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Does an external recorder bypass the camera colour science?


DevonChris

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Using an external recorder such as the Atamos Assassin bypasses the recording restrictions, and obviously bypasses the compression algos, but does it also bypass the camera colourimetry too?

I currently use Nikons mainly because the OOC colours are so good, but I want the benefits of external recording (higher bit rates, longer recording times etc). What I don't want is for the externally recorded data to lose those great Nikon colours. Would that happen?

Thanks

Chris

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It would be interesting to see a signal processing diagram that clearly articulated the exact changes made to the image at the point where it is internally recorded.  And, conversely, what signal processing is possibly bypassed for the HDMI output path.

For example, speaking only of the A7Si/ii, I believe that the video levels recorded internally vs. the HDMI output are legal vs. full range, respectively.  And, as Andrew pointed out above, the noise profiles are also significantly different -- and I, too, have trouble attributing them to compression averaging.

I suspect there are other tweaks going on.  But, but I agree that the basic color science is probably upstream of all of those tweaks.

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So the signal passed through the HDMI path is not raw as happens with the Canons with ML hacks, but most go through significant processing in camera.

Does this mean that using an external recorder is not a good idea unless you have a 10 bit output and 8 bit internal as you get with the GH4?

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I have always wondered what is responsible for the degradation of noise grain texture (it's so blotchy over uncompressed HDMI) compared to the raw sensor data, it can't be compression.

Pretty simple. You bypass the internal processing . You have to simulate/replicate the internal processing. It is a bit of of a black box but it is safe to assume that noise reduction is the key item.

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So the signal passed through the HDMI path is not raw as happens with the Canons with ML hacks, but most go through significant processing in camera.

Does this mean that using an external recorder is not a good idea unless you have a 10 bit output and 8 bit internal as you get with the GH4?

I'm not sure what camera you are using, but even with a camera whose HDMI output is constrained to 8-bit, an external recorder may allow for 4:2:2 as opposed to an internal 4:2:0.  Additionally, an external recorder will typically allow for a more professional, higher-bitrate, less compressed codec (e.g.: Prores, DNxHD, DNxHR) that also might significantly accelerate your postproduction workflow.

Edit:  Lastly, if you are shooting sync sound, an external recorder will also possibly provide more professional connectivity options for microphones, higher quality mic preamps -- and maybe a more intuitive interface for controlling gain levels. 

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No, "colour science" is effectively a group of processes that happen before this output. They even happen before raw. So don't worry!

Not sure it's that simple.  There certainly must be generally shared image processing methods, but, no doubt, some cameras process their images differently at various stages.

 

Actually, I am not sure if their is an agreed-upon definition of "color science."

 

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I'm not sure what camera you are using, but even with a camera whose HDMI output is constrained to 8-bit, an external recorder may allow for 4:2:2 as opposed to an internal 4:2:0.  Additionally, an external recorder will typically allow for a more professional, higher-bitrate, less compressed codec (e.g.: Prores, DNxHD, DNxHR) that also might significantly accelerate your postproduction workflow.

Edit:  Lastly, if you are shooting sync sound, an external recorder will also possibly provide more professional connectivity options for microphones, higher quality mic preamps -- and maybe a more intuitive interface for controlling gain levels. 

Currently using 2 x hacked Nikon D5200's but they have issues with only streaming out HDMI @30fps no matter what the frame rate is set at. I am considering upgrading to D750's or GH4's.

Definitely good to get the higher bit rates with an external recorder and to use Prores, however if the Nikons stream 8 bit 4:2:0 over HDMI then do the external recorders upscale to 10 bit 4:2:2, which is not good IMO?

That's a very good point about the audio connectivity with an Atomos etc. I currently sync sound to an external audio recorder, so that would be one less box to worry about :D

 

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... however if the Nikons stream 8 bit 4:2:0 over HDMI then do the external recorders upscale to 10 bit 4:2:2, which is not good IMO?

I currently sync sound to an external audio recorder, so that would be one less box to worry about :D

 

Although you can capture an 8-bit signal with a 10-bit recording device -- you gain nothing.  You cannot manufacture those two extra bits of bit depth -- they much be captured and encoded by the source device. 

The same holds true for color sampling, with the exception that you can achieve gains by downscaling a 4k 4:2:0 signal -- to an HD resolution. 

Lastly, from an audio perspective, not only is it one less box to worry about, it completely avoids the arduous syncing process, as well as ensuring a perfect lock between audio and video (which many DSLR camera fail to do -- even when recording internally). 

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