User Manual - pancroma

67. Tutorial - Pan Sharpening Full Size Landsat Files________________________________________________________________While many times you may only be interested in pan sharpening a portion of aLandsat image, some users will want to process full Landsat files. This is asizeable task as it involves processing about 600MB of input files and producingan RGB output file of up to 850MB. Computers with over 3GB of SDRAM cantypically process full sized Landsat files without any problem in as little as 225seconds. Computers with less RAM, slower processors and less capablegraphics cards may be challenged. The problem is not so much the processingspeed as the RAM required to display the color pan sharpened image.Large Landsat file sets can be processed the same as smaller files with a coupleof important notes:• It may not be possible to save full sized pan sharpened Landsat files inJPEG format. Currently the JPEG writer that PANCROMA TM uses is notvery memory efficient. Attempting to save pan sharpened Landsat fileswill result in an ‘Out of System Resources’ error message. Pansharpened SPOT images can be saved in JPEG format without anyproblem.• Files can be saved in BMP or PNG format. PNG format is recommendedas it employs a lossless compression algorithm and results in files that are25% of the size of BMP files. The PNG writer is very memory-useefficient.• Processing the files can take a while. Processing speed is dependent onthe amount of RAM on your computer and your processor speed and type.In normal operation PANCROMA TM computes a bitmap display object from whichthe screen display is computed. Normally the graphics file that is stored to diskwhen any of the ‘Save’ menu items are selected is also extracted from the bitmapobject. However, a full sized color pan sharpened Landsat image can require750MB of RAM itself. The JPEG save utility requires another 750MB. Thiscombined with the executable, processing overhead, and other processesrunning on your computer can exceed the address space limitation imposed bythe Windows operating system and may generate an ‘Out of Memory’ errormessage.In order to avoid this, and to allow computers with fewer resources to process fullsize files, PANCROMA TM offers the option to forego displaying the image. Dothis by unchecking the ‘Display Pan sharpened Image’ checkbox on the PanSharpen Form that displays after you select the ‘Pan Sharpening’ menu item.This will prevent the program from attempting to display the image and willinvoke lightweight .bmp, .jpg and .png writers. You will be able to save the imageand then subsequently load it for viewing after the save.318