  Prior to encoding RGB full-color images or Bayer color filter array (CFA)
images, chroma subsampling is a necessary and crucial step at the server side.
In this paper, we first propose a flow diagram approach to analyze the
coordinate-inconsistency (CI) problem and the upsampling process-inconsistency
(UPI) problem existing in the traditional and state-of-the-art chroma
subsampling methods under the current coding environment. In addition, we
explain why the two problems degrade the quality of the reconstructed images.
Next, we propose a reduced codebook and re-interpolation (RCRI) approach to
solve the two problems for enhancing the quality of the reconstructed images.
Based on the testing RGB full-color images and Bayer CFA images, the
comprehensive experimental results demonstrated at least 1.4 dB and 2.4 dB
quality improvement effects, respectively, of our RCRI approach against the CI
and UPI problems for the traditional and state-of-the-art chroma subsampling
methods.
