Abstract
The discrete cosine transforms (DCTs) have found wide applications in image/video compression (image coding). DCT-based lapped transforms (LTs), called fast LTs (FLTs), overcome blocking artifacts generated at low bit rate image coding by DCT while keeping fast implementation. This paper presents a realization of more effective integer FLT (IntFLT) for lossy-to-lossless image coding, which is unified lossless and lossy image coding, than the conventional IntFLTs. It is composed of few operations and direct application of DCTs to lifting blocks, called direct-lifting of DCTs. Since the direct-lifting can reuse any existing software/hardware for DCTs, the proposed IntFLTs have a great potential for fast implementation which is dependent on the architecture design and DCT algorithms. Furthermore, the proposed IntFLTs do not need any side information unlike integer DCT (IntDCT) based on direct-lifting as our previous work. Moreover, they can be easily extended to larger size which is recently required as in DCT for the standard H.26x series. As a result, the proposed method shows better lossy-to-lossless image coding than the conventional IntFLTs.
Highlights
The most popular image/video compression standards, JPEG [1,2] and H.26x series [3,4], employ discrete cosine transform (DCT) [5] at their transformation stages
5 Conclusions This paper presented integer fast lapped transforms (IntFLTs) for effective lossy-to-lossless image coding, which were constructed by few operations and direct-lifting of discrete cosine transforms (DCTs)
Many rounding operations and keeping small lifting coefficients by use of direct-lifting, the proposed IntFLTs performed better coding than the conventional IntFLTs in lossy-tolossless image coding
Summary
The most popular image/video compression (image coding) standards, JPEG [1,2] and H.26x series [3,4], employ discrete cosine transform (DCT) [5] at their transformation stages. JPEG 2000 [13] employs 9/7-tap and 5/3-tap discrete wavelet transforms (9/7-DWT and 5/3-DWT) for lossy and lossless modes, respectively [14]. This paper presents a realization of integer FLT (IntFLT), which is constructed by lifting structures with rounding operations, for lossy-to-lossless image coding. FLT can be applied to lossy-to-lossless image coding by simple lifting factorizations of rotation matrices and scaling factors, the obtained integer transform is unsuitable due to large rounding error because of many rounding operations. The proposed IntFLTs do not need any side information unlike IntDCT based on directlifting as our previous work [35] They can be extended to larger size which is recently required as in DCT for H.26x series. The proposed method shows better lossy-to-lossless image coding than the conventional IntFLTs
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