Studies that utilize astronaut-acquired orbital photographs for visual or digital classification require high-quality data to ensure accuracy. The majority of images available must be scanned from film and electronically transferred to scientific users. This study examined the effect of scanning spatial resolution (1200, 2400 pixels per inch (21.2 and 10.6 µm/pixel)), scanning density range option (Auto, Full) and compression ratio (non-lossy: Tagged-Image File Format (TIFF); and lossy: Joint Photographic Experts Group (JPEG) 10:1, 46:1, 83:1) on digital classification results of an orbital photograph from the National Aeronautics and Space Administration (NASA)-Johnson Space Center archive. Qualitative results suggested that 1200 ppi was acceptable for visual interpretative uses for major land cover types. Moreover, Auto scanning density range was superior to Full density range. Quantitative assessment of the processing steps indicated that, while 2400 ppi scanning spatial resolution resulted in more classified polygons as well as a substantially greater proportion of polygons ≤0.2 ha, overall agreement between 1200 ppi and 2400 ppi was quite high. JPEG compression up to approximately 46:1 also did not appear to have a major impact on quantitative classification characteristics. We conclude that both 1200 and 2400 ppi scanning resolutions are acceptable options for this level of land cover classification, as well as a compression ratio at or below approximately 46:1. Auto range density should always be used during scanning because it acquires more of the information from the film. The particular combination of scanning spatial resolution and compression level will require a case-by-case decision and will depend upon memory capabilities, analytical objectives and the spatial properties of the objects in the image.
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Document Type: Research Article
School of Environment, Resources and Development Asian Institute of Technology P.O. Box 4 Klong Luang Pathumthani 12120 Thailand
Earth Sciences & Image Analysis Laboratory NASA-Johnson Space Center, Lockheed Martin Space Operations 2400 NASA Road 1, C23 Houston TX 77058-3799 USA
February 1, 2004
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