Color mode & Dynamic Range

Andrei V · Dec 4, 2016

I tested four color modes to compare the dynamic range. In each case, I exposed to try to protect highlights/shadow details and avoid zebras triggering on the clouds/white sections of the ship:

I don't see much dynamic range difference between them. The Dcinelike profile seems to preserve a bit more highlight detail, but that's partially because the exposure is 2/3 of a stop lower. Art is quite similar to Dcinelike. Dlog is... well, very compressed for my tastes. And not clearly retaining more highlight or shadow detail.

I then went ahead and graded them (just a contrast boost) to try to fill up more of the waveform without losing any details. Here are the results:

My conclusions:

* Dlog preserves less detail in the highlights than the other modes! (check out the clouds in the upper right corner). This might be because I overexposed the dlog shot (even though in the histogram/waveform it doesn't look overexposed -- but note the strange clipping at IRE 65 on the right hand side of the vectorscope. Perhaps the histogram in DJI Go 4 is not accurate when dealing with dlog.
* Dcinelike and Art have similar dynamic range, but Art is less saturated and may have a slight color shift. In any event, I don't see much point in experimenting further with Art.
* As between None and Dcinelike; Dcinelike appears to preserve a bit more detail in the clouds. Could be because it's 2/3 of a stop underexposed as compared to None. Despite being 2/3 of a stop lower exposure than None, Dcinelike seems to lift the shadows, so the underexposure isn't creating any shadow/black clipping. Still, as between the two, I think even after grading None looks nicer/more contrasty/has more pop.
* I need to test None vs. Dcinelike vs Dlog all 1 stop underexposed (and at the same exposure) to reach a definite conclusion as to highlight/shadow retention.

tml4191 · Dec 4, 2016

THanks^ please keep us posted with your results

CactusJackSlade · Dec 4, 2016

Thanks for sharing your work

Dronefriend · Dec 4, 2016

Nice to see a follow up on this.. I came to the same conclusion with my P3S, to avoid d-log and shoot in None. D-log simply squeezes more information over less data.. leaving the extremes empty. So when you unsqueeze in Resolve or Premiere or whatever, you're left with less than what you might have had if you didnt compress it with d-log in the firstplace.

Always nice with screenshots as these though, great work

phneeley · Dec 4, 2016

This is great info! Many thanks for sharing! What are your thoughts on go-to, pre-grade settings for Contrast, Sharpness, and Saturation?

Sent from my iPad using PhantomPilots

Dronefriend · Dec 4, 2016

Id like to hear Andreis thoughts on this as well. I have always gone for -1 / 0 / 0 myself. Sharp, con, sat

smiller · Dec 4, 2016

Is there any detail or description anywhere of what the various color modes ('Art', 'Dcinelike', etc.) are supposed to do? Are they nothing more than canned custom settings, or ..? For instance DLog is supposed to perform a special function (although whether it does so very well or not is apparently another matter), is all of this documented anywhere (beyond trying to infer what you can from dozens of forum threads)? The DJI user manual is typically useless but there must be something on paper somewhere?

KevMo Photog · Dec 4, 2016

Still looks like D-cinelike and none are the best choices for overall detail in all tones. I have been using none on my P4 for 9 months now. It seems to be the best for sure! Thanks for your testing here for sure!

yannick_c · Dec 4, 2016

The purpose of flat/log modes vs normal modes is to get more dynamic range.
It's really well explained here :

Log mode is even better than flat modes cause it give the same amount of data for each stops.

But that's the theory, and DJI doesn't seem to implement that "real log style" in their D-LOG mode. It looks like they just take the normal range and apply some curve and compression on it . Why they do that ? I don't know. Maybe due to some limitation with the sensor or with the processor.

Tomas Wangen · Dec 4, 2016

I did a high-contrast test today and from what I can see, absolutely nothing is gained using log for the phantom 4 pro. It seems rgb-range is simply compressed right before saving giving loss of details in both highlights and shadows and also color. Attached is a sample, only difference being none (lefthand side) and log (righthand side). The scopes shows that the same area around the sun looses details for both log and none.

There is some discrepancy in tone (this was the closest I was able to get in Resolve) and I had to turn up saturation to 100 for the log-sample.

The small difference in angle is due to a minor consistent rotation most likely caused by my inability to calibrate IMU 1.

Conclusion: Use None

Andrei V · Dec 4, 2016

It's been raining here constantly for the past day or so, so I haven't been able to do the follow-up testing I wanted to do yet.

Regarding sharpening/contrast/saturation settings -- my testing indicates that the contrast setting only expands or contracts the range of the waveform in which information is being recorded. It doesn't actually affect how much information is retained or discarded in the highlights and shadows. Decreasing contrast works similarly to going into dlog mode -- as Dronefriend explained, going with a negative contrast simply squeezes the same information over less data.. leaving the extremes empty. So I see no benefit to changing the contrast from 0.

Similarly, I don't see much point in lowering the saturation, since (for my tastes and purposes) I just end up boosting it again in post.

Sharpening is more intersting. If you zoom in at 400% on 4k video, I can see sharpening halos at 0, -1 and even -2.. only -3 looks clean, but it's also very soft:

I need to do a bit more testing with sharpening in post and comparing the results with sharpening in camera, but I imagine I'll settle on something like -2 or -3.

