User Manual - pancroma

Another reason to keep the Search Extents as small as possible is that the edgeof the window will eventually bump against the edge of the image. Since thetarget pixel is offset from the edge by the Search Extents, the result is that therewill exist a band of uncomputed pixels on each side of the image. If you areprocessing a Landsat scene, this will not matter much because this band will bein the collar area. If you are computing a subset image, however, this will resultin a “fringe” around the edges of the image.Your selection of a Comparison Radius value will also have an effect on theresulting image quality. Choosing a Comparison Radius of zero means that onlypixels that exactly match the target pixel will be included in the computation.However, this may mean that no matching pixels will be discovered within thesearch window. In this case, PANCROMA TM increases the size of the searchwindow and repeats the process up to two more times.Repeated failures to find any matching pixels will slow down the computation. Ifno match is found, then no gap fill is computed, resulting in a black pixel in theprocessed image. On the other hand, if the Comparison Radius is set too large,the computation will not be very discriminating. This will result in blurring withinthe filled gap and loss of detail.It is generally a good idea to create a set of small subset Reference and Adjustimages to be used for empirically determining the optimal settings beforeattempting to fill entire scenes. If you are able to crop out the image collarsentirely the processing speed will be increased significantly. This is often difficultwith Landsat scenes as the path direction is not aligned with true north so that alot of the useful image may be lost if all collar area is cropped.The main benefit of the Hayes method is potentially better results. Pixelbrightness levels are computed from the Reference image itself, rather thancopied from the Adjust image.Of course the same issues discussed with the Transfer method, i.e. snow,clouds, seasonal changes to vegetative cover will affect images produced by theinterpolation method, although the effect of the latter is greatly reduced. Someexamples of results using this method are shown below.332