A　method　is　proposed　that　improves　the　robustness　and　accuracy　of　optical　flow　estimation　in　real　complex　scenes.　The　method　overcomes　the　limitations　incurred　by　illumination　variations　using　a　combination　of　the　brightness　constancy　and　gradient　constancy.　In　addition,　the　method　improves　the　reliability　of　optical　flow　estimation　by　applying　both　a　bilateral　filter　and　penalty　function.　Furthermore,　it　improves　the　calculations　and　applicability　of　the　estimated　optical　flow　by　employing　a　dual　algorithm　and　coarse-to-fine　scheme.　We　verify　the　proposed　method　using　scenes　from　the　Middlebury　optical　flow　database　and　a　real　complex　scene.　The　results　show　that　the　proposed　method　is　robust　to　illumination　variations　and　improves　both　the　accuracy　of　the　optical　flow　estimation　and　the　ability　to　extract　target　edges.　(c)　2018　SPIE　and　IS&T