Patent ID: 8050517

Claim:
A method of modulating sub-channel pixels in a multi grayscale monochrome output apparatus that represents a high grayscale (M+K)-bit monochrome input image through low grayscale M-bit sub-channels, M and K being integers greater than or equal to 1, the method comprising: generating a plurality of mask patterns; selecting mask patterns for a plurality of sub-channels from the plurality of generated mask patterns; determining weighted values using the values of the selected mask patterns and data of K least significant bits of the input image; and calculating M-bit data of the plurality of sub-channels on the basis of the weighted values, wherein when the M-bit data of the plurality of sub-channels calculated in the calculating of the M-bit data are the same, the method further comprises: selecting two channels among the channels; and adding a predetermined positive number to the value of one channel, and subtracting a predetermined positive number from the value of the other channel.