An efficient scheme for JPEG2000 progressive decoding is proposed, which is capable of handling image codestreams with SNR progressiveness. In order to avoid processing the same codestream data more than once when decoding SNR progressive images, a pair of techniques are introduced in our decoding scheme; reusing of intermediary decoded data and differential IDWT. Comprehensive evaluation of our scheme demonstrating that with 20% increase of required memory size, more than 40% of computational costs can be reduced in comparison with conventional (non-progressive) decoding scheme.