| 摘要 |
A halftone cell is composed of a plurality of pixel groupings predefined to correspond to optimal tone level gradations. Selected output pixel groupings vary in number, and in shape of subpixels used from other pixel groupings, in order that successive input levels correspond to successive halftone cells defining substantially equal changes in a measured darkness value. Tone level gradations are optimized by purposeful correlation of input levels to output levels, especially where the number of output levels exceeds the number of input levels. During optimization, a calibration sample is produced by the image output device and calibration elements are empirically measured. Darkness change between successive levels is calculated and compared. Where the percentage of darkness change exceeds a desired amount, additional calibration elements are produced until the change calculated between successive levels is substantially the same. Successive input levels are associated with successive output levels such that a change between any adjacent input levels produces a change in darkness in the desired amount. The correlation is stored in a look up table for use during operation of the image output device.
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