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Recently, selective encoding of scan slices is proposed to compress test data. This encoding technique, unlike many other compression techniques encoding all the bits, only encodes the target-symbol by specifying single bit index and copying group data. In this paper, we propose an extended selective encoding which presents two new techniques: flexible grouping strategy, X bits exploitation and filling strategy. Flexible grouping strategy is able to decrease the number of encoded groups to improve compression ratio. X bits exploitation and filling strategy can exploit a large number of don't care bits to reduce testing power with no compression ratio loss. Experimental results show that the proposed technique needs less test data storage volume and reduces average weighted switching activity by 24.7%, peak weighted switching activity by 11.6% during scan shift compared to selective encoding.