CHAPTER 4 IMAGE PROCESSING SYSTEMCOPYRIGHT © 1999 CANON INC. CANON CLC1120/1130/1150 REV.0 MAR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON) 4-11I. Logarithmic Correction and BGR-to-YMC Conversiona. Logarithmic CorrectionThe output of the CCD possesses linear characteristics in relation to the intensity of lightreflected by an original. The density as perceived by the eye, however, does not necessarily havelinear characteristics.To compensate for the discrepancy, the copier performs level conversion as shown in Figure 4-408.b. BGR-to-YMC ConversionThe intensity of light passing through each of the filters (B, G, R) of the CCD and the densityof (Y, M, C) of an original are in a complementary relationship, enabling level conversion (B to Y,G to M, R to C) as shown in Figure 4-409 and generation of Y, M, and C signals.Figure 4-408 Logarithmic Correction Figure 4-409 BGR-to-YMC Conversion0 255255Output levelInput level0 255255Output level(Y, M, C)DarkerLighterInput level (B, G, R)
