im: 0~255 8bit grayscalae image;
cluster_center: a cell array with structure for the quality aware cluster center;
cluster_center[l] is the cluster centers at the lth quality level, and it has the following domain:
centroids: [Kxd double], K is the cluster number center at each quality level, d is the feature dimension.
quality: the quality for the lth level;
feature_fun: the function handle for the patches based feature computation;
blksize: patch size, the default value is 8;
step: the step between patches, large step with speedup the computation while maintain the same performance, the default step is 12;
Q: the predicted quality of the input image (im), range [0 1].