All halftoning uses a high-frequency/low-frequency dichotomy. In photographic halftoning, the low-frequency attribute is a local area of the output image designated a halftone cell. Each equal-sized cell relates to a corresponding area (size and location) of the continuous-tone input image. Within each cell, the high-frequency attribute is a centered variable-sized halftone dot composed of ink or toner. The ratio of the inked area to the non-inked area of the output cell corresponds to the luminance or graylevel of the input cell. From a suitable distance, the human eye averages both the high-frequency apparent gray level approximated by the ratio within the cell and the low-frequency apparent changes in gray level between adjacent equally spaced cells and centered dots.
All halftoning uses a high-frequency/low-frequency dichotomy In photographic halftoning, the low-frequency attribute is a local area of the output image designated a halftone cell. Each equal-sized cell relates to a correspond.ing area (size and location) of the continuous-tone input image. Within each cell, the high-frequency attribute is a centered vari.able-sized halftone dot composed of ink or toner The ratio of the inked area to the non-inked area of the output cell corresponds to the luminance or graylevel .of the input cell. From a suitable distance, the human eye averages both the high-frequency apparent gray level approximated by the ratio within the cell and the low-frequency apparent changes in gray level between adjacent equally spaced cells and centered dots