an image processing method and its associated image processing circuit for processing an image based on a sequential couleur avec memoire system are provided . the image includes a first pixel , a second pixel and a third pixel , which are successively arranged in a same vertical line and are respectively corresponding to a first image signal and a second image signal and a third image signal . the image processing method includes steps of calculating a chroma signal via a vertical filtering process according to the first image signal , the second image signal and the third image signal ; calculating a chroma angular frequency via a frequency modulation process according to the chroma signal ; and generating a chromaticity according to the chroma angular frequency .