An encoder (300) selects (702, 1302, 1304,1306,1308) one or more subsets of spatially or temporally correlated transformed data coefficients, on the basis of the significance of each subset in representing the data. The encoder (300) and a complementary decoder (400) may be applied to wavelet transform encoded images (500). The encoder (300) may be implemented on a wireless to Internet gateway server (108), in order to reduce byte size of encoded images (500) sent through a wireless network (112), and reduce the amount of processing that must be performed by a wireless device (118) to decode an image or other data. The decoder (400) and/or encoder (300) may be implemented on the wireless device (118).