User Manual - pancroma

75. Tutorial - Manual Gap Fill Adjustment Procedure________________________________________________________________Although the histogram matching method is very effective, it is possible to effecta match between the Reference and Adjust images using purely manual means.This method can also be used to adjust images that have been histogrammatched, to hopefully produce better results. Manual methods can also be usedto improve the automatic result. The first step in this process is to load aReference and Adjust band. Check the ‘Activate Image Processing Routines’check box in the PANCROMA TM main window. Now select ‘Gap Fill | Gap FillETM+ from the menu.PANCROMA TM will present the ‘Image Processing Data Input’ box. Select the‘Enable Channel Level Adjust’; ‘Gap Fill Threshold’, ‘Apply Haze Reduction’,‘Apply Contrast Adjust and ‘Save Settings’IMPORTANT NOTE: Because the image matching process is iterative you willwant to save your settings between iterations co you can make changesincrementally.The ‘Channel Level Adjust’ slider is the integer value to be added or subtractedfrom each pixel in the ‘Adjust’ image. PANCROMA TM will transfer the value ofeach pixel in the ‘Adjust’ image to the corresponding pixel in the ‘Reference’image if the pixel value in the ‘Reference’ image is equal to or below the Gap FillThreshold value. For example, if the slider value is set at the default value of‘30’, then if any pixel value in the Reference image is 30 or less, it will bereplaced by the corresponding pixel value in the Adjust image. An adjustablethreshold is necessary because, unfortunately not all of the Reference image gappixel values are zero as you would expect. As a result of the Reference imagecharacteristics, gap values may be as high as 20 or 30.IMPORTANT NOTE: You may wish to use the ‘Compute Running Average’utility described below in order to aid in getting the best overall brightness match.IMPORTANT NOTE: An added complication is that the brightness of each of thethree Reference band files is not the same, so it may be necessary to adjust the‘Gap Fill Threshold’ to different values for each of the three band images. Youwill know if the ‘Gap Fill Threshold’ value is not set high enough if you see dark“speckles” inside the gaps, indicating that, for example a dark pixel with a valueof say, 24 did not get replaced because the ‘Gap Fill Threshold’ value was set at20.IMPORTANT NOTE: Setting the ‘Gap Fill Threshold’ value too high will causeunwanted substitution of valid pixels.349