gx7, 24p is better than 50p image quality wise?

Discussion in 'Panasonic Cameras' started by weee, Dec 29, 2013.

  1. weee

    weee Mu-43 Rookie

    Oct 2, 2013
    I dont know much about it but I've heard, due to some super sampling (I dont even know the exact term) algorithm, for a single frame, 24p is better than 50/60p? (although as a gx7 user, I personally can't really tell the differences)
  2. RuffDraft

    RuffDraft Mu-43 Regular

    Jan 13, 2013
    Are you talking about the basics behind 24p? If so, I know what you mean and can explain as far as I can understand:

    24p is the rate at which films are recorded. It gives you film-like footage, rather than screaming 'Home movies!" The best example so far of the differences in cinema has been The Hobbit, which was recroded at 48p, rather than 24p. A lot of people came out the cinema saying that it made them feel dizzy. Apparently our eyes have become accustomed to 24p, which is a reason why we prefer it too. But as far as I can understand, 50p and 60p also create a more sped-up reel, and therefore is optimal if you're wanting to do slow-mo in post.

    If you're talking about algorithms in a more professional way though, then I'm all ears to those on M43 board who know more than I do, as I'm just starting out too.
  3. stenlius

    stenlius Mu-43 Regular

    May 9, 2013
    It's the opposite - on the GX7 the best quality is achieved shooting 1080@50/60p depending on your camera's region. 1080p24 uses the Main profile of the AVCHD codec, and 50/60p uses the High profile, which is superior with it's dynamic switching the pixel blocks during compression. This kind of prioritizes areas with fine detail, which are given more data rate over the ones with low detail, which are given a lower bitrate. This concerns only the quality and not the cinematic feel of the video of course.
  4. val

    val Mu-43 Top Veteran

    Dec 19, 2013
    Real Name:
    Thank you for such a great post, I got one last question, in my mind 21mbps being 24fps and 28 being 50fps, shouldn't the mbps be even higher since it's recording twice the framerate?
  5. Levster

    Levster Mu-43 Top Veteran

    I was wondering about this too. It might be due to the way the Codec works. A lot of the newer Codecs start with a key frame and then describe the differences between this key frame and the subsequent frames. This takes advantage of the fact that there doesn't tend to be much of a difference between one frame and another, so with 50fps the difference between each frame would be even smaller than the difference between a 25fps frame, hence the data rate doesn't double. If you do any encoding using Handbrake you can actually set how often the key frame is captured, I think by default it uses 75. On top of that the information is compressed, just like a JPEG image. You can see where this codec fails when there is lots of movement and the codec isn't able to fully describe the change between each frame and the next. Luckily Panasonic's implementation is very good and it can cope with most scenes, whereas the Olympus implementation of the Codecs falls to pieces quite easily.
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  6. stenlius

    stenlius Mu-43 Regular

    May 9, 2013
    Nope, as I said at 50 fps the bitrate is utilized more efficiently due to the High profile compression, and the 28 Mbps is the standard bitrate that guarantees seamless playback on various platforms, supporting the AVCHD codec v2.0 - bluray players, camcorders, digital cameras, etc. There is a optimal point considering the quality/storage space needed, and I suppose that's why the 28 Mbps was included in the specs for the codec. Levster said the rest.

    Happy New Year and wish you all the best!!!
  7. lenshoarder

    lenshoarder Mu-43 All-Pro

    Nov 7, 2010
    I wouldn't say the newer video codecs do this, I would say pretty much all codecs do this. This is how compressed video has worked since the beginning. The only widely used standard that didn't was MJPEG. As the name implies, MJPEG is simply a stream of JPEGs. It's not really video compression.

    There are actually P frames and B frames. P frames are unidirectional as you are describing. B frames are bidirectional. A GOP size of 75 is a bit lean. 15-30 is more common. The bigger the GOP, the more the compression and the lower the bitrate. That's probably why Handbrake defaults to such a large GOP size. It's geared toward small screens and low bitrates.
  8. weee

    weee Mu-43 Rookie

    Oct 2, 2013
    what I meant was the technology to combine multiple pixels into one 'super' pixel, so the camera captures a much higher resolution for a single frame then downsizes it to normal HD resolution, if I make it clear; so for such technology, is it true it only works for 24p not 50/60p? it doesn't work in 50/60p because that would take too much bitrate to process? i could be wrong with the whole thing though because it doesn't seem to mention anywhere regarding this.