Fast LOT with unequal length basis functions: Realization and application in subband image coding

In this paper, the Lapped Orthogonal Transform (LOT) with unequal length ba sis function is considered. The proposed unequal length LOT (ULLOT) has bot h long basis of length 2M and short basis of length M, while the lengths of all bases of the conventional LOT are 2M. A new class of LOT can be constr ucted with some modifications of Malvar's Fast LOT. Therefore, the fast alg orithm for the Discrete Cosine Transform (DCT) will surely facilitate the c omputation of the ULLOT. Although the computational complexity of the ULLOT is always lower than that of the LOT, there exist some cases where the cod ing gain of the ULLOT becomes slightly higher than that of the LOT. Its abi lity to reduce ringing artifacts is an attractive feature as well. The size -limited structure for the finite length signal is investigated and the ULL OTs are tested on image coding application. The simulation results confirm the validity of the proposed ULLOT.