Full control multilevel error diffusion

1. A method for processing a digitized continuous tone image for reproducing the image by a printing device, the image including a plurality of input pixels having pixel tone values, wherein for each input pixel the printing device renders a corresponding output pixel by printing a level out of a plurality of available levels defined by a combination of a dot size and dot density or an overlap of dot size and dot density, including a level for printing no dot, the method comprising the steps of:

a) defining for each of the available levels a levelsplit curve, each levelsplit curve defining over the range of input pixel tone values an average contribution of the level for rendering that input pixel tone value;

b) inputting a tone value of an input pixel of the image;

c) applying the levelsplit curves to the tone value for obtaining the average contributions for each of the available levels;

d) modifying the average contributions by adding to them diffused quantization errors obtained from a previous processing step to obtain modified average contributions;

e) calculating the sum of the modified average contributions;

f) if the sum does not exceed a threshold, selecting for the output pixel the level that corresponds to printing no dot;

g) if the sum does exceed the threshold, determining which of the modified average contributions has the greatest value, and selecting for the output pixel the corresponding level;

h) determining a quantization error between the modified average contributions and the contribution of the selected level;

i) diffusing the quantization error to the average contribution of at least one unprocessed input pixel;

j) printing the output pixels.

2. The method according to claim 1 , further comprising the step of:

reading the plurality of levelsplit curves from a file.

3. The method according to claim 1 , further comprising the step of:

inputting the plurality of levelsplit curves through a user interface.

4. The method according to claim 3 , wherein at least one levelsplit curve of a level defined by an overlap of combinations of dot size and dot density is zero.

5. A system for reproducing a digitized continuous tone image, the image including a plurality of input pixels having pixel tone values, wherein for each input pixel the printing device renders a corresponding output pixel by printing a level out of a plurality of available levels defined by a combination of a dot size and dot density or an overlap of dot size and dot density, the system comprising:

means for inputting a tone value of an input pixel of the image;

at least one table including a plurality of levelsplit curves for converting an input tone value into an average contribution for each available level;

an adder for adding to the average contributions diffused quantization errors obtained from a previous processing step to obtain modified average contributions;

an adder for calculating a sum of the modified average contributions;

a comparator for determining if the sum is smaller or larger than a threshold;

a quantizer for selecting the level that corresponds to a maximum average contribution if the sum is larger than the threshold, and for selecting a level that corresponds with no dot if the sum is smaller than the threshold;

a subtracter for determining a quantization error between the modified average contributions and the contribution of the selected level; and

a diffuser for diffusing the quantization error to the average contribution of at least one unprocessed input pixel.

6. A system according to claim 5 , further comprising a printer.

7. A system according to claim 6 , wherein the printer is an inkjet printer.

8. A computer readable medium storing a computer program, when the computer program is executed on a computer, the computer program performs a method for processing a digitized continuous tone image for reproducing the image by a printing device, the image including a plurality of input pixels having pixel tone values, wherein for each input pixel the printing device renders a corresponding output pixel by printing a level out of a plurality of available levels defined by a combination of a dot size and dot density or an overlap of dot size and dot density, including a level for printing no dot, the method comprising the steps of:

a) defining for each of the available levels a levelsplit curve, each levelsplit curve defining over the range of input pixel tone values an average contribution of the level for rendering that input pixel tone value;

b) inputting a tone value of an input pixel of the image;

c) applying the levelsplit curves to the tone value for obtaining average contributions for each of the available levels;

d) modifying the average contributions by adding to them diffused quantization errors obtained from a previous processing step to obtain modified average contributions;

e) calculating a sum of the modified average contributions;

f) if the sum does not exceed a threshold, selecting for the output pixel the level that corresponds to printing no dot;

g) if the sum does exceed the threshold, determining which of the modified average contributions has the greatest value, and selecting for the output pixel the corresponding level;

h) determining a quantization error between the modified average contributions and the contribution of the selected level; and

i) diffusing the quantization error to the average contribution of at least one unprocessed input pixel.

9. The computer readable medium according to claim 8 , wherein the method further comprises the step of:

reading the plurality of levelsplit curves from a file.

10. The computer readable medium according to claim 8 , wherein the method further comprises the step of:

inputting the plurality of levelsplit curves through a user interface.

11. The computer readable medium according to claim 8 , wherein the method further comprises the step of:

printing the output pixels.