3D Scanning Technology: Comparative Analysis of Fringe Projection, Laser Scanning and Speckle Scanning

With the rapid development of science and technology, 3D scanning technology plays an increasingly important role in many fields such as medicine, industry, art design, etc. This article aims to conduct an in-depth comparative analysis of the three mainstream 3D scanning technologies: grating, laser, and speckle. We will explore their principles, advantages, disadvantages, and application scenarios to help you make an informed decision when choosing a scanning device.

Ⅰ. Fringe Projection: Excels in detail preservation

1. Principle

Fringe Projection methods generally utilize mechanical gratings or DLP projectors to cast multiple sets of phase-shifted sinusoidal stripes and Gray coded stripes. The phase-shifted stripes are used for precise phase calculation, while the encoded stripes assist in the positioning and matching of the periodic phase stripes. Cameras simultaneously capture the structured light images of objects’ surfaces that have been encoded with Gray codes and subjected to phase-shifted stripe projection. Using the phase-shifted images, the wrapped phase is calculated, and then the absolute phase is further deduced using the encoded stripes. Stereo matching of data with identical phases retrieves image disparities for 3D reconstruction. In a typical working scenario, a DLP projector usually projects eight Gray coded stripe patterns and four phase-shifted stripe patterns. During operation, it is essential to maintain the stability of both the equipment and the object being measured to prevent misalignment between the multiple encoded and phase patterns, which could lead to reconstruction errors.

Typical 3D scanning devices that apply fringe projection technology are known as snapshot 3D scanners (also referred to as photographic 3D scanners). Due to the significant size, weight, heat generation, low light efficiency, and shallow depth of field of the primary optical component (the DLP projector), these devices are mainly suitable for small to medium-sized objects, especially those with complex detail features (e.g., porous structures, latches, slots) and thin thicknesses, where multi-angle photography is not required. However, such devices have high requirements for natural environmental lighting and the color and material properties of the object being measured. Since DLP projectors operate as area light sources, the projected light onto the object’s surface is relatively weak; thus, the scanning effect is significantly influenced by ambient lighting conditions. There are also higher requirements for the color properties of the object’s surface; scanning dark-colored or reflective objects necessitates applying a powder coating on the object’s surface. Due to the need to project multiple frames of encoded and phase-shifted patterns during a single reconstruction process, the equipment cannot be moved, requiring a relatively stable shooting environment with poor shock resistance and less flexibility. For objects requiring multi-angle shooting, environments with vibrations, or large-scale scanning tasks, the efficiency is relatively low. Products from ZEISS GOM predominantly adopt this technological approach.

2. Advantages and disadvantages

(1) Advantages:

– High detail restoration: Raster stripes provide abundant texture information and achieve high-precision three-dimensional data acquisition, which is especially suitable for scanning objects with rich details such as sculptures.

– Diverse light source types: White light LED or blue light LED can be selected as the light source according to needs to adapt to different scenarios.

– No need for marking points splicing: Some raster scanning equipment has eliminated the need for point splicing. By optimizing the optical system and algorithm, large-scale, high-precision scanning can be performed, and the complete object model can be obtained through automatic splicing technology.

(2) Disadvantages:

– Large amount of data: Raster scanning generates large datasets, requiring high-performance computer hardware for processing.

– Scanning format and depth of field may be limited: Some devices may have limitations on format and depth of field, but advanced devices can increase the scanning range by adjusting the optical system.

– Poor material adaptability: The scanning effect on reflective and black objects is not good, and powder spraying may be required.

– Affected by ambient light: The scanning effect may not be good outdoors or in strong light environments.

3. Application scenarios

Suitable for fields with high precision requirements, such as art reproduction, mold manufacturing, etc. The advantage of not needing to attach marker points for splicing is particularly beneficial in scenarios with high requirements for comfort, such as human body scanningand artwork carvings.

Ⅱ. Laser Scanning: The perfect combination of high precision and wide application

1. Principle

Laser scanning technology is based on the principle of laser ranging. The laser is projected onto the surface of the object to be measured and the reflected laser is received. The scanner calculates the distance to the object based on this, determines the position of the object in space, and obtains three-dimensional point cloud data. This technology combines high precision and high fineness. For example, the industrial-grade laser 3D scannersprovided by Scantech: KSCAN-Magic compound 3D scannerand SIMSCAN-E intelligent wireless handheld 3D scanner, provide efficient data acquisition solutions for various industries. The iReal M3 3D scanner uses technology based on infrared parallel laser.

