User Manual - pancroma

70. Tutorial – Gap Filling using Hayes Method________________________________________________________________The third PANCROMA TM method for filling gaps in Landsat ETM+ images is theHayes Interpolation method. This procedure uses a computational approach tosolving the gap filling problem. Instead of directly substituting the missing pixelsfrom the Adjust image into the Reference image, it computes the brightness levelof each missing pixel in the Reference image using information on correspondingpixels in the Adjust image.Like the Transfer method, the Hayes method also requires exactly matchedReference and Adjust images. The procedure for producing them is exactly thesame as described in the previous Tutorials, using either the semi-automatic orfully automatic methods for co-registering your two sets of three Landsat bandfiles.After you produce the matched images the gap filling procedure is similar with afew important differences. You start the filling procedure by opening first theReference (grayscale) image (the one with the gaps), followed by the Adjustimage.When the images are loaded, select ‘Gap Fill’ | ‘Gap Fill Hayes Method’. A GapFill Data Form will appear. You can select the algorithm parameters: SearchExtents, the Gap Threshold and the Comparison Radius. The default values are20, 4 and 4, respectively.The Search Extents defines the size of the sliding window within whichPANCROMA TM will look for similar pixels. PANCROMA TM will search the target+/- the Search Extents, so the size of the window is twice the Search Extentsvalue.The Comparison Radius value determines how closely a searched pixel must beto the target pixel in order to be considered ‘similar’. The default value is 4,meaning that pixels within 4 levels of the target will be considered similar. Forexample, if the target has value 83 and the Threshold is 4, then coordinates ofpixels with values 79, 80, 81, 82, 83, 84, 85, 86 and 87 will be considered assimilar for purposes of the computation.The Gap Threshold determines which pixels in the Reference image will becomputed. Any pixel with a brightness value less than the Gap Threshold will beconsidered a missing pixel and PANCROMA TM will attempt to fill it. After youselect your values, the program will compute the gap filled image. Note that ahistogram match will not be computed for the Hayes method, as it does notgenerally benefit the result.330