Method and apparatus for generating halftone image considering spatial frequencies of original image

摘要

The present invention is to generate a binary halftone image by taking full advantage of high resolution dots and low resolution dots. A Laplacian filter is applied to the density data of an original image to determine filtered density data representing spatial frequencies of the original image. A dot selection signal SEL for selecting one of the high resolution dots and the low resolution dots is generated based on a comparison between the filtered density data and a threshold data. A dot generator 32 includes a first SPM 48 for storing a threshold pattern of the low resolution dots and a second SPM 50 for storing a threshold pattern of the high resolution dots. A selector 52 receives threshold data DTH1 and DTH2 output from the first and the second SPMs 48 and 50 and selects one of the threshold data DTH1 and DTH2 in response to the dot selection signal SEL. A comparator 54 compares image data DIM with the selected threshold data and generates a dot signal Sd to record a binary halftone image.