A change in color of the sky when landing a plane.

[sam81]

I'm using a Mobius 2 for recording landings and I notice a change in the color of the sky as soon as I touch down. Not sure if it's a Mobius 2 issue or something that just happens in all dash cams. I feel it's the latter since it might have something to do with receiving a different amount of light as I flare (slightly pull back and nose-up the plane immediately preceding touchdown), but not entirely sure.

Link to video. At the 40-second mark, the sky loses that nice deep blue color.

 

[DT MI]

... it might have something to do with receiving a different amount of light...

Definitely a matter of auto exposure. The flare likely has little to do with it anywhere near as much as the overall exposure.

Look again at the 40 second mark and you'll see that up to that point the lower portion of the frame consisted of general ground clutter, followed by primarily white paint on the runway. At the same time as the sky changing color you got to the portion of the runway that wasn't painted, but was black. This caused the AE logic in the camera to increase the exposure causing the upper portion of the frame to lighten.

The reason for the exposure adjustment is simply that most dash cams use some degree of 'center weighting' when determining exposure. When you introduced the much darker runway into the frame the effect was to reduce the light level hitting the sensor and the exposure was adjusted accordingly.

Bottom line - your suspicion is correct, but for a slightly different reason.

 

[Nigel]

It is a change in the auto white balance as the grey of the runway becomes dominant, occurs immediately after crossing the white markings.

The exposure hardly changes, but the ratio of red increases dramatically.

If the Mobius has an option for fixed white balance then that would probably solve the issue, although you might then need to adjust the colour balance in the editor for some videos such as when flying into a sunset. Much easier to do that than to try and correct a video that used auto white balance when flying though, unless you fly like the Red Bull Air Racers where you may actually need changes during a video!

Edit: I see a comment in another forum "The latest firmware has custom and lockable white balance." - try that...

 

[DT MI]

It is a change in the auto white balance as the grey of the runway becomes dominant, occurs immediately after crossing the white markings.

The exposure hardly changes, but the ratio of red increases dramatically.

....

Since gray tones (including white and black) are inherently neutral being made of up essentially equal parts of RG&B how is it that adding gray to an image would trigger a change in the auto white balance? (Something you should know if you'd read and understood the tutorial I referred you to less than a month ago in this posting which shows, among other things, that neutral density filters are always gray specifically because they do not affect color balance - https://dashcamtalk.com/forum/threads/how-is-the-video-quality-for-you-guys.45553/page-2#post-558286 )

Second question - in what color space does increasing the ratio of red 'dramatically' cause the sky to go from a dark blue to a lighter blue (i.e. a change in exposure) versus shifting the color towards purple/violet?

 

[Nigel]

Since gray tones (including white and black) are inherently neutral being made of up essentially equal parts of RG&B how is it that adding gray to an image would trigger a change in the auto white balance?

The grey has a lower proportion of red than either the grass or the white paint, it is not a perfect grey, so the auto white balance decided that the colour of the light source had changed and adjusted accordingly.

Second question - in what color space does increasing the ratio of red 'dramatically' cause the sky to go from a dark blue to a lighter blue (i.e. a change in exposure) versus shifting the color towards purple/violet?

At first sight, without doing lots of checks, it appears that the exposure change is a result of incorrect gamma processing in the Mobius, but there may be another cause.

However the main change is a shift in colour balance, increasing the proportion of red to compensate for there being a lower proportion of red in the grey runway.