Calculation of GR and GB color ratios in a local area uses a weighted average filter having weighting coefficients where the ratio of total sums of weighting coefficients for G and R pixels is 1:1, and weighted average filter having weighting coefficients where the ratio of total sum of weighting coefficients for G and B pixels is 1:1, respectively, on pixel lines in a horizontal direction and a vertical direction in a kernel. R and B pixel values are then calculated by interpolating the pixel value of a pixel to be processed with the G pixel value at the pixel position to be subjected to a demosaic process and the color ratio.