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    #5
    General speaking, shutter speeds should be twice the frames per second. Of course, you can go lower than this when light is poor, but going down to 1:1 seems too low and will likely result in "smeared" frames when movement occurs.

    4k @ 30fps allows a lower shutter speed meaning more light and better exposure of each frame. 1080 @ 60fps will give sharper results to each frame, but will require more light or higher ISO (more noise) for the same exposure.

    https://vimeo.com/blog/post/frame-rate-vs-shutter-speed-setting-the-record-str
     
  6. RoobyRoobyRoo macrumors newbie

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    Oct 3, 2016
    #6
    My advice would be to shoot at 4K in 30 fps. The 30 fps allows the shutter to stay open longer and gather more light than 60 fps. After shooting, take the 4K video and downsample it to 1080. This will help reduce the inevitable noise and sharpen the image somewhat. You can shoot in 1080 and trust the phone to do this itself, and you'll probably get acceptable results, but personally I like to do those kinds of steps myself when I can to retain more control.
     
  7. KeithPratt macrumors 6502a

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    #7
    That's typical for movies, but not necessarily for other content. For live TV the temporal rate is typically sampled 60 times per second with the shutter set to 1/60th of a second (or 50 and 1/50th, depending on where in the world you are).

    Sampling at 1/30th of a second will give a smooth look, in many circumstances to the point of smeary, but whether it's better than the alternative noise penalty is a judgement call based on what and how you're filming, and is pretty difficult to give worthwhile general guidance for.
     
  8. bent christian Suspended

    bent christian

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    #8
    Sure, but we most likely aren't talking about live television here. The OP is using an iPhone to probably record home movies. Somewhere around FPS * 2 = Shutter Speed is where he should be. Take a risk and go lower if you like. At 4k, he can resample down to 1080 and remove a significant amount of noise.
     
  9. KeithPratt macrumors 6502a

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    #9
    Why should home movies have a half frame duration shutter speed? The OP says he likes the look of 60fps. That's probably a 1/60 shutter.
     
  10. bent christian Suspended

    bent christian

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    #10
    That is an assumption based on nothing.
     
  11. KeithPratt macrumors 6502a

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    #11
    That home movies should have a shutter duration half the frame rate or that the 60fps the OP speaks of is probably a 1/60th shutter?
     
  12. bent christian Suspended

    bent christian

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    #12
    For best results, shutter speeds should be twice the frames per second when recording video. This lower shutter speed (1/60 vs 1/120) and the greater number of pixels to resample (reducing noise) is why 4k @ 30fps is the correct answer.
     
  13. KeithPratt macrumors 6502a

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    #13
    I agree the answer to the original question is 4K 30fps, and this is possibly adding confusion, but can you qualify why you're insisting the shutter speed should be half the duration of the frame? A 1/60th shutter at 30fps is capturing the same motion blur in each frame as a 1/60th shutter at 60fps.
     
  14. scottrngr macrumors member

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    #14
    I'd shoot at 60fps at 1080. The shutter speed doesn't need to be 2x the frame rate. It's the frames per second that will give him the look he wants. However, the shutter speed needs to be in multiples. I.E. 60, 120, 180, 240 etc. The slower shutter speed will let more light in, and still give him the "live" look of 60fps. 30fps, even at 4k will still have that "film" look, although not as much as 24fps. Also, the files will be much bigger with 4k.
     
  15. handsome pete macrumors 68000

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    #15
    Are there 3rd party video apps that allow for changing the shutter speed manually? I'm not sure why the conversation evolved into that argument when the original question seemed to suggest choosing between the phone's regular presets.

    FWIW, there's nothing wrong with using an equal shutter/fps ratio. It's generally suggested to double it to avoid possible excessive motion blur, but you're certainly not bound to it if you happen to like the aesthetic.

    Having said that, you're probably going to get you best low light performance with 1080@30 versus 1080@60 and 4K@30. But if you have a chance, why don't you just do a simple test? Shoot a subject at all different settings and compare.
     
  16. bent christian Suspended

    bent christian

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    #16
    Yeah, its all about getting the look you want, and its what I suggested. My point is in knowing the rules before you break them. 2 * FPS is what is suggested and should be the starting point. I think its irresponsible to suggest a user who might not understand exposure, the affect a longer shutter speed with have on motion blur, etc., go with a lower speed as a place to begin.
     
  17. KeithPratt macrumors 6502a

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    #17
    Suggested by whom? For what purpose?

    There is no blanket rule stating you should shoot with a shutter duration of half the frame rate. Movies for the most part do that, but TV (news, sports, game shows, etc.) for the most part uses 60 fields (equivalent to frames) with 1/60 shutter. With home movies you'll most often find the shutter speed is used to regulate exposure — which brings us back to the OP...

    Do you think "irresponsible" is a bit over the top?
     
  18. diamond3 macrumors 6502a

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    #18

    There's a few things being said that needs to be clarified. I don't know everyone else's experience on the topic, but I will say that this is something I do everyday for a career.

