Method and system for automated convergence and focus verification of projected images

Abstract

A method and system that objectively measures the convergence and focus of a 2 or 3 spatial light modulator (SLM) projection display. The system uses five (5) CCD cameras and a frame grabber to store red, green, and blue (R-G-B) data from selected pixels located in the corners and center of the projector's field-of-view. The horizontal and vertical locations for the R-G-B pixels at each of the five locations is determined and the delta (□) displacement of the green and blue pixels, relative to the reference red pixel, is calculated and used to converge the image. The optical focus of the system is also determined using a Fast Fourier Transform (FFT). The FFT is performed on this same data and a power spectrum summation beyond the first minima is determined. The focus is then adjusted to maximize this value.

1 . A method for convergence of an image projected by at least two modulators, the method comprising: 
 turning on a test pixel in the projected image;    capturing a combined image of the test pixel;    separating the combined image into a separate image for each of the modulators;    determining a centroid of x and y pulses representing the test pixel's width and height for each of the separate images;    calculating a convergence misalignment of the separate images based on a difference in x and y position between the centroids; and    mechanically aligning the modulators based on the convergence misalignment.    
   
   
       2 . The method of  claim 1  wherein the projected image is generated by at least three spatial light modulators.  
   
   
       3 . The method of  claim 2  wherein the spatial light modulators are micromirror devices.  
   
   
       4 . The method of  claim 3  wherein there are three micromirror devices projecting a red image, a green image, and a blue image as the separate images.  
   
   
       5 . The method of  claim 4 , wherein the mechanically aligning the modulators further comprises adjusting the micromirror devices projecting the green and blue images to align with the micromirror device projecting the red image.  
   
   
       6 . The method of  claim 1  wherein the capturing the combined image further comprises: 
 capturing a first image near a center of the projected image; and    capturing at least four additional images near a perimeter of the projected image.    
   
   
       7 . The method of  claim 1  wherein the capturing the combined image further comprises: 
 taking multiple scans in both horizontal and vertical directions across the test pixel; and    averaging the multiple scans to generate the combined image.    
   
   
       8 . The method of  claim 7 , wherein the taking the multiple scans comprises taking up to 20 scans.  
   
   
       9 . The method of  claim 1 , wherein the determining the centroids further comprises normalizing the height of the x and y pulses for each of the separate images.  
   
   
       10 . The method of  claim 9  wherein the determining the centroids further comprises measuring the test pixel width at a 90% level of the normalized height of the x and y pulses for each of the separated images.  
   
   
       11 . The method of  claim 10 , wherein the determining and measuring further comprise, for each of the centroids: 
 locating 90% levels for the x pulse's leading and trailing edges;    locating 90% levels for the y pulse's leading and trailing edges; and    setting the centroid as an intersection of a mid-point between the 90% levels of the x pulse's leading and trailing edges and a mid-point between the 90% levels of the y pulse's leading and trailing edges.    
   
   
       12 . The method of  claim 9 , wherein the determining the centroids further comprises, for both the x and y pulses for each of the separate images: 
 locating a first location that is greater than a first threshold on a leading edge of the normalized pulse;    locating a second location that is lower than a second threshold on a trailing edge of the normalized pulse;    locating a third location that exceeds a third threshold on the trailing edge of the normalized pulse, wherein the third location is between the first and second locations; and    averaging the first and third locations.    
   
   
       13 . The method of  claim 12 , wherein the locating the third location is performed after the locating the second location.  
   
   
       14 . The method of  claim 12 , wherein the first and third thresholds are 90% of the normalized height of the pulse, and the second threshold is 10% of the normalized height of the pulse.  
   
   
       15 . The method of  claim 1 , wherein the combined image is a 24-bit image, and wherein each of the separate images is an 8-bit image.  
   
   
       16 . The method of  claim 1 , wherein the mechanically aligning the modulators is performed automatically using fly-in-place robotics.  
   
   
       17 . The method of  claim 1 , wherein the mechanically aligning the modulators is performed manually.  
   
   
       18 . The method of  claim 1 , wherein the captured combined image and the separated images are magnified from the projected image.  
   
   
       19 . An apparatus comprising: 
 an image capture device for capturing a combined image of a test pixel projected by at least two modulators; and    a processor coupled to the image capture device for receiving the captured combined image, the processor configured to 
 separate the combined image into a separate image for each of the modulators,  
 determine a centroid of x and y pulses representing the test pixel's width and height for each of the separate images,  
 calculate a convergence misalignment of the separate images based on a difference in x and y position between the centroids, and  
 provide data to mechanically align the modulators based on the convergence misalignment.  
   
   
   
       20 . The apparatus of  claim 19 , wherein the processor is configured to automatically align the modulators.