Hi there, I am a video engineer working with a Mavic Pro 3 pilot. Recently used the drone for an indoor show featuring many LED video walls. Graphics on the walls contain very saturated colours. Most colours are fine, but fully saturated yellow turns white. Consequently saturated orange and skin tone colours turned very red/pink. We tried different colour settings: Normal, D-Log M, D-Log (with adequate LUT in video processing chain), tried underexposing camera or running in different colour temperature (and correcting brightness/colour temp afterwards), but no joy: bright yellow just looks white. Any ideas how to fix it and get better results?
Hasselblad camera struggling to capture colour space of LED video wall?
- Thread starter katrin
- Start date
I don't know...only raise the question....would shooting with a Cine model using ProRes make a difference? I don't know if ProRes itself has anything to do with color rendition...but I think so...10 bit...more shades might be the exact solution but I think DLog is also 10 bit. Not sure on that count.
Kilrah
Well-Known Member
Probably going to need to underexpose even more. LED displays are typically quite bright, so it's likely that if you can't dim them down temporarily for the shoot you're going to have to underexpose to the point you can't see anything else around...
If you have access to a histogram display, check it for clipping in the highlights of any channel to see what is really going on, and adjust accordingly. If a channel is clipping in a highlight, you will need to adjust your exposure to stop the clipping. There is no way to recover clipped images after the fact.
Since this thread touched on the idea of histograms I'll link this little thing I did for another person showing the changing of exposure and how the histogram reflects those changes. Probably no new to anywhere here .... You'll note that only ISO 400 and 800 are available which is due to shooting DLog.
I understand how this occurred, it is similar to when I was caught out shooting stills of stained glass panels from inside a gloomy church on a day that unexpectedly became very sunny. Your video wall creates the same effect: extreme backlighting blowing colours from 27% reflectance upwards and the camera not having the dynamic range to cope with it. As already mentioned by others, I truly doubt you'll be able to recover something that just isn't there any more.
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One thing you can do, assuming it is an issue with dynamic range is to take multiple exposures at dramatically different levels. I'm assuming that if you lower the exposure values far enough the yellow will look yellow and not white. It may be so much brighter than the other lights that almost everything else is super dark. If you combine those to exposures and mask out everything but the yellow light you may be able to blend them into a single image or video. Obviously with a video if there is movement the masking is more difficult. If, no matter how far you underexpose the yellow light cannot be made into anything but a white light there would be something else going on here. If the other colors are shifting then it may involve multiple exposures. I wonder if you can check the lumens of each light and see if the yellow light is throwing dramatically more lumens out...
BobaFut
Well-Known Member
A Mavic 3 will be shooting 10-bit whether it's outputting H265 D-Log or D-Log in ProRes.
ProRes just has less compression, so it requires less processing power (and preferred by industry pros for that reason, particularly shops that use Macs), but there's no difference in colors and you'd probably get 5 different answers if you asked 3 people if there's an IQ difference between H265 and ProRes. Honestly I don't think anyone could tell them apart in a blind test. On my Sony FX3 (cinema cam), I shoot ProRes 422 to my external recorder and I can't tell the difference between that and the internally-recorded H265 files.
My only guess is that there's some sort of mismatch in the color spaces in the editing pipeline, which could just be a broad DJI color issue or it could be your software or monitor. Have you tried grading the footage manually? Could also be that the LUT is the issue?
You can:
Trim the output settings of the videowall array to decrease luminance of the offending colors. This is probably the best if you are also filming subjects in front of the LED array.
Or, post, do some secondary color correction in the offending hue range of the recording to adjust luminance there. Maybe there’s some headroom there, maybe not.
It may help to put some color patches up on the array and record with the drone - bring the result to an experienced colorist.
It may also help to film a little with a conventional camera and smartphone for a comparison to the Mavic 3 cam.
If the channel luminance is indeed clipping @Dave Maine is entirely correct. Time to pull out the color channel waveform monitor and the vectorscope in post to understand what has been recorded.
Nope; an LED Videowall array is an emissive display. A grey card would only help with a subject that reflects light.
As @BobaFut points out manual grading is going to be essential in a situation like this.
