Wouldn't a ND Grad filter be cool on dashcams?

Paul Iddon

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Many of us (most or all?) experience the problem that the brightness of the sky compared to the houses and trees etc in the lower half of the dashcam view causes the sky to bleach out or the buildings etc to look dark.

How useful then do you think a simple small graduated neutral density filter be, that could be slotted or attached over the lens?


Discuss.
 
Most of us solve this issue by aiming the cam to capture less sky, which is usually the brightest part being captured. I like my cam to capture overhead traffic signals which are common here. That limits how far downward I can aim it. It would be good to see what results could be had with a filter like this ;)

Phil
 
...It would be good to see what results could be had with a filter like this ;)

Phil
A small piece of appropriately colored cellophane taped partially in front of the lens would not be difficult to do. I think I have some colored gel samples laying around somewhere collecting dust I could play with if I can find them.
 
Wouldn't a filter like that make it harder to capture details at night? For example traffic lights, street names, etc.
Seems to me like this should be controlled by software.
 
Wouldn't a filter like that make it harder to capture details at night? For example traffic lights, street names, etc.
Seems to me like this should be controlled by software.
Yep, at night it would have the exact opposite of the desired effect versus daytime - but at night there's nothing in the sky that's worthwhile to record, it would just make the dark sky darker.

Edit: The filter would only be applied to the upper portion of the frame so the lower half would be unaffected. There might be some unintended impact on the overall exposure though depending on how individual cameras determine the proper exposure.
 
This topic has been discussed here on DCT quite a few times before. One guy even put a piece of opaque black electrical tape across the top of his lens feeling he had solved his problem, except for the fact that doing so will seriously compromise the len's ability to gather light in other scenarios as if it had a dramatically smaller aperture. Even though a graduated filter will work, that too can degrade the lenses ability to gather light at night and no filmmaker or photographer would likely ever use an ND filter at night. I would tend to agree with @Saw Master that the best approach is to adjust the camera upwards or downwards until you find the optimal exposure "sweet spot".

That's not to say you can't do this. My vehicle happens to have a five inch wide strip of blue tint across the top of the windshield. At one time several years ago, I experimented with mounting a dash camera in a position so that the tint strip would encroach slightly into the FOV in such a way as to act like an ND filter across the top of the image and cut down on bright sky issues. It actually worked quite well, except that it resulted in unnaturally blue skies. (which I found quite tolerable) Notice though how much darker the pine trees in the upper right side of the frame appear behind the tint strip.

GT300W parkinglot.jpg

Little by little we are seeing new sensors and improved DSPs that are improving the historically abysmal dynamic range of dash cams. Eventually, we will have cameras that will make the problem of overly bright skies or blown out license plate numbers at night when illuminated by headlights a thing of the past. The Mobius 2 camera originally used a dual frame HDR technique that was remarkably effective. It would capture two simultaneous frames, one over-exposed and one under-exposed and combine them into a single image. Unfortunately, the technique caused other video capture issues and had to be abandoned. Nevertheless, it was a sign of what is possible.
 
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I think HDR is probably the way forward, combined with a good metering system.
Viofo are developing HDR for their A119. This example shows how HDR is capable of limiting burned-out highlights at night:
hdr-testing-jpg.33304


The Akenori NX01 that I tested last year had a very wide dynamic range. It was the best feature about this camera. Shame it wasn't released. These daytime and night time examples show what it was capable of, by comparison to a Mobius1 and SG9665GC.
2016-11-28-nx01_m1_gc-jpg.27679

2016-11-23-nx01_gc-jpg.27684
 
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