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420, 422, 444, rescaling and colors flame
  • 114 Replies sorted by
  • caveportcaveport

    @Vitaliy I think the buckets analogy is flawed. I suppose the topic title does contain the word 'flame' so I should not expect too much. Sorry for wasting everyone's time.

  • Vitaliy_KiselevVitaliy_Kiselev

    I think the buckets analogy is flawed. I suppose the topic title does contain the word 'flame' so I should not expect too much.

    Cool argument. :-) It is not flawed, as it is made to explain basic things.

  • MistasMistas

    @caveport, I don't have any allegiance to VK or anyone else...but I don't think he is saying that 2k10bit is an accurate representation of the source 4k8bit footage; all I see is simply that mathematically it really is 10bits of data coming from an 8bit down-sample.

    That does not mean it solves the limitations of banding, loss of color info, or any of the other side effects of the source 8bit signal.

    Correct or no? @Vitaliy_Kiselev

  • GlueFactoryBJJGlueFactoryBJJ

    @DrDave - The square root example is an ANALOGY. Since the sensor records data with ~12 bits, but the data is only recorded in 8-bits there is a loss in accuracy. Just like when you take get a square root from a calculator (to, say, 20 decimal places), but are only able to use 3 decimal places when trying to calculate the square. Yes, it was extreme, but I didn't want to use 20 place accurate numbers.

    @Vitaliy - I have tried to show you, repeatedly, even using your own example, that while you can get CLOSE, it isn't (always) EXACT. Which is all I've been trying to say. You keep jumping from one position to another, ignoring/belittling my (and other's) efforts to illustrate my point.

    @GeoffreyKenner - 8-bit contains 256 data points. These are represented as 0-255. Thus, the 255 value in my example. Also, 10-bit is 0-1023 for 1024 data points.

  • Vitaliy_KiselevVitaliy_Kiselev

    I have tried to show you, repeatedly, even using your own example, that while you can get CLOSE, it isn't (always) EXACT.

    Close to what?

    Did you spend time and without emotions just read that had been written?

    It is also good to understand that it is discussion here no one is forcing someone to share any views.

    So, be easy.

  • caveportcaveport

    Jut tried the down convert command line utility mentioned a few pages back..... Quote: Hey guys, I’ve written a really simple command line app for Mac that will resample GH4 footage from 4K 4:2:0 to 2K 4:4:4 using pixel summing. This will give you real 10 bit data in the luminance channel, so it’s not just doing a brute-force bump from 8 bits to 10 bits. There actually is some interesting pixel finagling going on here.

    I did the conversion and brought original mov and dpx files into Resolve for grading. The result? Perfectly preserved 8 bit artefacts. Surprise.

    Yes you can get 10 bit data, but no, it will not look like 10 bit from a camera. End of speculation for me.... I don't guess, I test!

  • Vitaliy_KiselevVitaliy_Kiselev

    Yes you can get 10 bit data, but no, it will not look like 10 bit from a camera. End of speculation for me.... I don't guess, I test!

    Cool, happy for you. It is just not test as it does not have properly defined procedure (add here that no one knows how exactly rescaling is being made) and is all but guess.

  • caveportcaveport

    Vitaliy, I will be very interested if someone can down convert and get a true 10 bit image, but for now it does not exist. I'll leave it to the hardcore coders to make it work. I'll just shoot 10 bit files, it's a hell of a lot easier!!! :-)

  • BurnetRhoadesBurnetRhoades

    Re-scaling doesn't remove artifacts. That was always "wishful thinking" and had been proven already in this thread (page 3). The simple procedure that can be analogous to playing with buckets or balls is going to be the single least effective method of trying to get a free lunch with this stuff. There's no magic. It's not a problem that can really be solved with simple or clever spatial filtering alone.

  • GeoffreyKennerGeoffreyKenner

    Keep in mind also that there's no guarantee at all the sampling of 4 pixels will be closer to a value in the 10 bit space rather than the 8.

