User Manual - pancroma

57. Image Processing Utilities – Panchromatic Images________________________________________________________________Before the advent of PANCROMA TM automatic image processing algorithms,intensive image processing efforts were often necessary to achieve accurate andpleasing pan sharpened images. PANCROMA TM automatic preprocessingalgorithms are often sufficient to produce excellent results without any manualintervention. However all of the manual utilities are still available if needed.PANCROMA TM provides a toolkit of image processing utilities that allows manualproduction of high fidelity of the pan-sharpened images.The following utilities are enabled when pan sharpening images. Note: several ofthese utilities have been overcome by development of the histogram match,ENHG and XIONG algorithms. They remain available for manual processing orfor adjusting automatically corrected images if desired.Snow and Sand Glare Reduction Group Utility (Grayscale; RGB; Pan)Sometimes areas of an image are close to saturation as a result of intensereflection from snow, sand or clouds. This utility uses a combination of twosliders (which is a common format for many PANCROMA TM image processingutilities). The upper slider selects the clipping threshold. That is all pixels abovethe setting on the slider bar will be affected by the clipping operation. Forexample if the slider is set at 245, then all pixel values of 245 and above will beadjusted.IMPORTANT NOTE: Since all Landsat files have 8 bits of color information, thecolor level can range from 0 – 255 i.e. 256 total levels.The lower slider bar sets the adjustment value, in this case the number by whichall the values above the clipping threshold will be decremented. The result is thatpixel values that are so “overexposed” so that detail is lost can be made lessintense so that detail can be recovered.This utility can be useful when processing snow capped peaks using the ELINprocessor as abrupt changes in brightness can cause ringing with this algorithm.Change Dark PixelsAs previously described, one of the problems inherent to the unenhanced HSIand Brovey algorithms used by PANCROMA is that the blue ocean color can belost. This often results in ocean areas turning out with a dark greenish cast oreven just black. In order to correct this, PANCROMA TM has a simple andeffective algorithm that adds a specified value to the ‘blue’ channel of all RGBpixels with values below the selected threshold. Thus if your test panchromatic162