Specific Highlight Channel Clipping Issues

This is another post about the highlight rendition on the DJI MAVIC PRO.  The first post was published here.

I received a clip from a Eric Jaakkola pointing to the discontinuous tonal gradation in the highlights under specific situations. The transition between sky and direct orange light from the sun puts a lot of stress on these small sensors. Here’s the before and after of a D-LOG (+1:-2;0) Auto WB frame. Eric pointed to that darker yellow halo around the sun. We can also see it shifts towards green, making it a very unpleasing and unrealistic image. The LUT being used here is ICARUS V.2.1 DJI MAVIC PRO D-LOG Sunny WB – sRGB – High Key_64 point. 

Measurements

Here are the RGB values on the original frame. We can see the red and green channels clipping before reaching peak white,  leading to a yellow halo around the sun. 

ICARUS LUTs deal with this pure yellow not knowing that it sits at the edge of pure white, thus correcting it as was designated to do so with the calibration charts used. This leads to the darker, greenish tone we saw in the first example. There’s the possibility that Auto WB is to blame here. Then again, I wasn’t there when this video was shot, so I don’t know how intense was that orange/yellow sunset shot by Eric.

A less dramatic case

Here is another example, this time shot with sunny white balance.  Channel clipping ain’t that dramatic and presents the transition between sky and sun in a more pleasing manner. Notice how the LUT fixes the salmon tinted ring around the yellow area, creating a smoother transition but it can’t insert information where there’s none, just two clipped channels and blue at 38.

Using the corrective LUT

At this point I considered the option of creating a LUT that corrected this artefact. Since recovering clipped channel values is impossible to do with a LUT only, my approach was to clip the yellow color all together while maintaining a pleasing and smooth transition into pure white. Here we see the original D-LOG frame corrected with a LUT that fixed the yellow halo. Beware that this correction will affect the presence of pure yellow (and it’s transition into surrounding colours) anywhere in your image so beware of it’s use.

 

Example 1

 

Example 2

Native
Corrected

 

Using the corrective LUT followed by another ICARUS LUT

Subsequently, any other LUT can be applied. Here we see the original D-LOG clip and a transformed version with the corrective LUT and an ICARUS LUT applied in serial. Notice how the transition is smoothed out even further.

Example 1

Example 2

 

Using secondaries

Of course the ideal situation would be to use a precise, dedicated, secondary color correction in your NLE. Here we see the original D-LOG frame and a transformed version with custom made secondaries and an ICARUS LUT applied in serial, plus a custom grade. Everything looks better now, we have an even smoother transition between sky and pure white, no noticeable halos and an overall pleasing, well exposed and vivid image.

Example 1

 

Example 2. This is clearly the best of all. The yellow halo was selected, darkened and color was added so it would match the surrounding orange and interior peak white. We get a very smooth transition to peak white and a wider perceived dynamic range. Remember that highlight roll-off is as important as dynamic range.

 

This corrective LUT is being distributed for free. Download it here
ICARUS Yellow Highlight Channel Clipping Fix

Have you encountered such situations? If so, send me a short clip and I’ll look into your case.

Cheers

 

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