Hi there, thanks so much for the many replies and lots of good ideas. Its a broadcast live production, with the addition of a live drone shot, so unfortunately not much opportunity to do anything too drastic or in post. The LED walls are adjusted for the broadcast cameras, which cope with colours ok. Shoot is only HD SDR, so dynamic range is somewhat limited. I agree underexposing the drone camera might be the way forward, maybe I didn't do enough, but also have the problem that client wants to see surrounding scene AS WELL AS video wall, hence its always going to be a compromise.
@SethB
wish I could adjust LED walls for the drone, but cant due to main cameras being the broadcast cameras and drone only as addition.
have looked at WFM, but failed to switch it to RGB during the event to analyse individual channel clipping in more detail, as for other cameras I normally have it in YCrCb for other workflow reasons...
@Dave Maine
The histogram you spoke about, is that a feature of the drone, like in an SLR camera, can I just superimpose it onto drone o/p? Where do I switch it on/off? Can I have separate histograms for RGB, or just overall brightness levels?
@akdrone
You spoke about still image? Just for my understanding, How is processing of Hasselblad camera of the drone different for still images and video capture? Mavic 3 pro has multiple cameras doesn't it? Only for different focal lengths or do they differ in image quality??
I understand D-Log gives me the greatest dynamic range, doesn't it? What exactly is the difference between D-Log and D-LogM? Is D-Log comparable to our broadcast standards (Sony S-Log, Arri C-Log, PQ or even HLG) Broadcast cameras transmit 10bit as well, so shouldn't be a problem, would only result in slight banding artefacts if quantisation steps too broad. Does drone use full range (0-1023) or limited range (64-940) as standard? I used standard LUTs from DJI website to convert D-Log or D-LogM to SDR/Rec709, someone also made me a custom LUT but that one didn't work for some reason.
What colour space is DJI drone using? Is D-Log more comparable to Rec709 or rec2020 colour space? Does D-Log give me only more dynamic range in brightness? Or in colour as well? @BobaFut you spoke about different colour space and possible "DJI color issue"?
The Hasselblad camera is a single chip camera isn't it? With bayer pattern filter? Is it the same principle as in most single chip cameras or is there anything specific with this particular camera?
Just trying to understand the issue more fundamentally so I can get back to the client to explain why the impossible isn't possible.... Wish I could post example screenshots on here, but cant due to confidentiality.
@SethB
wish I could adjust LED walls for the drone, but cant due to main cameras being the broadcast cameras and drone only as addition.
have looked at WFM, but failed to switch it to RGB during the event to analyse individual channel clipping in more detail, as for other cameras I normally have it in YCrCb for other workflow reasons...
@Dave Maine
The histogram you spoke about, is that a feature of the drone, like in an SLR camera, can I just superimpose it onto drone o/p? Where do I switch it on/off? Can I have separate histograms for RGB, or just overall brightness levels?
@akdrone
You spoke about still image? Just for my understanding, How is processing of Hasselblad camera of the drone different for still images and video capture? Mavic 3 pro has multiple cameras doesn't it? Only for different focal lengths or do they differ in image quality??
I understand D-Log gives me the greatest dynamic range, doesn't it? What exactly is the difference between D-Log and D-LogM? Is D-Log comparable to our broadcast standards (Sony S-Log, Arri C-Log, PQ or even HLG) Broadcast cameras transmit 10bit as well, so shouldn't be a problem, would only result in slight banding artefacts if quantisation steps too broad. Does drone use full range (0-1023) or limited range (64-940) as standard? I used standard LUTs from DJI website to convert D-Log or D-LogM to SDR/Rec709, someone also made me a custom LUT but that one didn't work for some reason.
What colour space is DJI drone using? Is D-Log more comparable to Rec709 or rec2020 colour space? Does D-Log give me only more dynamic range in brightness? Or in colour as well? @BobaFut you spoke about different colour space and possible "DJI color issue"?
The Hasselblad camera is a single chip camera isn't it? With bayer pattern filter? Is it the same principle as in most single chip cameras or is there anything specific with this particular camera?
Just trying to understand the issue more fundamentally so I can get back to the client to explain why the impossible isn't possible.... Wish I could post example screenshots on here, but cant due to confidentiality.
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