6 Replies Latest reply on Sep 27, 2018 3:49 PM by jakeding

    External LED Projector VS Depth Quality



      I recently use the external LED projector to project 640x360(totally 230,400 dots) dots onto the subject. I did so since the Best Known Method paper says the external project will improve the depth quality. Actually I found the projector does help in the current environment.


      My questions are:

      1. When I turn the room light on, I can barely see the projected random dots. Suppose that the room light is brighter than what I have in the following figure 2, can D400 camera sensor see the projected dots which is invisible for human eyes?


      Figure 1 dark room with projector



      Figure 2 bright room with projector


      2. I can't understand the following words in the BKM paper: We normally recommend patterns that are scale invariant. This means that if the separation between the projector and the depth sensor changes, then the depth sensor will still see texture across a large range of distances.




        • 1. Re: External LED Projector VS Depth Quality

          1.  There is a relationship between the camera's Laser Power setting and the dot visibility.  The lower that Laser Power is set at, the less visible the pattern becomes.


          2.  The dot pattern can provide the camera with texture detail to lock onto to enhance depth image results in situations where there are surfaces with low texture detail, such as walls and doors.


          3.  You can move the projector a distance away from the camera's depth sensor without negatively impacting the amount of texture that the camera sees.

          • 2. Re: External LED Projector VS Depth Quality

            Hi MartyG,

            Thanks for the prompt answer!


            However you may misunderstand my questions. I know how to tune up the internal projector's laser power. The projector I used in the figure is an external LED projector rather than a laser projector.


            So my question is: if the room light or even sun light is brighter than the projected dots pattern from LED projector, can the sensor still see the dots pattern? In this situation, human can't see the dots pattern by naked eyes anyway.




            • 3. Re: External LED Projector VS Depth Quality

              I realized what you meant and came back to amend my answer, but you had already replied. 


              The 400 Series cameras perform even better in strong light, and texture detail is increased by that light.  So in strong light, the camera should not need the dot pattern to provide texture.


              Re: Noise in Realsense D435 pointcloud


              I realize that is not what you were asking though.  You wanted to know how the visibility to the cameras depth sensor of your external projector's dot pattern would be affected.   Jesus G from Intel Support has stated, "D400 works with both IR and Visible light.  For Indoors, it has the IR projector to illuminate scenes with low texture and if IR is not reflected on certain surfaces such as carpets, the stereo camera works off of visible light."


              So I would speculate that if the camera cannot see the pattern of your external projector then it will analyze based on visible light like it does with its own projector,

              • 4. Re: External LED Projector VS Depth Quality

                I appreciate your answer! So can I think in this way: If the room light is brighter than the projector's light in which the dots is invisible to human eyes, then the camera won't take advantage of the projected dots pattern anymore.



                • 5. Re: External LED Projector VS Depth Quality

                  Your evaluation of the situation is a good one, I believe.  It may still be worth using the projector though, judging by your image of the lit room.  The dots are slightly visible as a white-ish covering, so may help the camera to see darker surfaces (black / grey) in the same way that spraying fine powder like foot powder or baby powder on a surface does.

                  • 6. Re: External LED Projector VS Depth Quality

                    Good idea to add powders on the body. Thanks!