 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.