O(1) bilateral filtering with low memory usage

We propose a O(1) algorithm for bilateral filter with low memory usage. Bilateral filter can be converted into weighted histogram operation. Applying line buffers of column histograms, we can reduce the number of calculation needed to construct recursive center-weighted local histogram. Also our method have advantage in terms of memory requirements. We used a 2-GHz CPU with our method and achieved one million pixels per 0.5 sec operation and high PSNR over 40 dB without the need for temporary frame buffers or additional instructions (downsampling, SIMD instructions, or multi-thread operations).