Intel realsense d435f shows no improvement over d435 on surface with reflections?
Hello,
I have been using the d435 for some time on a system that operates close to the ground, and I was interested in the d435f, as the d435 has issues on surfaces with reflections whereas the d435f is advertised to help with this problem. Typically with the d435, I am able to get a dense depth map of the ground in front of the camera, but on surfaces with reflections, there is always a big hole of invalid values in the depth map. However, when I set up the d435f and compared it to the d435, I see similar or worse performance on surfaces with reflections (i.e. there is still a big hole in the depth map). Although I do notice that the IR pattern is intensified in the IR images for the d435f.
Is anyone else having better luck with the d435f? Is there maybe some configuration needed in the software to get better performance on surfaces with reflections?
For some more context, the camera is about 0.15 m off the ground and I am using the ShortRangePreset.json from here (https://dev.intelrealsense.com/docs/d400-series-visual-presets). I tried the others too, but ShortRangePreset.json worked best near the ground. I am using the realsense-viewer executable included with librealsense and am on the latest version.
Thank you for your time!
Best,
John D'Angelo
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Hi John Dangelo The filter on the D435f blocks out visible light frequencies but allows higher near-infrared frequencies to enter the sensor. It sounds as though the infrared sensors may be being saturated by the reflections.
Please try setting an Auto-Exposure Region of Interest (ROI) in the lower half of the camera's view to see whether this improves the depth image by better handling the glare from reflections. If you are using the RealSense Viewer software then point 3 of the section of Intel's camera tuning guide linked to below provides guidance for doing this.
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Hi MartyG, thank you for your feedback. I modified the Auto-exposure ROI (I tried the bottom half of the camera's view, I also tried adjusting the setpoint for the Auto-exposure as suggested in point 3 of that section), and that reduced the reflection in the IR image but did not remove it entirely nor did it have much of an effect on the hole in the depth map. Same result on the d435 and d435f.
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In the Post-Processing filter list in the options side-panel of the RealSense Viewer, if you expand open the settings of the Spatial Filter by clicking on the arrow icon beside it then there is a drop-down menu for 'Hole-Filling', which is set to none by default. Select Unlimited from the drop-down and the Spatial filter should automatically fill in holes in the depth image.
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Thank you for your suggestions. I am aware that there are post-processing options to help with this kind of problem (believe me, I have tried almost every slider and toggle button in the realsense-viewer many times trying to solve this problem). I will also note that (at least in my experience) the hole filling filter does not work well on large holes. Qualitatively, it makes the depth image heatmap look a bit nicer, but it produces artifacts when I try to deproject the processed depth image to 3D.
The main point of my post was the hardware side of the problem. The IR-pass filter on the d435f does not seem to solve the problem of light reflecting on flat surfaces, saturating the IR sensor, and messing up portions of the depth map with invalid or incorrect depth values (whereas I was under the impression that it was targeted at solving this kind of problem). It is also possible that because of the height I have the camera at, the angle of the light reflecting off the surface makes the problem much worse than if the camera were higher off the ground.
I think I will give this another read: https://dev.intelrealsense.com/docs/optical-filters-for-intel-realsense-depth-cameras-d400 and perhaps try a linear polarizing filter instead.
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It would also be worth exploring using the HDR (High Dynamic Range) feature to deal with reflections by using two distinct exposure values.
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