Low bit-rate image compression via adaptive down-sampling and constrained least squares upconversion

  • Authors:

  • Xiaolin Wu;Xiangjun Zhang;Xiaohan Wang

  • Affiliations:

  • Department of Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada;Department of Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada;Department of Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada

  • Venue:
  • IEEE Transactions on Image Processing
  • Year:
  • 2009

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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.