ECW Compressor

The ER Mapper Enhanced Compression Wavelet (ECW) facility enables you to substantially reduce the file sizes of your images without any noticeable deterioration in quality.
The ER Mapper ECW Compressor uses wavelet compression technology which offers very good quality results at high compression rates. You can typically compress a color image to less than 2% to 5% of its original size (50:1 to 20:1 compression ratio) and compress a grayscale image to less than 5% to 10% of its original size (20:1 to 10:1 compression ratio).

This means that, at 20:1 compression, 500MB of color imagery will compress down to 25MB. You may actually achieve higher compression rates where your source image has a structure well suited to compression.