HP 8550 Service Manual - Page 218
Logarithmic correction and BGR->YMC conversion, Logarithmic Correction
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Logarithmic correction and BGR->YMC conversion A Logarithmic Correction The output of the CCD has linear characteristics in relation to the light reflected by an original. However, the density perceived when looking at an original does not necessarily have linear characteristics. Figure 106 shows the relationship between the density of an original perceived by the eye and the output of the CCD. Figure 106. Original density compared to CCD output To correct the discrepancy, the copy module performs a level conversion as shown in figure 107. Figure 107. Density level conversion 216 Chapter 5 - Theory of operation EN
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216
Chapter 5 - Theory of operation
EN
Logarithmic correction and BGR->YMC conversion
A
Logarithmic Correction
The output of the CCD has linear characteristics in relation to the light
reflected by an original. However, the density perceived when looking
at an original does not necessarily have linear characteristics. Figure
106 shows the relationship between the density of an original
perceived by the eye and the output of the CCD.
Figure 106.
Original density compared to CCD output
To correct the discrepancy, the copy module performs a level
conversion as shown in figure 107.
Figure 107.
Density level conversion