User Manual - pancroma

31. ELIN Local Optimization Algorithm_______________________________________________________________The ELIN algorithm is the latest PANCROMA TM technology designed atovercoming the problem of spectral distortions introduced by the nature of thepanchromatic bands that represent the high-resolution information in satellitedata scenes. As explained elsewhere in this manual, the Hue, Saturation,Intensity (HSI) transformation method provides a convenient way to inject highresolution spatial information into the lower resolution spectral information inorder to fuse the spatial and the spectral to produce a high resolution colorimage. The problem with the naive approach is that the process only works if thespectral characteristics of the panchromatic band closely match those of thediscarded Intensity band. Unfortunately, this may not be true. Landsat providesthe most common example of this type of panchromatic band.The Landsat panchromatic band is sensitive to light in the 0.52µ to 0.92µwavelength range. Visible light spans the 0.45µ to 0.69µ wavelength range. Asa result, substituting the panchromatic band for the Intensity band beforereverse-transforming back to red-green-blue (RGB) color space can causenoticeable and often severe spectral distortions in the resulting pan sharpenedimage, especially in areas of high Near Infrared (NIR) reflectivity like grasslandsand other narrow-leaf vegetation for example. The methods described in theprevious sections address this problem by using the NIR band 5 to adjust thepanchromatic band before substituting. These methods can produce veryacceptable results. However, none of them is perfect because while NIRadjustment can correct for panchromatic NIR sensitivity, it cannot provide themissing blue band (0.45µ-0.515µ) information.ELIN takes a different approach. This algorithm replaces the panchromatic bandwith a synthesized panchromatic (SPAN) band that has virtually zero spectraldistortion. When the SPAN band is substituted for the Intensity band, the reversetransformation from HSI color space to RGB color space occurs with a similarlack of spectral distortion. The result is often a pan sharpened image thatmatches the low resolution RGB image color tones almost exactly.The following set of images demonstrates the advantages of ELIN. The firstimage is a subset from a Landsat scene L71001086_08620051201_BXX.TIFRGB color composite image from band1, band2 and band 3. Immediately after itis the corresponding pan sharpened image using the HSI transform method.83