ICARUS LUTs – About Dynamic Range, Highlight Roll-Off and Channel Clipping

New recommended contrast settings for D-LOG

V2 is coming and it addresses a series of problems with the MAVIC’s D-LOG response. We’re seeing better results with contrast set at -1  instead of -2. By looking at the way my charts clip in the highlights, I’ve seen that there is no real advantage in shooting -2. It just lowers the highlights and raises the blacks, thus compressing the existing DR without any advantages. On the contrary, it puts more stress on the already fragile H.264 60MB/s file. Having a slightly lower white point isn’t necessarily a bad thing as I’ll explain with the examples below.

About Dynamic Range

Also, DJI D-LOG, on the MAVIC at least, is more like a flat curve with a lot of highlight compression. This makes sense because it addresses some problems with small sensor cameras, namely low dynamic range in the highlights, and favours landscape shots by compressing strong reflections in water, clouds in the sky, etc. Let’s call it an aerial footage friendly curve rather than true LOG. This compression can be restored with a LUT and doing the same with D-Cinelike is trickier and leads to more posterisation and a less smooth roll-off.  
D-LOG +1;-2;0 Sunny gamma response curve tested with a Colorchecker Video
 

Smooth highlights

See that dent in the curve above? V.2 LUTs restore details in the highlights in a realistic manner, while preserving a smooth roll-off into pure white. Smooth roll-off is as important as dynamic range because it is makes a digital image perceptually pleasing. This holds water from iPhones to Alexa’s. In the example below, notice how the halo surrounding the sun is almost invisible in the original D-LOG frame. Also, that warm mist in the horizon is restored without any harsh posterisation artefacts. White levels are kept a hair below 254 to account for any unforeseen variation in the video levels.

Channel clipping

Digital cameras have an issue with some channels clipping sooner than others. In a pseudo-log format like D-LOG, dialled at -1 contrast, this is quite evident. Here we see a bright sun, against a blue/orange gradient. On the left, at the #2 picker, notice how the green channel almost clips at 235 (considering that pure white in D-LOG is 236;236;236) whereas, on the right, a corrective LUT restores a natural colour balance, even when the red channel clipping at 255 on the #5 picker. Do you have any questions? Send me an email to icarus@paulocunhamartins.com Fly safe, have fun!  

4 Replies to “ICARUS LUTs – About Dynamic Range, Highlight Roll-Off and Channel Clipping”

  1. Hi Paulo, Very interesting BLOG about some very technical stuff. Can you clarify a bit about the visual difference between using a LUT v2 on D- log and D- cinelike? I guess the high tech equipment and techniques allow to show the benefit of using Dlog but can I see this in a real picture or video? Keep up the good work and I’ll try to learn from your BLOG. Looking forward to the release of your new LUT pack V2 ! 🙂

    1. Hi Geert, thank you.
      D-LOG offers more flexibility in post, a softer roll-off in the shadows and highlights, colours feel smoother and there is an overall feel of a better picture coming from a better camera. D-Cine is more of a finished, closer to real, color mode. It requires way less correction from the upcoming v.2 LUTs but there’s a difference there, otherwise I wouldn’t be making them in the first place 😉 Apparently, the majority of MAVIC users go for D-Cine and that’s good thing. You get a good looking picture that requires less tweaking in post, you can go from editing to publishing quicker. Still, there are some corrections happening and I’ll address the differences in an upcoming blog post.
      Cheers

Leave a Reply

Your email address will not be published. Required fields are marked *