With the increasing prevalence of non-contact 3D scanning in recent years, people are faced with two specific types of 3D scanners more often than others: laser and white light. It is easy to get confused about how these two technologies compare with each other. Here is a brief overview of each technology:
3D Laser Scanners
Laser scanners use laser light to scan parts. 3D laser scanners commonly found today are either:
- handheld where the stripe sweeps over the part like a paint gun or,
- tripod mounted where the laser line sweeps across a field to cover an area
The handheld type is either attached to an arm or has targets on the handheld fixture to give constant readout of where the scanner is at any time. Another way to align data (which is shared with all 3D scanning) is to put photogrammetry markers on the parts as a basis for aligning scans into a complete 3D model.
3D White Light Scanners
White light scanners are usually tripod-mounted, where a fringe pattern is generated by scanner's projector and is laid over an area at a time over the scan object. Within the scanning time, the fringe is modified in width and phase and the 3D scanner extracts the 3D coordinates from calculating the returned patterns. The term “white light” comes from the fact that the bulb is a white light generator. Recently, blue LED light is being used as a replacement so the term may need to accommodate blue light scanning. A more general description is called structured light scanning, which covers all colors.
Here is a list of comparisons between laser and white light scanners. This list is not exhaustive but it gives a general idea of the simliarities and differences between them:
Technology: 3D laser scanners sample the world one time as the line passes the illuminated subject. White light scanners sample the world many times, with fringe patterns varying width and phase that redundantly estimate the shape of the subject. Due to the repeatability of the readings, the accuracy of a white light scanner can be (and has been shown to be) inherently better than laser scanner.
Speed: Laser scanners have a potential speed advantage since they can do a single sweep much faster than the multiple fringes of white light. With advanced cameras, throughput electronics, and faster processors, white light cameras have been sped up to capture a scan in less than one second with over a million points. Due to their fast scanning speed, white light scanners are especially useful in face scanning and body scanning applications where people have difficulties staying still.
Area Scanning: Laser scanners are generally based on a point that is split into a line, which is then swept across a field. They are performing area scanning by stretching from a one-dimensional line to two-dimensional area. White light scanners are true area scanners by the very nature of the projected patterns being on the entire area continuously and repeatedly.
Lighting Conditions: Laser scanners have the ability to turn up the gain to get some data in difficult ambient lighting environments, albeit noisy and inaccurate data. White light scanners are limited by the light intensity output of the bulb and contrast level of the projector. In office or industrial settings, using a white light scanner is generally not a problem, but there are other locations (such as outdoors) where this could matter.
Safety: Lasers, due to their ability to focus light intensity and energy into very small space, have an inherent safety issue. The biggest concern is eye-safety danger. Some of the lasers used in 3D laser scanners today are not rated for being Eye-Safe. There are laser systems intended for human scanning such as body, face, or feet scanning. These systems need to be rated for Eye-Safe and are certified to be below Class 2M.
White light scanners, being based on simple white light, don't have that problem and are much less concern for users, HR departments, and OSHA regulators. Other structured light scanners, such as blue light scanning, are also not a concern for safety since they are not dealing with the intense light.
In summary, each technology has their own strengths and weaknesses. Selecting which type of technology most suitable for your project largely depends on project requirements (ie. scanning object, scanning environment, accuracy, resolution) as well as downstream application (what the user intends to do with the 3D scan data).Do you have any questions or comments related to white light and laser scanners? Please post in the comments section.
This blog post was previously posted on Mon, Dec 19, 2011 on 3D3 Solutions blog. LMI Technologies acquired 3D3 Solutions on May 1, 2013.
Posted by Thomas Tong