1. A pixel interpolation method comprising the steps of: (a) inputting a pixel signal of a predetermined color space; (b) calculating a chroma evaluation value of an area consisting of a specified pixel and its surrounding pixels; (c) selecting a correlation judgment method and a pixel interpolation method on said specified pixel on the basis of said chroma evaluation value; and (d) performing a pixel interpolation process on said specified pixel in a correlation direction determined by the selected correlation judgment method, by using the selected pixel interpolation method, wherein by using predetermined two threshold values TH 1 and TH 2 (TH 1 ≧TH 2 ), if said chroma evaluation value is not larger than the threshold value TH 2 , a correlation judgment method for gray image and a pixel interpolation method for gray image are selected, if said chroma evaluation value is larger than the threshold value TH 2 and not larger than the threshold value TH 1 , a correlation judgment method using a correlation value selected out of correlation values for gray image and color image and a pixel interpolation method for color image are selected, and if said chroma evaluation value is larger than the threshold value TH 1 , a correlation judgment method for color image and a pixel interpolation method for color image are selected in said step (c).