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DJI please let me choose the ISO for D_LOG
633 13 2017-8-4
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DroneADservice
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Hello DJI,

Can somebody from your team chime in and give a clear explanation how to work with the noisy D-LOG format? since they changed the settings to a fixed ISO (500) it's a pain to work with.
I had a shoot with a Television team from Helsinki (in ProRes HQ) and they insisted to use the D-LOG...i insisted to use the standart beceause of this known issue of the actually very noisy D-LOG format!!!

It didn't take a long time before they came back to me for exactly this problem......................

I would know please when you release a fix to switch off the fixed ISO.


Thank you for a reply

Patrick
2017-8-4
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JoePGM
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I'm also very disappoint with the D-LOG quality. For me I'm not prores user but general H264/265 recording on SD card. The footage looks really noisy and rough while color grading in davici resolve....
2017-8-4
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raven4
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I regret to tell you that DLOG is a very unfortunate choice for H264/265 footage. Any 8-bit format is not recommended for log recording because the 8-bit format doesn't have the digital resolution to effectively use Log gamma. As for using Dlog with Prores, one must be very precise with the exposure levels.DJI will never allow variable ISO with Dlog because the nature of Dlog requires exposure to a precise point on the gamma curve. ISO is only a convenient label, anyway. If you want to shoot Dlog at , say, ISO 250, simply set the exposure for ISO500 and open the aperture 1 f-stop.
2017-8-4
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Altitude Drones
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It would be great if we had the same choice of colour looks in ProRes as we do in h264.

I really like D Cinelike but find DLOG way too flat. Standard has way too much contrast.

Could this be done in a firmware update?
2017-8-5
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dancopter
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raven4 Posted at 2017-8-4 14:33
I regret to tell you that DLOG is a very unfortunate choice for H264/265 footage. Any 8-bit format is not recommended for log recording because the 8-bit format doesn't have the digital resolution to effectively use Log gamma. As for using Dlog with Prores, one must be very precise with the exposure levels.DJI will never allow variable ISO with Dlog because the nature of Dlog requires exposure to a precise point on the gamma curve. ISO is only a convenient label, anyway. If you want to shoot Dlog at , say, ISO 250, simply set the exposure for ISO500 and open the aperture 1 f-stop.

Don't you mean close the aperture?
2017-8-5
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raven4
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dancopter Posted at 2017-8-5 04:56
Don't you mean close the aperture?

Nope....ISO 250 is not as light sensitive as ISO 500 by 1 stop. Therefore, one would be shooting at 1-stop more open if the camera was set to half the ISO."Dlog is too flat".... reflects a basic misunderstanding of what log footage is. It's designed to be post processed. Not meant to be used. as is, directly out of the camera.
2017-8-5
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DJI Mindy
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D-Log has been improved. The dynamic range in D-Log becomes larger, and the default ISO is higher due to the change of the gamma curve. In D-Log, when gain is set to 1, ISO is 500 and the dynamic range is the largest.
However, if gain of a sensor is increased, dynamic range will be decreased and noises will become more obvious. So, currently, ISO is set to 500 for optimal dynamic range in D-Log. Whether or not ISO can be set to a higher value will be determined after image quality evaluation and configuration. DJI is working on this.Thanks for your understanding.
2017-8-7
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DroneADservice
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DJI Mindy Posted at 2017-8-7 23:45
D-Log has been improved. The dynamic range in D-Log becomes larger, and the default ISO is higher due to the change of the gamma curve. In D-Log, when gain is set to 1, ISO is 500 and the dynamic range is the largest.
However, if gain of a sensor is increased, dynamic range will be decreased and noises will become more obvious. So, currently, ISO is set to 500 for optimal dynamic range in D-Log. Whether or not ISO can be set to a higher value will be determined after image quality evaluation and configuration. DJI is working on this.Thanks for your understanding.

Thanks for your reply DJI Mindy,

After reading the explanations of you and the other forum members the reasons for the fixed ISO is more clear.
However i like to know if there's a turnaround to avoid the excessive noise in the shadow zones please.
I guess if i put the exposure to the right i can maybe recover the shadows with less noise???

Thanks for some hints

Patrick
2017-8-9
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DJI Mindy
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DroneADservice Posted at 2017-8-9 07:47
Thanks for your reply DJI Mindy,

After reading the explanations of you and the other forum members the reasons for the fixed ISO is more clear.

Due to the hardware limit, the noise will appear more or less in the dark zones, we would suggest to reduce the noise with third party program.
2017-8-10
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Barry Goyette
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Patrick -- Like almost all Log Gammas, D-LOG does show some noise in the shadow areas. I wouldn't call it excessive noise. I'd say its less noisy than most log gammas I've worked with from Canon, Sony and previous DJI versions of D=Log. By Design, LOG gammas are designed to give maximum dynamic range and flexibility in post by foregoing the tone compression that happens in the shadow and highlight areas of a typical rec709 linear gamma. Two factors are at work here: one is the LOG encoding itself which assigns relatively equal amounts of encoding values to each stop of dynamic range...and the second is by essentially "underexposing" the sensor to allow for maximum DR in the Highlights. DJI has determined, rightly, that ISO 500 is  the best trade off between DR and noise. As Log gammas go...D-Log is pretty good, although DJI's lack of documentation, LUTs and propensity for changing it whenever they feel like it are slightly problematic.

