High Dynamic Range Technique by TOPPAN 3D ToF Sensor

We would like to introduce one of the High Dynamic Range (HDR) techniques that can be achieved with our 3D Time of Flight (ToF) sensor.

TOPPAN ToF’s HDR

HDR technique for image sensors typically uses the fusion of multiple images(frames) with different exposure times to create a single HDR image(frame).

Similarly, 3D ToF sensors often use HDR techniques based on the frame fusion technique. However, the disadvantage of HDR by frame fusion is that the frame rate decreases depending on the number of frames used for fusion. For example, a ToF camera operating at 30 fps would drop to 15 fps by a two-frame fusion. This means that the dynamic depth resolution is dropped in half, which would make it difficult to perform 3D sensing of fast-moving objects.

To address this issue, our 3D ToF sensor uses a “line binning” method for HDR, where data with different exposure times are captured for each pixel line of the sensor and then combined to produce HDR data.

While this approach would decrease the static depth resolution compared to HDR with the frame fusion method, it does not compromise the frame rate. In other words, it allows high-speed 3D capturing without compromising dynamic depth resolution. Therefore, this HDR method is highly effective in applications such as autonomous robots, and person/object recognition systems, where capturing fast-moving objects in a wide range is more crucial.

HDR Demo Experiment

・The distance from the camera to the wall is approximately 7 meters.
・A person holding a box moves from 7 meters away to near the camera.

Demonstration Video

Explanation

Normal Operation (Targets: Wall @ 7m, Person @ ~1m)

Left image: Point could image
Right image: Infrared image

As the person gets closer to the camera, IR signal saturation causes inaccurate distance calculations, resulting in depth data degradation.

HDR Operation (Targets: Wall @ 7m, Person @ ~1m)

This experiment shows that the HDR mode effectively reduces depth errors (= IR signal saturation) at close distances, while also allowing sensing up to around 7 meters at the same time.

We are currently working to improve the performance and quality of this HDR feature. If you are interested in TOPPAN ToF sensors, please feel free to contact us. We would be pleased to hear from you.
TOPPAN TOF SENSOR AND CAMERA