Glossy surfaces and depth sensor on D415

PAlca2 · ‎01-16-2019

Hello everyone, this is my first post in this forum.

I have been working lately with a RealSense camera (the D415 model to be precise). Although many tests have been extremely succesful, we are having a problem now regarding the depth sensor.

I attach here as an example the color frame and the corresponding depth frame of an image. As you can see, from this background alone, there is a lot of noise and several points that, though being way over the 30cm limit, are not recognized by the camera (the black spots on the right image). My guess is that the glossy surfaces are affecting the depth sensor of the camera, do you think this might be the issue?

If so, the walls in the hallway [the region of interest, vertically the pixels from zero to ~300] can be painted to mitigate this effect. So my follow up question is: is there any specific paint that I should be looking for that works best? I tend to think that any opaque paint with low IR reflectivity would do the trick, but maybe someone else here has encountered this issue and made more extensive tests.

Thank you very much!

MartyG · ‎01-16-2019

I could not find an attachment on your message. If you pasted it in then it will not show in the message - it has to be loaded in via the 'Image' button on the toolbar at the bottom of the message writing box.

Glossy / reflective surfaces will have a negative impact on a depth image and may show up as solid black areas, especially if there is a strong light-source such as a bright ceiling light in the location that is magnifying the reflection. Black or dark grey surfaces can also appear as empty black areas on the image, because that color absorbs the camera's light.

It is possible to dampen reflectivity on large surfaces by using a fine spray-on powder such as baby powder or foot powder. I have heard an anecdote about a car repair bodyshop that was being scanned, and they coated the entire room in baby powder! An advantage of such powder is that it will be far easier to remove than anti-reflective paint.

There are also professional 3D scanning sprays available to dampen reflections, such as this one:

https://www.laserdesign.com/3d-scan-spray/?language=en_US

PAlca2 · ‎01-17-2019

Thanks MartyG for your answer. I had indeed forgotten to attach the image, now I have edited the post.

I read about the baby powder to avoid reflections, yet these surfaces will be exposed to frictional contact that can remove the powder. I thought that the baby powder alternative was due to its necessity of applying non-destructive coatings to the surfaces (who would want to paint the whole room green just to take a picture 😅 ). If that is indeed the case, then I clarify that I am completely free to paint this walls however I like or applying any other permanent or semi-permanent coating.

I will look further at the link you sent, thanks!

MartyG · ‎01-17-2019

An example of use of anti-reflective applications is when scanning jewelry, which a jeweler company might do when creating images for their website. Another example is a convention kiosk, where the lighting or the kiosk wall / table surfaces might be disruptive to a camera-based product that is being demonstrated.

Another alternative anti-glare product is a thin film, such as the 1m wide roll in the example link below that can be used on windows.

http://www.mecanusa.com/polarizer/AR-film/AR_roll.htm

If you are able to use non-reflective paint on your walls though then there is certainly nothing to stop you from doing that! During my research into such paints, I found that some of them are intended for outdoor use only because they contain solvents. So make sure to find one that is indoor-friendly.

There is also apparently a difference between the terms 'anti-glare' and 'anti-reflective', as described here:

https://www.tspinc.com/anti-glare-vs-anti-reflective/

PAlca2 · ‎01-17-2019

That difference between glare and reflection is indeed a very good I had been thinking about. I am not a native English speaker, so the subtleties between the terms are kind of hard for me to grasp.

However, trying to think about it, I suppose that maybe the biggest difference is between the concepts of matte-glossy. If so, I think that a matte paint might do the trick. I will try on different paints and let you know if I find anyone that works best.

Thank you very much Marty