Initial Matching

• index edges. Form the stereo index, a raster based indexing scheme that forms lists of short edge strings broken at epi-polar tangencies. This ensures that each sting will cross each raster only once in parallel camera coordinates. Edges must be rectified prior to this stage. The stereo matcher will then limit potential matches to those strings which cross corresponding epi-polar rasters. It is possible for the same edge string to be indexed through adjacent rasters of the index if the rectification process produces aliasing of the edge string.
• disp hist. Perform an initial coarse scaled disparity histogram (using a subset of edge data), from which a conservative lower disparity range is recovered for each image region. The default otherwise is to use the whole disparity range defined by the extent of both images.

  Histogram options are;

  Match    all mats  : let all matches contribute to the matching.
           abs or    : let only matches within the allowable range of
                       absolute orientations contribute to the histogram.
           orient    : let only matches within the allowable range of
                       absolute orientation and of the same contrast sign
                       contribute to the histogram.
           or+con    : let only matches within the allowable range of
                       absolute orientation and similar value of signed
                       contrast be included in the histogram.
  
  
  Parameters :  Low disp (lower limit of fractional image width disparity)
                Up disp  (upper limit)
  

• set matches. Form potential matches between short edge strings accessed through the stereo indices accociated with left and right images. Matches are sought over the default disparity range or that recovered by disp hist. At most one match is recoverd for each short edge string from the left image with respect to each overall edge string from the right (allowance is made for edge strings that meander across the same raster several times).

  Matching options are;

  Match    all mats  : construct all matches.
           abs or    : construct only those matches within the allowable 
                       range of absolute orientation.
           orient    : construct only matches within the allowable range
                       of absolute orientation and of the same sign of
                       contrast
           or+con    : construct nly matches within the allowable range
                       of absolute orientation and similar value of signed
                       contrast.
  
  Parameters :  Low disp (lower limit of fractional image width disparity)
                Up disp  (upper limit)
                Vert Disp (vertical raster disparity tolerated)