Fig. 1. Bilateral filtering algorithm^［8］

Fig. 2. Range domain piecewise approximation.（a）Curve of similar values with ΔI for different σr；（b）Piecewise approximate at σr=75.

Fig. 3. Spatial kernel and piecewise approximate with different σr.（a）5×5 spatial kernel；（b）σr=15；（c）σr=30；（d）σr=45；（e）σr=60；（f）σr=75.

Fig. 4. Hardware architecture diagram of algorithm

Fig. 5. Vivado simulation result.（a）Data processing started；（b）Data processing completed.

Fig. 6. Variation of PSNR（a）and SSIM（b）with σr at different σ_n

Fig. 7. Comparison of filtering effect between MATLAB and FPGA.（a）Original images；（b）Noise images；（c）MATLAB processing；（d）FPGA processing；（e）~（h）Enlarged images.