    What I know and what the general recommendations from almost anyone i've talked to in this area would be the following:

    In low light, a higher fps (60p vs 30p/24p) is worse for noise because typical the ISO is the one being raised to get a shot.
    It is recommended to always shoot at 2x your fps. 60p = 1/120 or 30p = 1/60. Yes, you can go lower, but that's what is always suggested for an optional motion blur.
    Shooting in 4k and downsampling to 1080p will provide your best picture quality. Noise gets smaller when you downsample compared to the original 1080p signal.

    I've worked in TV broadcast for sports games, shot commercials for national television and always the recommendation is the follow the shutter speed rule above, also known as a shutter angle of 180º. Your iPhone has a fixed aperture lens, so in bright daylight, it compensates that by increasing the shutter speed to 1/5000 or higher sometimes. For TV and other projects, that's why ND filters become so useful. To keep the shutter speed at the right level in brighter environment.

    So in my experience, contradictory to some of the above information, that is the recommendation. Unless there is confusion with 60i in the past at 1/60, you have to remember that was interlaced footage which isn't the same as 60p.
     
  19. KeithPratt macrumors 6502a

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    #19
    For the discussion of the relationship between shutter angle and frame rate, it is.

    60 fields has the same motion cadence as 60 frames.

    A shutter of 1/60 is effectively the same for 60 fields as for 60 frames — in both cases 360°. (While 60i is nominally 30fps, you couldn’t set the shutter to 1/30th.)
     
  20. joema2 macrumors 65816

    joema2

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    #20
    There absolutely IS a blanket rule for this, and that's why it is universally called the "180 degree shutter RULE": https://luispower2013.wordpress.com/2013/03/12/the-180-degree-rule/

    That doesn't mean the rule cannot be broken, and it is commonly deviated from to achieve a specific artistic goal: https://daredreamermag.com/2010/11/07/the-180s-of-filmmaking-part-2-the-most-commonly-broken-rule/.

    However that does not imply there is no rule for this -- there is and it is widely known in cinematography.
     
  21. KeithPratt macrumors 6502a

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    #21
    If cinematography narrows it down to movies and episodic TV aping the movie look.

    For it to be a blanket rule it would have to apply to soap opera, tennis, news, games shows, wildlife documentary, VR, simulation video, music concert, CCTV, reality TV, home movies, etc.
     
  22. joema2 macrumors 65816

    joema2

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    #22
    Actually ATSC TV is broadcast in two common formats: 1080i at 29.97 frame/sec (59.94 fields per sec, interlaced), using 1/60th shutter speed in line with the 180 degree rule. NBC, CBS and many others use that format.

    The other common format used by ABC, Fox, and ESPN networks is 720p/60 (59.94 frames/sec, progressive). I believe the 720p broadcasters also use 1/60th sec, so you're right in that sense -- they don't stick with 2x the shutter speed in the 720p case, however they all use 1/60th which is about 2x the 29.97 fps rate.

    For this thread it may be a moot point since the question concerned an iPhone, and you can't control the video shutter speed to my knowledge.

    The question was which produces better low light results in an iPhone 7 Plus, 4k/30 or 1080p/60. I tested this on my iPhone 7 (non-plus) in measured 2 lux illumination which is very dim, also including 1080p/30 and 720p/30. I examined downloaded the video files and examined the luma waveform and histograms and transcoded all to 1080p to see if it produced any benefit from 4k downscaling.

    I really could not see much difference. The 4k/30 clip appeared to have a little more noise than the others (even after downscaling) but it was exposed slightly brighter for unknown reasons. This shows how even a simple test quickly becomes complicated.

    The next step would be to re-shoot and see if the camera could be tricked into more equal exposures and/or normalize them to the same luma level in post, which I don't have time to do.

    In short the iPhone 7 shoots remarkably good video in extremely low ambient lighting. I'd estimate it's about equal to recent-generation $1k consumer camcorders unless they are using a slow shutter low light mode. Based on the simple testing I did, I don't see a major difference in low-light capability between 4k/30 and 1080/60, although it would take more testing to be sure.
     
  23. calaverasgrande macrumors 65816

    calaverasgrande

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    #23
    the lower the shutter speed, the higher you can set your f stop.
    At 60fps the camera will automatically be opening up the iris more in order to grab more light. This also means the depth of field will be much shorter. So more of the image will be out of focus.
    At 30fps, all other things being equal, the sensor gets twice as much light per frame, so the iris does not need to be as wide. So more of the subject should be in focus.
     
  24. KeithPratt macrumors 6502a

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    #24
    29.97i is sampled (roughly) 60 times per second, so 1/60 shutter speed = 360° shutter angle.

    ...Which puts all this theory pedantry in its place.

    I think it may be possible in third-party apps.

    In the case of the iPhone 7, it's a fixed aperture, isn't it?
     

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