Due　to　the　uneven　distribution　of　light　at　night,　the　quality　of　night　color　image　is　usually　poor,　such　as　low　image　contrast,　low　brightness　and　less　texture.　Most　of　existing　night　color　image　enhancement　algorithms　can＇t　preserve　the　details　and　eliminate　the　＇halo　effect＇　at　the　edge　areas　of　high　contrast　in　the　nighttime　image　processing.　To　solve　these　problems,　we　propose　an　image　enhancement　algorithm　based　on　purposeful　optimization　and　improved　histogram　equalization.　The　process　of　the　algorithm　is　conducted　in　the　luminance　channel　of　the　HSV　color　space:　1)enhance　the　contrast　of　the　source　image　and　reserve　details　furthest　through　improving　the　image　gradient　values　using　the　method　of　optimization;　2)enhance　the　image　by　the　improved　histogram　equalization　which　increases　the　probability　of　pixel　values　of　small　probability;　3)enhance　the　image　brightness　through　gamma　correction.　Subjective　and　objective　evaluation　shows　that　our　algorithm　greatly　enhances　the　image　contrast　and　brightness,　recovers　the　image　details,　and　eliminates　the　＇halo　effect＇　efficiently.　Experiments　on　the　different　nighttime　images　demonstrate　the　effectiveness　of　our　approach.　In　summary,　our　algorithm　is　effective　to　complete　the　challenging　task　of　enhancing　the　nighttime　image.　©,　2015,　Science　Press.　All　right　reserved.