The problem with the noise being "excessive" thus,  falls to the user. If you're not used to LOG exposure, it's pretty common for people to expose "normally" and then complain about the noise in the image. Log exposures do best when the exposure is increased to the point where the brightest highlights are nearly clipping, often referred to as exposing to the right,( the reasoning behind it in LOG gammas is slightly different that why is is done conventionally with linear gammas, but the result is largely similar). Because of how LOG gammas are encoded, there is generally no penalty for exposing this way, and so, your goal is to use that extended DR to maximize exposure to the sensor (something difficult to do with linear gammas because of the compression mentioned earlier).

Your exposure in Log should generally look 1-2 stops brighter than normal, and when you process the image in post, as you mentioned, you pull everything down, including "crushing" that shadow detail which will eliminate or minimize the noise you are seeing.  I recently did a test of a 3 stop exposure ramp with D-log where the darkest exposure had typical D-Log noise in the shadows, and the brightest simply had no noise at all....this was on a relatively challenging backlit scene with trees against a sky and dark shadows in the foreground. D-log had enough range to handle this with a 3 stop increase in exposure, and produce exceptionally clean results. The more dynamic range the scene has, the less you'll be able to ramp the exposure, but you should, generally increase it until important highlights are just below clipping. There are times when you'll have to compromise...for instance when the sun is in the shot...as 13 stops of DR won't let you see the sunspots and have clean shadows at the same time.
2017-8-10
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raven4
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"....The more dynamic range the scene has, the less you'll be able to ramp the exposure, but you should, generally increase it until important highlights are just below clipping. There are times when you'll have to compromise...for instance when the sun is in the shot...as 13 stops of DR won't let you see the sunspots and have clean shadows at the same time."

Since REC709 has a total DR of 6 stops, it's also pretty problemmatic to "decode" a 12-13 stop image on a REC709 display. In fact, in images that contain sun, it becomes necessary to do a little masking and exposure adjustment in post. In other words, exposing to the right, such that specular hilites are captured fairly accurately, requires that I selectively bring up the shadows in post. Exposing for the mids or lows, clips the hi's, and no post recovery of the hi's is possible. It becomes rather a tradeoff of noise or clipping in a REC709 display.Once I figured how to take a 12.5 stop DR image, I am learning how to effectively display that image in REC709.

2017-8-10
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DroneADservice
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Hello Barry and Raven4,

Thank you very much for this exhaustive and good explanations. That's exactly what i needed to know.

Patrick

2017-8-14
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Barry Goyette
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raven4 Posted at 2017-8-10 12:21
"....The more dynamic range the scene has, the less you'll be able to ramp the exposure, but you should, generally increase it until important highlights are just below clipping. There are times when you'll have to compromise...for instance when the sun is in the shot...as 13 stops of DR won't let you see the sunspots and have clean shadows at the same time."

Since REC709 has a total DR of 6 stops, it's also pretty problemmatic to "decode" a 12-13 stop image on a REC709 display. In fact, in images that contain sun, it becomes necessary to do a little masking and exposure adjustment in post. In other words, exposing to the right, such that specular hilites are captured fairly accurately, requires that I selectively bring up the shadows in post. Exposing for the mids or lows, clips the hi's, and no post recovery of the hi's is possible. It becomes rather a tradeoff of noise or clipping in a REC709 display.Once I figured how to take a 12.5 stop DR image, I am learning how to effectively display that image in REC709.

This is always the "catch" with systems that capture more than Rec709, and why on other forums (I'm looking at you DPReview) i've argued that continual focus on cameras with the highest DR isn't necessarily the best use of our energy. The reality is of course that the easiest way to shoot 13 stop log and fit it in Rec 709 is to simply apply a rec709 gamma curve  (LUT) ...but then what's the point? Well that's what 100% of broadcast shows shot on 14+ stop Alexa's do. All that extra DR, currently, only exists to allow you to mask or "power window" parts of the image, allowing you to bring things into Rec709 that normal wouldn't fit. The future though is more challenging. As we move into an HDR world where monitors are capable of displaying 10-20stops of DR, we find that almost all of that increased DR is in the highlights...and that it become even more important to "light" our way towards getting mid-tones bright enough that they "read" like a rec 709 curve. (the problem is quite visible by viewing a samsung SUHD display at your local best buy...which basically has rec 709 skin tones and highlights that blind you every few seconds...that's not what good HDR looks like (I've seen good HDR at the Canon booth and it's a thing to behold, but also incredibly hard to achieve)).  I guess what I'm saying is enjoy it now, while things are still easy :-)
2017-8-15
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raven4
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Barry Goyette Posted at 2017-8-15 08:10
This is always the "catch" with systems that capture more than Rec709, and why on other forums (I'm looking at you DPReview) i've argued that continual focus on cameras with the highest DR isn't necessarily the best use of our energy. The reality is of course that the easiest way to shoot 13 stop log and fit it in Rec 709 is to simply apply a rec709 gamma curve  (LUT) ...but then what's the point? Well that's what 100% of broadcast shows shot on 14+ stop Alexa's do. All that extra DR, currently, only exists to allow you to mask or "power window" parts of the image, allowing you to bring things into Rec709 that normal wouldn't fit. The future though is more challenging. As we move into an HDR world where monitors are capable of displaying 10-20stops of DR, we find that almost all of that increased DR is in the highlights...and that it become even more important to "light" our way towards getting mid-tones bright enough that they "read" like a rec 709 curve. (the problem is quite visible by viewing a samsung SUHD display at your local best buy...which basically has rec 709 skin tones and highlights that blind you every few seconds...that's not what good HDR looks like (I've seen good HDR at the Canon booth and it's a thing to behold, but also incredibly hard to achieve)).  I guess what I'm saying is enjoy it now, while things are still easy :-)

well said, barry!
2017-8-15
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