The MERLIN robot has two kinds of visual sensors, AXIS camera and PMD camera. AXIS camera provides a high resolution color image with a large field of view, while PMD offers a range image of the scene. PMD (Photonic Mixer Device), based on optical time-of-flight principle, provides the possibility of measuring distances for 2D scene in real-time. With the LED array, it emits infrared light and measures the phase difference between the incident and internal reference signals. The distance information is thereby calculated for every pixel with the phase differences. Along with the range image, a grayscale intensity image and amplitude image can also be acquired for image processing, e.g. edge detection.
PMD can be used in various applications in fields as diverse as automotive, manufacturing, robotics, spacecraft docking and multimedia. With robust, high speed and accurate distance information for every pixel, previous computer vision techniques could be significantly strengthened. One major disadvantage of PMD is the relatively low resolution or corresponding limited field of view. The newest version of ToF camera has a resolution of 204x204 (PMD CamCube 2.0). For this reason, high resolution AXIS camera is combined in our research with PMD to generate an RGBZ image.