HP 8550 Service Manual - Page 213

Text identification (character edge detection) As shown in figure 101, the text identification block identifies the edges of characters according to the Gm signal of the G image signal. It compares the Gm signal of the pixel in question and multiple pixels adjacent to it detect the edge component; it then identifies whether the pixel in question is part of the edge of a character or not based on the size of the edge component and the distribution of edge components. When the copy module identifies it as part of an edge, it generates the MJ signal (text detection signal). The MJ signal, however, will suffer a delay of 12 lines in the test identification block, requiring that the Gm image signal be advanced by 12 lines in relation to the G' image signal. The copy module generates the Gm image signal ahead of time by 12 lines so that the MJ signal (text detection signal) from the text identification block will match the R'/G'/B' image signal. In other words, the line image at this point in time would be as follows: R'/G'/B' image signal = MJ signal (text detection signal) Figure 101. Text identification EN Copy module 211