Improve DCT Block Coder Performance by using Adaptive Downsampling and Interpolation at Low Bit Rates

We can improve image compression by downsampling the image prior to encoding process and estimated the missing portion after decoding at low bit rates. This paper presents a new algorithm in which, based on the adaptive decision of appropriate downsampling ratios, quantization steps and interpolation we can achieve high quality of coding by consideration of local visual significance at low bit rates and it acts as a conventional JPEG compression at high bit rates. The full resolution image can be restored from the DCT coefficients of the downsampled pixels followed by interpolation scheme at the decoder. The experiments have demonstrated better PSNR improvement over the existing techniques before the critical bit rate. In addition, the adaptive mode decision not only makes the critical bit rate less image-independent, but also automates the switching coders in variable bit-rate applications, since the algorithm turns to the standard JPEG method whenever it is necessary at higher bit rates.