Why has the imagery from the Imagery Extraction Tool been compressed?
When working with imagery, including orthoimagery and satellite imagery, the size of image files can become very large. Compression of imagery not only reduces image file size, but also allows for faster access and easier distribution. For example, the Oregon 2005 half-meter imagery is approximately 4.1 terabytes in total size. Without compression, you would not be able to access this high-resolution imagery while panning and zooming in real time.The ER Mapper wavelet based compression technology results in manageable file sizes without a significant loss of image quality (Earth Resource Mapping Pty Ltd, 2001). ER Mapper Compressed Wavelet (ECW) v2.0 compression at a 9:1 ratio is at a low enough compression ratio where the “lost” data usually is not visually noticeable. Although keep in mind that visually lossless compression is not a mathematical guarantee but a subjective term. For more information on ER Mapper Compressed Wavelet (ECW) compression, please refer tothis publication:Ear
