Method and apparatus for correcting unadjusted threshold arrays for halftoning by use of parameterized transfer functions that generate adjusted threshold arrays at run time

摘要

A printer that stores a minimal number of unadjusted stochastic threshold arrays in non-volatile memory, in which the unadjusted threshold arrays are used to generate adjusted threshold arrays at run time by use of special parameterized transfer functions. The unadjusted array for a particular color is stored in the printer's ROM and preferably is stored in a packed configuration to save memory space. The parameterized transfer functions are used to convert the unadjusted threshold data into adjusted threshold data for each color and type of print media. These parameterized transfer functions are stored in the printer's non-volatile memory, and take up very little memory space. In a preferred embodiment, the unadjusted threshold array comprises a 128 row by 128 column sized array, and each element of this array comprises a 10-bit number. When a parameterized transfer function is applied to this unadjusted array, the resulting numeric values for the adjusted array elements are produced as 8-bit numeric values. The greater precision in the originating unadjusted array provides more perceptual levels of intensity (i.e., color brightness), which is particularly important at the lighter shades of each color. The adjusted threshold arrays add only the number of dots per gray level (i.e., per differential threshold array level) that are required to provide a printer response that very nearly approximates the human eye perceptual differential response of intensity.