1. A tone dependent green-noise error diffusion method, for processing a continuous-tone input image arranged as a two-dimensional matrix, a location of a specific pixel of the continuous-tone image being represented by (x, y), the specific pixel comprising a plurality of colors, the method comprising: generating a first output feedback weighting value and a second output feedback weighting value according to a color level value of a first color of the specific pixel; executing an output feedback operation to generate a modified color level value according to the first output feedback weighting value and the second output feedback weighting value of the specific pixel; generating a first threshold value and a second threshold value of the first color according to the color level value of the first color; determining an output two-level value of the first color according to the modified color level value of the first color, the first threshold value and the second threshold value; generating a first error diffusion weighting value and a second error diffusion weighting value of the first color according to the color level value of the first color of the specific pixel; and executing an error diffusion operation according to the output two-level value of the first color, the first error diffusion weighting value and the second error diffusion weighting value.