Dynamic range of color camera images superimposed on scanned three-dimensional gray-scale images

Abstract

A laser scanner scans an object by measuring first and second angles with angle measuring devices, sending light onto an object and capturing the reflected light to determine a distances and gray-scale values to points on the object, capturing a sequence of color images with a color camera at different exposure times, determining 3D coordinates and gray-scale values to points on the object, determining from the sequence of color images an enhanced color image having a higher dynamic range than available from any single color image, and superimposing the enhanced color image on the 3D gray-scale image to obtain an enhanced 3D color image.

What is claimed is: 
     
         1 . A method for optically scanning and measuring an object with a laser scanner, the method comprising:
 providing the laser scanner having integral components that include a light emitter, a light receiver, a first angle measuring device, a second angle measuring device, a control and evaluation unit, and a color camera;   providing a color display;   measuring a first angle with the first angle measuring device;   measuring a second angle with the second angle measuring device;   emitting with the light emitter an emission light beam;   reflecting the emission light beam from the object to produce a reception light beam;   receiving with the light receiver the reception light beam and obtaining a first electrical signal in response;   determining with the control and evaluation unit distances to a plurality of measuring points on the object based at least in part on the first electrical signals for each of the plurality of measuring points and on a speed of light in air;   determining with the control and evaluation unit gray-scale values for the plurality of measuring points;   capturing with the color camera a sequence of color images while the color camera is fixed in space, each image of the sequence captured with a different exposure time and having an associated first dynamic range, the color images providing second electrical signals in response;   determining with the control and evaluation unit a three-dimensional (3D) gray-scale image based at least in part on the first angle, the second angle, the distances to and gray-scale values for the plurality of measuring points on the object;   determining with the control and evaluation unit an enhanced color image having an enhanced dynamic range, the enhanced dynamic range being higher than the any of the associated first dynamic ranges, the enhanced color image based at least in part on the second electrical signals;   determining with the control and evaluation unit an enhanced 3D color image by superimposing the enhanced color image on the 3D gray-scale image; and   displaying the enhanced 3D color image on the color display.   
     
     
         2 . The method of  claim 1 , further including a step of applying dynamic compression to the enhanced color image to obtain a reduced dynamic range selected to match properties of the color display. 
     
     
         3 . The method of  claim 1 , wherein in the step of providing the laser scanner, the laser scanner further includes a rotatable mirror, the rotatable mirror configured to rotate about the first angle. 
     
     
         4 . The method of  claim 3 , wherein in the step of providing the laser scanner, the rotatable mirror reflects light from the object into the color camera. 
     
     
         5 . The method of  claim 4 , further including a step of determining an average value of second electrical signals over a plurality of the first angles obtained in response to rotation of the rotatable mirror. 
     
     
         6 . The method of  claim 5 , wherein, in the step of capturing with the color camera a sequence of color images, the sequence of color images has a number of color images in the sequence, the number of color images based at least in part on the average value of the second electrical signals. 
     
     
         7 . The method of  claim 6 , wherein, in the step of capturing with the color camera a sequence of color images, the different exposure time of each image of the sequence is based at least in part on the average value of the second electrical signals.