HP 8550 Service Manual - Page 216

R/G/B->L/Ca/Cb conversion, L/CaCb->R/G/B conversion As shown in figure 97 on page 207, in the R/G/B->L/Ca/Cb conversion block, the RGB image signal is converted to chromatic spaces of L (light area component) and Ca/Cb (color component). L=(R+2G+B)/4 Ca=(R-G)/2 Cb=(R+G-2B)/4 Using L/Ca/Cb, the copy module performs spatial filter processing and chromatic identification. After spatial filter processing and chromatic identification, the copy module then performs L/Ca/Cb->R/ G/B conversion. R=(4L+5Ca+2Cb)/4 G=(4L-3Ca+2Cb) B=(4L+Ca-6Cb)/4 Spatial filter processing / chromatic identification The copy module performs spatial filter processing based on the edge component computed from the L (luminous component) signal and the Ca/Cb (chromatic component) signal component and the MJ (text detection) signal from the text identification block. During spatial filter processing, the copy module performs computations to generate images which are sharp or soft according to the combination of printing modes selected on the control panel, or the sharpness setting on the control panel. If image data as shown in figure 104 on page 215 is input and "lower sharpness" is selected, the output level will be as shown in figure 105 on page 215. With the "lower sharpness" setting, the variations in density of an image are evened out to produce a soft image. In "higher sharpness," the contrast of an image is emphasized to produce a crisp image. 214 Chapter 5 - Theory of operation EN