Tone dependent green-noise error diffusion method and printing device thereof

A printing apparatus 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 printing apparatus comprising:

• a first adder, comprising a first terminal and a second terminal, wherein the first terminal of the first adder receives a color level value of a first color of the specific pixel and the second terminal of the first adder receives an error diffusion value of the first color of the specific pixel, thereby generating a first modified color level value of the first color of the specific pixel;
• a second adder, comprising a first terminal and a second terminal, wherein the first terminal of the second adder receives the first modified color level value of the first color and the second terminal of the second adder receives a output feedback value which is fed back to the first color of the specific pixel, thereby generating a second modified color level value of the second color of the specific pixel;
• a threshold comparing apparatus, comprising a first terminal and a second terminal, wherein the first terminal of the threshold comparing apparatus receives the color level value of the first color of the specific pixel to generate a first threshold value and a second threshold value, the second terminal of the threshold comparing apparatus receives the second modified color level value of the first color, and the threshold comparing apparatus compares the second modified color level value with the first threshold value and the second threshold value of the first color to generate a two-level value of the first color of the specific pixel;
• a subtracter, comprising a first terminal and a second terminal, wherein the first terminal of the subtracter receives the first modified color level value of the first color of the specific pixel and the second terminal of the subtracter receives the two-level value of the first color of the specific pixel, thereby generating an error value of the first color of the specific pixel;
• an error diffusion apparatus, comprising a first terminal and a second terminal, wherein the first terminal of the error diffusion apparatus receives the color level value of the first color of the specific pixel to generate a first error diffusion weighting value and a second error diffusion weighting value, and the second terminal of the error diffusion apparatus receives the error value of the first color of the specific pixel to generate an error diffusion value of the first color of the specific pixel;
• and
• an output feedback apparatus, comprising a first terminal and a second terminal, wherein the first terminal of the output feedback apparatus receives the color level value of the first color of the specific pixel to generate a first output feedback weighting value and a second output feedback weighting value, and the second terminal of the output feedback apparatus receives the two-level value of the first color of the specific pixel to generate an output feedback value of the first color of the specific pixel.