  • DrDaveDrDave

    @GlueFactoryBJJ In math, when you make a mistake, you can call it an "analogy," but it is still a mistake. A rounding calculator will correctly reverse an irrational number, and the same is true from digital audio or video, if the code is written properly. Furthermore, an irrational, if algebraic, is easily reversible.

    As far as "identical" goes, there are of course different scenarios depending on dither. You can have two images that are absolutely identical, with the same dither, but which are mathematically different because the dither, although unobservable, is produced by a random number generator in some cases. In this case the math is useless as toll to test whether the images are the same, or produced "losslessly".

  • GlueFactoryBJJGlueFactoryBJJ

    @DrDave - And when you don't like the answer someone else gives you, you can always say they are lying and that they are wrong. Frankly, I don't care if you believe me or not, I know what my intent was when I made the statement.

    Also, don't use rounding as a method of making your assertion correct. Rounding doesn't make for a correct (or precise) answer, it just makes for one that is "good enough". If you like, use the calculator in Windows, take the square root of 7, copy it to the clipboard (~20 places), then clear the calculator, paste the number you have back in and square it. You will get 6.99etc to a large number of places, but NOT 7. As I said, an analogy, extreme, but an analogy.

    When I talk about them not being the same (12-bit RAW vs 8-bit lossy compressed), I'm not talking about rounding errors or the difference because of dither placement due to random number generators (the quality of the random number generator brings up another whole discussion). This is both testable (as has already been done here and other sites across the internet) and proven as a fundamental truth in information theory. Data can be CREATED, but it can't be duplicated once it has gone from 12-bit to 8-bit and back to 10-bit, even with the best of algorithms.

    Even @Vitaliy has admitted as much in an earlier post. Why people keep trying to read more into what I post than what I've said, I just do not understand.

    As I have tried to say in three previous (but edited/deleted) posts. Y'all win. I'm through with this thread!

  • DrDaveDrDave

    @GlueFactoryBJJ no one is saying you are lying, I am simply voicing my opinion that your math is not correct as far as digital media goes. We have a difference of opinion. I explained that the way effects are calculated using placeholders, and I explained why these placeholders allow the NLE to reconstruct exactly algebraic processes. The NLE will not calculate the series to infinity, it will use one of several different systems to deal with that last digit. Now, I could be wrong and you could be right, and my calculator could also be wrong, and my DAW as well. I actually never really wondered about that, I just went as far as checking that if I burn a CD or render an MP3 I get the same "number" each time (which is impossible with dither, for obvious reasons).

    Windows calculator: how to use.

    1. Open calculator. Click view, select "scientific"

    2. Type 2, then the square root button, you will see a long number, but you will see a superscript showing that the computer is recognizing an algebraic process.

    3. Click the x2 button

    4. View the correct answer, which is 2, exactly

    As for rounding, all digital media uses rounding and/or dither to shape the last bit. If you have alternative, I don't know what that would be, but you are welcome to develop your own system. It would be difficult to design a system that holds an infinite number of placeholders, but perhaps by using a closed logic system with a non-binary base you could do that. However, such a system would give you the same results as the one currently in use.

    There is an alternative to rounding/dither which is truncation. Truncation means simply that you throw the last digits away. Certainly an interesting question as to whether in a high bit space any human could tell whether the last bits were dithered or truncated.

    As far as using extra data from downsizing to recreate the extra bits, I would be convinced by a mathematical demonstration of the exact process so if you have one, I would be interested in seeing it.

  • inqb8trinqb8tr

    I am not sure about this: monitor is 1920x1200, but on YouTube when we watch GH4 footage @ 4k it looks much better than when 1080p option is selected. Everybody notices that, right. But, is it just due to YT's higher bit-rate compression for 4k, or some downscaling benefit already kicks in, even in playback? Or what happens? Sorry if this is stupid question, I'm a bit tired right now and my brain refuses to figure anything out on it's own :)

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