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High Resolution 3D Color Laser Scanner

The High Resolution 3D Color Laser Scanner has been used for scanning museum objects such as paintings, ethnographic and archaeological collections and natural history specimens. The maximum resolution configuration of this scanner is sufficient to record and examine fine brush stroke details on paintings, as well as tool marks on sculptures and archaeological objects.

One very important feature of using the auto-synchronized system in these applications is that relatively simple modifications can be made to enable simultaneous shape and color digitization. Due to the simultaneous position and amplitude digitizing of the three colors on the CCD (Charge Coupled Device) image sensors, the shape (x,y,z) data and the reflectance (R,G,B) data are recorded in perfect registration. This is a unique feature of this technology – particularly for recording important works of art.

On a commercial basis, Arius3D (http://www.arius3d.com) has an exclusive license for this technology from NRC.

Principle of operation:
In Figure 1, three laser wavelengths - red, green and blue (RGB) are used as the laser source. When superimposed in the scanning system, it results in the projection of a 50 to 100 micron diameter “white” laser spot on the object. In the detector, a color separation device such as a prism or a dispersive optical element is added near the lens to split the three RGB wavelengths reflected from the object on the CCD detector. The amplitudes of the three peaks are converted into reflectance values for the three wavelengths by a calibration process that takes into account the geometry of illumination and detection at each surface element. Due to the simultaneous position and amplitude digitizing of the three colors on the CCD, the shape (x,y,z) data and the reflectance (R,G,B) data are recorded in perfect registration.

Figure 1: The auto-synchronized scanning configuration. For simultaneous color and shape recording using the High Resolution 3D Color Laser Scanner, a polychromatic RGB laser source is used to project a “white” laser spot on the object. The triangulated light reflected from the object is separated into its three primary R,G and B wavelengths using a prism for recording by the CCD detector. This results in the simultaneous recording of the shape (x,y,z) coordinates and the reflectance (R,G,B) data in prefect registration.

In operation, the scanner (Figure 2a) is mounted on a stable three degree-of-freedom translation stage gantry (illustrated in Figure 2b), which is also equipped with a rotation table. Depending on the shape of the object, scans are made either by rotating the object on the rotation table or by scanning successive views using the translation stage. Each view is composed of 1024 profiles and each profile contains 1024 coordinates of x, y, z, R, G, B shape and reflectance data (Figure 2c). In order to digitize a complete object, a series of successive scans or overlapping images are recorded over the complete surface of the object. The scans are subsequently merged (Figure 2d), and a final archival quality 3D digital model of the object (Figure 2e) is produced.

To see the Data Acquisition of the Nicaraguan Sculpture, click on this link: nrc-3d-color-imaging-small.avi

Figure 2: Operation of the High Resolution 3D Color Laser Scanner
(a) The High Resolution 3D Color Laser Scanner shown scanning a figurine mounted on the rotation table. (b) Illustration of the three degree-of-freedom translation stage. (c) Front view of the figurine during scanning. The white line is a time exposure of the white laser spot during scanning of a profile. (d) Four images aligned with a different color associated with each image. (e) Side view of the final 3D digital model of the object.