Image processing device and image processing method

1. An image processing device for processing an input image so as to reproduce a halftone, comprising:

a matrix setting section for setting a threshold matrix having a plurality of elements arranged in M columns×N rows, at least two threshold values being stored in each of the elements;

an element specifying section for specifying an element of the threshold matrix that corresponds to a position of a pixel in the input image; and

a multilevel signal generating section for fetching the threshold values from the specified element and for generating a multilevel signal by transforming an input pixel value of the pixel to one of multiple levels in accordance with the fetched threshold values;

wherein the multilevel signal generating section: (i) outputs a constant value Doutmin as the multilevel signal when a first condition, that the input pixel value is smaller than or not larger than a minimum value of the threshold values, is satisfied; (ii) outputs a constant value Doutmax as the multilevel signal when a second condition, that the input pixel value is larger than or not smaller than a maximum value of the threshold values, is satisfied; and (iii) outputs an interpolation value that is between the two constant values Doutmin and Doutmax as the multilevel signal by carrying out a predetermined operation when both the first condition and the second condition are not satisfied.

2. The image processing device of claim 1 , wherein the predetermined operation is a linear interpolating operation using the threshold values.

3. The image processing device of claim 1 , wherein the threshold values are two threshold values UL(e) and LL(e) and the predetermined operation is a linear interpolating operation expressed by the equation:

D out H=D outmin+[ D in− LL ( e )]×( D outmax− D outmin)/[ UL ( e )− LL ( e )]

where:

DoutH is the interpolation value;

UL(e) is the maximum value of the threshold values;

LL(e) is the minimum value of the threshold values;

and

Din is the input pixel value.

4. The image processing device of claim 1 , wherein the multilevel signal generating section generates the multilevel signal taking one level from desired number of multiple levels.

5. The image processing device of claim 1 , wherein the multilevel signal generating section outputs a value between the two constant values Doutmin and Doutmax to transform the input pixel value to one of the multiple levels.

6. The image processing device of claim 1 , further comprising:

a dot shift signal generating section for generating a dot shift signal in accordance with the multilevel signal by carrying out a pattern matching process; and

a pulse signal generating section for generating a pulse signal in accordance with the multilevel signal and the dot shift signal.

7. An image processing method for processing an input image so as to reproduce a halftone, comprising:

setting a threshold matrix having a plurality of elements arranged in M columns×N rows, at least two threshold values being stored in each of the elements;

specifying an element of the threshold matrix corresponding to a position of a pixel in the input image; and

fetching the threshold values from the specified element and generating a multilevel signal by transforming an input pixel value of the pixel to one of multiple levels in accordance with the fetched threshold values;

wherein in the generating of the multilevel signal: (i) a constant value Doutmin is outputted as the multilevel signal when a first condition, that the input pixel value is smaller than or not larger than a minimum value of the threshold values, is satisfied; (ii) a constant value Doutmax is outputted as the multilevel signal when a second condition, that the input pixel value is larger than or not smaller than a maximum value of the threshold values, is satisfied; and (iii) an interpolation value between the two constant values Doutmin and Doutmax is outputted as the multilevel signal by carrying out a predetermined operation when both the first condition and the second condition are not satisfied.

8. The image processing method of claim 7 , wherein the predetermined operation is a linear interpolating operation using the threshold values.

9. The image processing method of claim 7 , wherein the threshold values are two threshold values UL(e) and LL(e) and the predetermined operation is a linear interpolating operation expressed by the equation:

D out H=D outmin+[ D in− LL ( e )]×( D outmax− D outmin)/[ UL ( e )− LL ( e )]

where:

DoutH is the interpolation value;

UL(e) is the maximum value of the threshold values;

LL(e) is the minimum value of the threshold values;

and

Din is the input pixel value.

10. The image processing method of claim 7 , wherein in the generating of the multilevel signal, the multilevel signal taking one level from desired number of multiple levels is generated.

11. The image processing method of claim 7 , wherein in the generating of the multilevel signal, a value between the two constant values Doutmin and Doutmax is outputted to transform the input pixel value to one of the multiple levels.

12. The image processing method of claim 7 , further comprising:

generating a dot shift signal in accordance with the multilevel signal by carrying out a pattern matching process; and

generating a pulse signal in accordance with the multilevel signal and the dot shift signal.