UK unlocks a new method of photometric stereo imaging

With the support of the EPSRC QuantIC research program in the UK, a team from the Photonics Institute of the University of Strathclyde and the Bristol Robotics Laboratory has developed a new method photometric stereo imaging: from a fixed camera perspective and different direction of led lighting illumination creates a 3D image. This achieves an improvement to Photometric Stereo (PS) imaging technology.


 
The team focus on exploring the potential functions of LED lighting lamps in the early research. In 2018, they put forward the concept of "lighting as a service": LED provides imaging lighting and visible light communication, 3D imaging is used to automatically monitor activities in an area, and at the same time, it provides wireless connection for robot agents in the same space.
 
Technological breakthrough
 
Theoretically, it should be able to be used for robot navigation, process control, surveillance applications and security and public locations, and structural monitoring if PS imaging technology is effectively used.
 
But he reality is very skinny. The inherent complexity of traditional PS technology stop it from being effectively used in the existing building infrastructure: first, it needs to be compatible with PS special lighting in indoor or outdoor lighting devices; second, it needs to use a lot of cables to connect the camera and the light source. Handover with each other to synchronize the lighting system and the image acquisition system.
 
If the difficulties of practical operation can be overcome, PS imaging technology can pave the way for 3D imaging to enter industrial or security applications, bringing a more direct visualization method.
 
This difficulty was overcome by the University of Strathclyde in the United Kingdom. According to a study published in The Optical Society (OSA) magazine Optics Express, the researchers demonstrated that 3D optical imaging can be performed with mobile phones and LEDs, compatible with standard lighting infrastructure, and does not require artificial synchronization of cameras and lighting.
 
The researchers found that when objects are illuminated from top to bottom but are imaged from the side, 3D images can also be reconstructed. This arrangement allows the overhead light source to be used for lighting.
 
Le Francois, a PhD student in the research team, said: "As far as we know, we are the first system that combines a top-down lighting system with side image acquisition, where the light modulation is self-synchronized with the camera. We hope to eliminate The connection between the light source and the camera makes photometric stereo imaging easier to deploy."
 
To synchronize fiber acquisition and lighting, researchers also developed algorithms which modulate each LED in a different way. This is like a fingerprint that allows the camera to determine which LED produced which image. The new modulation method also carries its own clock signal, which is passively detected by the camera, and enables the image capture to be synchronized itself with the LED. By using handheld mobile phone camera to record imaging data, and then automatically use the team's algorithm to process into 3D images.
 
Demonstration of a small sculpture printed with matt material
 
The researchers used their modulation scheme with a photometric stereo setup based on commercially available LEDs to show us the new method: a simple Arduino board provides electronic control of the LEDs, and the high-speed video mode of a smartphone provides image capture. The demonstration object is a small statue of 48 mm high. They use 3D printing to make the figurine with matte materials to prevent any shiny surface which might complicate imaging from affecting the presentation.
 
After determining the best location for the LED and smartphone, the researchers achieved a reconstruction error of only 2.6 mm when imaging the figurine from 42 cm away. This error rate shows that the quality of the reconstruction is comparable to other photometric stereo imaging methods. They also reconstructed a moving object image and proved that this method is unaffected by ambient light.
 
The project pointed out in its published paper: "These efforts achieve PS imaging without synchronization, reduce flickering, and achieve compatibility with led ceiling lamps and wall-mounted and mobile cameras. In this case, PS imaging will be compatible with light. Guaranteed. Reality (LiFi) networks or visible light positioning (VLP) exist together, achieving all these functions as well as general lighting by using the same led lights."
 
Le Francois added: "Deploying an intelligent lighting system indoors allows any camera in the room to use light and retrieve 3D information from the surrounding environment. LEDs are exploring more application areas, such as optical communication, visible light positioning and imaging . This is not nonsense."