Introduction An image isatwo-dimensionalsignalwhoseintensityatanypointisafunctionoftwospatial variables[4].Wenote x and y thespatialcoordinatesand f (x,y) theimageintensityvalues. Examples: photographs,stillvideoimages,radarimages,etc. An imagesequence (e.g.television)isthree-dimensionalsignalsincetheimageintensityat anypointisafunctionofthetwospatialonesandthetime. Eachpictureelementor pixel representsacertainphysicalquantity.Forinstance,aphotograph representstheluminancesofvariousobjectsasseenbythecamera.Butaninfraredimage collectsthetemperatureprofilevaluesofascene. Imageenhancement techniquesemphasizespecificimagefeaturestoimprovethevisualper- ceptionofanimage.