Hybrid Compression Scheme for Scanned Documents

Abstract—Compression is used to reduce the irrelevant or redundant data, in order to save space or transmission time. Scanned document is compressed to reduce the requirement of the storage space and bandwidth. This paper proposes, a hybrid coding method for scanned documents. This hybrid codec includes a lossy block based compression scheme called Absolute Moment Block Truncation Coding (AMBTC), a block based pattern matching and a lifting based discrete wavelet transform. AMBTC encoder outputs a bitmap and two mean values for each block. For greyscale document images bitmap contains most of the information. A bitmap interpolation and a lossless block matching scheme is applied on bit map to reduce its size. The higher and lower mean sub images from the AMBTC encoder is coded separately by DWT. The proposed method combines both the advantages of AMBTC and DWT. It performs a higher compression with high quality reconstructed versions. The proposed work is analysed by Peak Signal to Noise Ratio (PSNR) and compression ratio (CR). The result reveals that, proposed method shows high PSNR and high compression ratio. Keywords—AMBTC, DWT, Scanned Document Compression, Block based pattern matching