title: Low bit-rate image compression via adaptive down-sampling and constrained least squares upconversion.
abstract: Recently, many researchers started to challenge a long-standing practice of digital photography: oversampling followed by compression and pursuing more intelligent sparse sampling techniques. In this paper, we propose a practical approach of uniform down sampling in image space and yet making the sampling adaptive by spatially varying, directional low-pass prefiltering. The resulting down-sampled prefiltered image remains a conventional square sample grid, and, thus, it can be compressed and transmitted without any change to current image coding standards and systems. The decoder first decompresses the low-resolution image and then upconverts it to the original resolution in a constrained least squares restoration process, using a 2-D piecewise autoregressive model and the knowledge of directional low-pass prefiltering. The proposed compression approach of collaborative adaptive down-sampling and upconversion (CADU) outperforms JPEG 2000 in PSNR measure at low to medium bit rates and achieves superior visual quality, as well. The superior low bit-rate performance of the CADU approach seems to suggest that oversampling not only wastes hardware resources and energy, and it could be counterproductive to image quality given a tight bit budget.
authors.affiliation: Department of Electrical and Computer Engineering, McMaster Univeristy, ON, Canada. xwu@ece.mcmaster.ca
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wu
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Zhang
authors.forename: Xiaohan
authors.initials: X
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D003195:Computer Communication Networks; D044962:Data Compression / Q000379:methods*; D003627:Data Interpretation, Statistical; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D038622:Internationality; D016018:Least-Squares Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014741:Video Recording / Q000379:methods* / Q000592:standards