Method and device for generating threshold matrix for determining state of formation of dots composing output image, quantizer comprising threshold matrix for generating output image data, and image forming device and storage device comprising threshold matrix

摘要

A threshold matrix generating method includes: generating q(x, y, g) in which the number of dots in an initial dot pattern is varied; calculating an error matrix (ERR(x, y, g)) of q(x, y, g); calculating AVE(a, b) representing the uniformity of the number of dots in discrete blocks into which the dot pattern has been divided; determining two pixels, of which the dot positions are to be swapped, on the basis of ERR (x, y, g) and AVE(a, b); swapping the dot positions; calculating the evaluation value (MSE(n)) of q(x, y, g) after the positional swapping; and repeating the positional switch of the dots repeating the generation of q(x, y, g) and the positional swapping of the dots with q(x, y, g) functioning as the initial dot pattern until a q(x, y, g) satisfying MSN(n)

主权项

1. A method of generating a threshold matrix used for determining a state of formation of a plurality of dots composing an output image, the method comprising the steps of:
generating a new dot pattern as a second dot pattern obtained by increasing or decreasing the number of dots of a first dot pattern having a predetermined number of dots in an pixel area of a predetermined size; rearranging the dots contained in the second dot pattern to obtain a third dot pattern having the dots rearranged therein; and repeating the generating of the new dot pattern while redefining the third dot pattern as the first dot pattern and the rearranging until a dot pattern having the number of dots based on a desired dot ratio is obtained; wherein the rearranging further includes: a dot pattern evaluation value calculating process calculating a dot pattern evaluation value based on a difference between the second dot pattern and a dot pattern obtained by subjecting the second dot pattern to a predetermined filtering aimed at implementing a desired spatial frequency, in a manner corresponding to each location in the threshold matrix; a first uniformity evaluation value calculating process calculating a first uniformity evaluation value each representing uniformity of the number of dots of first discrete blocks obtained by dividing the pixel area of a predetermined size; a dot rearrangement location determining process determining new locations of placement of dots and locations of deletion of dots in the process of rearrangement of dots, based on the dot pattern evaluation value and the first uniformity evaluation value; a rearrangement pattern generating process rearranging the dots of the third dot pattern, based on the new locations of placement of dots and the locations of deletion of dots determined in the rearrangement location determining process; a dot dispersion evaluation value calculating process calculating a dot dispersion evaluation value with respect to the rearranged third dot pattern; a rearrangement repetition determining process determining whether repetition of the dot pattern evaluation value calculating process, the first uniformity evaluation value calculating process, the dot rearrangement location determining process, the rearrangement pattern generating process and the dot dispersion evaluation value calculating process are performed or not, based on the dot dispersion evaluation value of the rearranged third dot pattern; and a process redefining the rearranged third dot pattern as the second dot pattern, if the repetition was determined in the rearrangement repetition determining process.