99% of the footage I've shot over the last 6 months with the P4 has been using Color: None and 0/0/0. I expect I'll end up using the same settings with the P4P, though I may end up turning sharpening down to -2 or so and applying sharpening in post. It depends on how the results look (and the fact that I have no sharpening plugin for FCPX currently).

Raptorman0909 · Dec 4, 2016

I did some more testing today and have some interesting observations. I'll upload the video tomorrow as it will take a while to edit.

What I did was set the drone up without props in a location outside that had lots of contrast and did six tests using the following settings:

1. All video shot at ISO100, f/6.3 and using 'Custom' style at -2, -2, -2 (Sharpness, Contrast, Saturation) -- the only adjustment for exposure was to vary the shutter speed from 1/500 to 1/50. So, the exposure was fully manual.

2. I tested with 'Color' profiles "D-Cinelike", "None", and "Art" using H.265

3. I tested with 'Color' profiles "D-Cinelike", "None", and "Art" using H.264

4. In each of the 6 tests I started with a shutter speed of 1/500 and stepped it down in 1/3 stop intervals until I got to 1/50. Then I stepped it back up to 1/500.

My observation is that even with the "None" color profile, which should do nothing to the dynamic range, that the floor was about 7 IRE in the deepest shadow at 1/500 and that floor only increased to about 8.5 IRE at 1/50. The bit values at 1/500 were 14/13/13 (RGB) and at 1/50 they were 20/21/20 (RGB) with an IRE of 7. At the highlight end the values were as follows: at 1/500 127/133/145 (RGB) with an IRE of 55 and at 1/50 247/250/255 (RGB) with an IRE of 95.

So, it appears that with the None profile, which should do nothing to the contrast, but also using the Custom setting of -2, -2, -2 for sharpness, contrast and saturation, that the custom setting with the -2 contrast is setting a floor of about 7 IRE and 13 bit value and also setting a ceiling of about 95 IRE and 255 bit value. It looks like the contrast adjustment is not doing what it's supposed to and should likely be set to zero.

Again, I need to work on editing this and I hope to upload tomorrow. I may look at testing the effect of the Custom contrast setting to see how that effect the floor and ceiling.

And as a final update ... I had two more issues with gimbal homing so I will have to send the drone back -- Arrrggghhh...

Brian

Andrei V · Dec 4, 2016

Brian -- your results regarding contrast match with my findings. Lowering contrast, like using dlog, seems to just be squeezing all the information into a smaller data space (i.e. shifting the black and white points inwards) rather than expanding the range of data being recorded. So yeah.. you'll get the same dynamic range whether you leave it at -3 or 0, so to get the cleanest data with the most gradations, you're better off leaving it at 0.

Here is how contrast effects the floor and ceiling (all shot in Color: None, same exposure, Sharpness/Saturation 0)

Basically, Contrast 0 uses the 0IRE-115IRE; -1 5IRE-110IRE; -2 around 10IRE-105IRE and -3 15IRE-100IRE.

It's linearly compressing the IRE range used to represent the image, not limiting itself to the mid-tone contrast.

Aramis · Dec 5, 2016

Andrei V said:
In each case, I exposed to try to protect highlights/shadow details and avoid zebras triggering on the clouds/white sections of the ship

Wonder how it is possible to expose to protect both highlights AND shadows ?!!
If highlights and shadows are preserved, there is no dynamic range problem.
Depending on the scene (and the way you want to render it) you expose for the highlights (and recover the shadows in post prod) or you expose for the shadows (and recover the highlights if possible).
Or you expose in the middle (which is not protecting HL/SH)

Raptorman0909 · Dec 5, 2016

As promised, here's my exposure tests using "D-Cinelike", "None", and "Art".

Brian

2nd2non · Dec 5, 2016

@Raptorman0909
Great information Brian!
I suppose we have to take the good with the bad from DJI [emoji15]
So if I follow you, the maximum DR can be achieved with None profile. However, though this may be ok for color correcting an image only, it would make grading a bit more difficult. As such, I suspect D-Cinelog or Art may be better for those wanting to grade at a small sacrifice of DR, correct?

Sent from my iPhone using Tapatalk

Raptorman0909 · Dec 5, 2016

2nd2non said:
@Raptorman0909
Great information Brian!
I suppose we have to take the good with the bad from DJI [emoji15]
So if I follow you, the maximum DR can be achieved with None profile. However, though this may be ok for color correcting an image only, it would make grading a bit more difficult. As such, I suspect D-Cinelog or Art may be better for those wanting to grade at a small sacrifice of DR, correct?

Sent from my iPhone using Tapatalk

You know, I'm still trying to wrap my head around what DJI is doing and can't say I know for sure or even what the best approach one should take. My first flight using D-Log really bothered me both because it still has the flickering I-frame reset thing the Inspire 1 Pro has and also because of the way the dynamic range is being processed before being packaged by the H.264 or H.265 codec. To really understand this would require someone with professional experience with the way image processing works at the hardware then software level. Way beyond my pay grade.

I hope DJI can figure this out at some point but in the mean time we need to make the best use of the cruddy tools DJI has given us. To that end the color profiles that are most likely to be useful are D-Cinelike, None and Art but beyond those gross settings there are other knobs to tweak and that includes the adjustment of Sharpness, Contrast and Saturation. My next tests will try to understand what those settings are doing and what the best values should be.

The goal is getting the best video and images and we may have to accept a less than perfect set of techniques given the utter failure of DJI to implement image processing and codec work properly.

Brian