Obtain dense depth images with the RandomDot Projector

This tutorial shows how to set up the rc_visard with the RandomDot Projector to increase the density of depth images, as shown in Fig. 12. This is particularly recommended for objects and workspaces with little or no visual texture.


Fig. 12 A scene including objects without visual texture (i.e. the intensity of the image is uniform over large parts of the scene) and the reconstructed depth image without RandomDot Projector (center) and with RandomDot Projector (right).


This tutorial assumes that the previous tutorial Tuning of Image Parameters has been completed.

Before we start

Before going through this tutorial, the following prerequisites should be met.

  1. The rc_visard’s has the latest firmware image and the rc_visard’s license includes the IOControl component. This can be verified on the Web GUI’s System panel.
  2. The RandomDot Projector, the network cable connecting it to the rc_visard, and a 24 V, 60 W power supply are available.


Please ensure that a 24 V, 60 W power supply is used for powering rc_visard and RandomDot Projector together.


The RandomDot Projector is controlled via the GPIO Out 1 of the rc_visard (cfr. IO and Projector Control). In this tutorial, Out 1 mode refers to the RandomDot Projector mode.

Mounting the projector

Mounting the projector is described in detail in the projector’s manual. Please see Installation.

Focusing the projector

For the focus configuration, one should turn the RandomDot Projector permanently on. This can be done on the Web GUI’s IOControl panel available in the Modules tab by setting the Out 1 mode to High.

Before focusing the projector, one needs to remove the lens protection tube temporarily. Please unscrew the lens protection tube patently, until the rings of the lens are visible. Now, the focus can be adjusted by rotating one of the rings of the lens until the random dot pattern is sharp (Fig. 13).


Fig. 13 Blurred (left) and sharp (right) random dot pattern.

Configuring the aperture of the projector

For the aperture configuration, one should set the Exposure mode to Auto in the Web GUI’s Camera panel.

The aperture controls the brightness of the image with the random dot pattern and is adjusted by rotating one of the rings of the lens.

For its configuration, one should look at the Confidence image in the Web GUI’s Depth Image panel and reduce the aperture as much as possible, while still achieving good confidence over the whole image (i.e. as much white pixels as possible, Fig. 14).


Fig. 14 Maximum (top) and optimal (bottom) aperture of the projector. The confidence images do not present significant differences.

Selecting projector working mode

Single shot mode

If the projector is used in combination with rc_reason modules (ItemPick, BoxPick or SilhouetteMatch) it can work in a single shot mode. This means that it will only be activated on demand when the module request a new depth images.

To enable this mode the Single + Out1 Acquisition Mode has to be chosen in Depth Image tab.

Continuous mode

If the projector has to be used in continuous mode (stereo matching is performed continuously without a trigger) the proper Out 1 mode in Web GUI’s IOControl has to be set.

By default, the Out 1 mode of the rc_visard is set to Low, i.e. projector is off.

Typically, the user needs to select the ExposureAlternateActive Out 1 mode, in which the RandomDot Projector is on only for the exposure time of every second image. Images with projected pattern are used for computing depth images. Images without projected pattern can be used as texture or for other image processing modules.

Configuring the exposure

As last step, one needs to go back to the Web GUI’s Camera panel and set the exposure time, either manually, as explained in the Exposure and Gain Settings section of the Tuning of Image Parameters tutorial, or automatically using the auto exposure. In this case, the Auto Exposure Mode should be set to AdaptiveOut1 to avoid over exposure due to the projector.


If the exposure is configured to automatic mode, when the projector is turned on, it may take a few seconds until the exposure and gain settings become stable.

More optimization tricks

In some cases, the density of the depth image can be further optimized by changing the focus of the RandomDot Projector to introduce some blur in the projected pattern. This can be done while looking at the Confidence image in the Web GUI’s Depth Image panel and trying to obtain as much white pixels as possible.

If the camera image includes highlights that are not reconstructed in the depth image (Fig. 15), one can verify whether these highlights are introduced by the RandomDot Projector (e.g. by simply turning the projector off). In such case, we recommend to change the mounting of the RandomDot Projector, in order to have a different angle between the rc_visard and the projector itself. Reducing the aperture of the projector can also help in removing highlights.


Fig. 15 Highlight in the camera image due to the RandomDot Projector.