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transcoding tool vs flight time correct exposure

Discussion in 'Pro/Adv Discussion' started by dimedrol, Oct 4, 2015.

  1. dimedrol

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    I noticed that transcoding tool is recommended to use with Phantom flight recordings made in LOG mode. When I record my videos in that mode they look overexposed, so I really want to add negative expocorrection most of the time. Not only the image looks overexposed, but it is shown as overexposed (zebra strips) in the app. But as I make the adjustment during a flight, the final video when run through the transcoding tool appears underexposed. Means the tool disregards my adjustment as if I had not made it and does what it would do on the non-adjusted material.

    As an experienced (over 7 years) DSLR user I know that precise exposition at the shot time is crucial for end result, because yes, you can recover certain information from overexposed areas but that amount is very limited even in my full frame camera, not to mention the tiny compact Phantom 3 one.

    So that makes me wonder, why does Phantom 3 automatically overexpose videos in LOG mode and try to fix it at transcoding time and is it really any better than shooting with precise exposition?

    I really like the idea of shooting videos in some equivalent of raw mode, but then it looks like I have no control over the camera, because what I see in the app (overexposed image) is not what I get (after transcoding tool), so I have no idea if my interruption may be useful.
     
    #1 dimedrol, Oct 4, 2015
    Last edited: Oct 4, 2015
  2. flying treasure

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    I'll have to look up the transcoding took because I don't know what that is. I just started shooting a few weeks ago. But I've done video production for 15 years now all over the world and have used dslr and know what you mean about this image in log mode. I've been shooting in regular right out of the box setting because it actually looks really great to me. Most of the time things are blow out. I know it's not a long term solution but I don't know what to do either. I will say I think the camera corrects better than dslr though, do you? Is it a 4.2.2 color space? I thought I read that somewhere were as most dslr is 4.2.0.
     
  3. dimedrol

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    Transcoding tool does some sort of post processing that is only (as far as I understood) applicable to videos made in LOG mode. I think of it as a kind of a raw converter. I have no idea what it really does though and why does it need the image to look overexposed in the app at shoting time.


    The reason I started to shoot in log mode is my dissatisfaction with Phantom 3 auto exposure. I don't know what kind of metering phantom camera does (I think matrix metering would be appropriate) but in many situations I found it's image begging for adjustment. So I found the transcoding tool and thought of it as an intelligent post-processing exposure adjustment utility.
     
    #3 dimedrol, Oct 4, 2015
    Last edited: Oct 4, 2015
  4. flying treasure

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    I saw and downloaded it when I first got my phantom but though it doesn't shoot in RAW video so why do I need a converter.
     
  5. dimedrol

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  6. flying treasure

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    Interesting! I'm going to look more into this!
     
  7. John Lo

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    You can not give a high hope to the cmos sensor in p3 which is like a 2 yearsold mobile phone camera.

    It may help to preserve some highlight and shadow detail if u record in log mode, but only a bit because the poor performance of the cmos.
     
  8. flying treasure

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    2 year old mobile phone camera? It looks better than that to me.
     
  9. bobmyers

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    SAY WHAT? Better send yours back if it isn't better that that. :D:D
     
  10. EPT160

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    The P3P does not shoot video in any sort of RAW file. The P3P on board video processor converts all video shot to any of the user selected profiles including LOG, at the very low bit rate of 60 Mbps in a 8 bit colour space of 4:2:0. They (the Testing Inspire 1 LOG Mode in Nepal forum thread) talk about converting this stream into ProRes YUV4:2:2(10bit) stream, with a higher bitrate of near 350 Mbps. You can do this for the sake of producing a more friendly format for your editing platform but you can not increase the dynamic range or add any extra data (video information) to your already captured file.

    LOG is good in high contrast scenes, but if you are shooting already flat light situations then you are missing out on some of the dynamic range of the 60 Mbps capture.
     
    #10 EPT160, Oct 5, 2015
    Last edited: Oct 6, 2015
  11. apsphoto

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    As EPT160 stated so well, the transcoding tool is for converting to another format for editing. It does nothing to exposure, it cannot add dynamic range and it cannot create data that is not there. It is just a change in format and bit rate. The data you recorded is the data you get. If you overexposed and blew out the highlights then you cannot recover it, if it is only slightly overexposed then you might be able to salvage the highlight details. Since they are using a limited bit depth you get a limited dynamic range, if the bit depth and data rate where higher then you could extract more details. A trade off in design vs price for marketing.

    Alan
     
  12. dimedrol

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    What is the advantage of LOG mode, can anyone explain? How is it better than normal mode?
     
  13. apsphoto

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    LOG mode will give you a flat non-contrasty image, so if possible the highlights and shadows are not clipped. LOG mode allows you to set the black and white points and the contrast curve to match what you want in post processing. LOG mode does not save exposures, the exposure is still whatever you want, but LOG mode is a profile that makes it easier to color grade the video so that you can create the mood and look that you want. It is not a "raw" it is just a way of capturing a neutral looking scene for later editing.

    Alan
     
  14. dimedrol

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    Alan, help me understand it.... LOG mode captures dynamic range NN, same as Standard mode, does it? Means it has the same amount of information, so where does the extra information for more flexibility in the post-processing come from? Do you mean to say that in standard mode P3 applies some kind of autocontrast/curves to make image look more juicy and that is where the loss occur?
     
  15. flying treasure

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    Thanks for letting me know it's just a converter. I do video for a living so I'll just use other tools to convert instead of this transcoded.
     
  16. flying treasure

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    Think of it as how it takes the image in. The censor responds to light differently in log mode. So it knows that the brights should not be registered as bright and e darks not registered as dark. On a scopes scale once over 100% white and once below 0% dark you will lose detail in those areas. So if you tell the censor to respond to those areas differently you can capture as much detail in those areas without losing it because of the extremes of the exposures.

    Look up video curves to understand what's happening more.
     
  17. apsphoto

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    Yes that is exactly it, that is how the different modes look they apply curves while the LOG mode is more linear to bordering on a reverse contrast curve.

    Alan
     
  18. dimedrol

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    On a bright sunny day no even 35mm sensor I know can capture the dynamic range that our eye sees (well maybe except for Fuji S5Pro). So clipping is inavoidable. In which case, what can LOG mode add, I guess nothing. That is why my guess was that LOG mode doesn't bring anything new to the image, it's just standard mode takes something away as a part of image processing.

    Look what I found

    Here's my P3 flying over a river, camera mode=auto. On the first image notice the amount of sky - it's about 12% of the image. And everything else looks nicely exposed
    [​IMG]

    then the second image is slightly different, it has less sky in it, and see what happens: p3 automatically raises the exposure to match the first image in average brightness. It is obviously overexposed, as a result

    [​IMG]

    If it indeed works the way I described, then apparently it can't be perfect in many situations
     
    #18 dimedrol, Oct 6, 2015
    Last edited: Oct 6, 2015