1. A method for adjusting a skin color of a digital image, adapted to adjust the skin color of an input image, the method comprising: loading the input image; performing a skin color detection process on the input image to generate a skin-color probability plot Sp in a size corresponding to the input image; providing a hue-saturation lookup table named LUT_Color; performing a skin color reproduction process on the input image to look up the LUT_Color for a chrominance pixel value of a corresponding color for each pixel value of the input image to generate a first image, and adjust each pixel value of the first image by using the skin-color probability plot Sp to generate a second image; performing a skin color smoothing process on the second image to generate a third image; and performing an image mixing process to mix pixel values of the input image and the third image at a corresponding mixing ratio to generate a target image.