2. Advantages and Disadvantages

(1) Advantages:

– High precision: The basic accuracy of the iReal M3 3D scanner can reach up to 0.1mm, and the volume accuracy can reach up to 0.25mm/m, which can meet the 3D data acquisition needs of quasi-industrial scenarios. Scantech’s KSCAN-Magic compound 3D scanner and SIMSCAN-E intelligent wireless portable handheld 3d scanner both offer an accuracy of up to 0.02mm/m. These laser 3d scanners can be widely used in various fields to provide high-precision non-destructive testing solutions.

– High fineness: It can capture subtle surface features and present complex design details and delicate textures. Our iReal M3 3D scanner has a maximum resolution of 0.1mm, which can restore the geometric structure and angular details of objects in high definition, and can meet the scanning requirements of most customers for objects larger than 5cm.

– Good material adaptability: iReal M3 demonstrates excellent scanning results on reflective and black objects, often eliminating the need for powder spraying.

– High data integrity: It can scan blind spots and deep holes well to ensure the integrity of 3D data.

– Strong adaptability to ambient light: It supports outdoor scanning. iReal M3’s dual laser technology enables it to maintain stable scanning performance under various lighting conditions.

– Support color 3D data: Some laser scanners support color scanning, such as iReal M3 3D scanner.

(2) Disadvantages:

– Some devices need to be marked for splicing: When scanning large objects or performing complex scanning, some laser 3d scanners may need to stick points on objects or auxiliary tools to achieve splicing.

3. Application scenarios

Applicable to medical rehabilitation, art design, archaeological research, reverse engineering, 3D printing, scientific research and education and other fields.

Ⅲ. Speckle Scanning: the perfect combination of speed and large format

1. Principle

Speckle refers to a random distribution of point-like patterns that appear granular when a light source illuminates an object’s surface.

Speckle-based 3D scanning technology operates on the principle of binocular stereo vision, utilizing speckle feature blocks as matching primitives for 3D reconstruction. This technology primarily consists of two cameras and a speckle projector. The speckle projector can be a DLP projector containing speckle patterns, an LED projection lamp, or a specialized VCSEL (Vertical-Cavity Surface-Emitting Laser) speckle projector. The speckle projector casts the speckle pattern onto the object’s surface, and the left and right cameras use the similarity of block patterns along their respective epipolar lines. Through correlation calculations, they find the block with the highest matching degree to perform 3D reconstruction.

This technique allows for the simultaneous reconstruction of the 3D data of an object’s surface within the field of view and utilizes adjacent 3D point information to calculate the normal vector, curvature, and other 3D characteristics of the object’s surface within the field of view. Two consecutive frames of 3D data can be stitched, positioned, and accumulated using the characteristic data, enabling continuous 3D scanning.

2. Advantages and disadvantages

(1) Advantages:

– Fast scanning speed: suitable for scenarios where data is quickly acquired, such as human body scanning.

– Large format and depth of field: iReal 2E has a large scanning area of 580mm*550mm, a scanning distance range of 280-1000mm, and a large scanning depth of field of 720mm, which is convenient for scanning medium and large objects.

– Black and hair scanning ability: excellent performance in scanning matte black objects (including hair).

– Light color recognition ability: no need to manually adjust the exposure during scanning, making scanning smoother and easier to use.

– Supports dark scanning: no glare during scanning, more comfortable and safe, reduces resistance of the scanned person, and makes human body scanning easier to carry out.

– Supports scanning in dark environments: iReal 2E products perform clean body scanning in dark environments (such as when acquiring breast cancer/spinal correction data), which provides a better patient experience.

– Supports outdoor scanning: strong adaptability to light environments, such as iReal 2E and iReal M3 products support direct scanning in sunlight, meeting the scanning needs of multiple scenarios, such as outdoor archaeology, plant trunk scanning growth morphology analysis, etc.

– Usually no need for marking points scanning: the principle of speckle scanning technology determines that there is no need for point-by-point scanning or point splicing, and it has the advantage of no need for point splicing, making it particularly suitable for scenarios such as human body scanning and artwork carvings.

(2) Disadvantages:

– Relatively low detail restoration: The texture information in the scanning results is not rich enough, which is a common issue with speckle scanning technology.

– There are certain limitations on scanning reflective and black objects: in some special cases, powder spraying may still be required.

3. Application scenarios

Speckle scanning technology is widely used in large sculpture scanning, full body scanning and other fields.

Ⅳ. Comparison of Fringe Projection, Speckle Scanning and Laser Scanning

In summary, the three 3D scanning technologies of grating, laser and speckle have their own advantages. The selection of the appropriate technology needs to be determined according to the specific application scenario and needs. Understanding the characteristics and limitations of these technologies will help us better utilize them to promote the development of different fields.