How to deal with ripples

The Gaussian Smoothing Filter and Noise Suppression Filter can help in removing ripples because they improve absolute noise in the point cloud and suppress more systematic noise, like ripples.

참고

잔물결을 지속적으로 억제하기 위해 대부분의 시나리오에서 Sigma 은 가우시안 필터와 함께 자주 사용되는 것보다 높게 설정됩니다.

Why can ripples occur in the point cloud?

Ripples or waves in the point cloud occur due to interreflections. An example of ripples can be seen below where the ripples vary in their shape, frequency and amplitude. Hence, this type of point cloud artifact is more systematic in its behavior than other types of noise. Ripples are often challenging for use cases using shiny bins because interreflections from the outer bin wall onto the bin floor easily occur. For the same reason, it can also make it difficult to detect objects within the bin because the objects may be deformed by ripples. This can be an issue for captures taken with the Phase Engine since it is not as resilient against reflections as the Stripe Engine or Omni Engine. However, for strict time budgets, the Phase Engine is often preferred due to its speed.

이 튜토리얼에 표시된 이미지는 외부 빈 벽에서 빈 바닥으로의 상호 반사가 빈 바닥에 봉투를 배치하여 강조되는 위의 2D 이미지에 제공된 시나리오를 기반으로 합니다. 2D 이미지에서 봉투의 빈 벽에서 빛 반사가 있음을 분명히 알 수 있습니다.

For very shiny bins, ripples often occur due to interreflections from the outer bin wall onto the bin floor and objects.	The ripples on the bin floor are smoothed out with the Gaussian filter. A sigma value of 2 is applied in this scenario.

Ripple suppression step by step

1. Phase Engine 사용하여 캡처합니다.

   참고

   For captures taken with the Stripe Engine or Omni Engine, the ripple effect is minimal and it should therefore not be necessary to suppress ripples. If your capture time budget allows it, select the Stripe engine to better preserve edges since it does not require the same level of Gaussian smoothing as the Phase engine. Note that the Omni Engine applies some smoothing by itself. If you still have the ripples with these engines, enable Noise Filter Suppression.

2. Zivid Studio에서 잔물결이 있는 포인트 클라우드 영역을 확대합니다.

   • 잔물결이 있는 영역의 깊이에 대한 Z 범위를 조정하여 깊이 맵을 사용할 수도 있습니다. 깊이 제한이 충분히 엄격하게 설정되면 Z 구성 요소의 색상 차이가 표시됩니다. 그런 다음 잔물결의 극한 위로 마우스를 가져가서 잔물결의 최소값과 최대값 간의 차이를 표시할 수 있습니다.

3. Enable Noise Filter Suppression and check whether the ripples are removed or reduced like shown in the above figure.

   • 잔물결이 제거되거나 감소되었는지 확인하려면 이전 항목에서 설명한 대로 Depth 맵을 사용하십시오.

4. If not sufficient, increase the Gaussian Filter sigma until the ripples are either removed or reduced.

5. Finally, it is essential to evaluate how the filtering has impacted the edges and shapes in the scene. The figures below show how these features are affected by smoothing for the given scenario.

   • Are the objects intact enough for the algorithms that your application is running to be able to determine valid pick poses? For instance, for CAD-based matching, this is an especially important topic. Hence, in some scenarios, you must compromise between allowing some ripple effects to keep the object shapes and edges intact. For such scenarios, decrease sigma or disable Suppression until a tradeoff is found.

   • Note that the contrast distortion correction filter adds additional smoothing as shown in the rightmost figure below. Typically, contrast distortion artifacts are encountered for high-contrast scenes, such as for shiny metal cylinders. For these types of scenes, the contrast distortion correction filter should not be turned off since it is important for maintaining cylindrical shape. For all other scenarios where your scene allows it, it is recommended to turn off the Contrast Distortion Filter.

An example of an edge where there are data points on both the upper surface and adjacent surfaces.	This type of edge is smoothed when the Gaussian filter is used for ripple suppression.	The edge is more smoothed when the Gaussian filter and the contrast distortion filter are combined.

An example of an edge where there are only data points on the top surface due to its position relative to the projector.	This type of edge is minimally smoothed when the Gaussian filter is used for ripple suppression.