Canon iR C6800 Series Service Manual page 201

<Particulars of Control>
White Plate Dust Detection
The machine compares the shading coefficient obtained from shift shading and the shading coefficient obtained from
fixed shading to identify the presence/absence of dust and, if any, coordinates and width of the area.
White Plate Dust Correction
If the machine detects dust as a result of white plate dust detection, it corrects the shading coefficient of the area
using the shading coefficient of both sides so as to decrease the effects of the presence of dust. It executes shading
correction using the coefficient it obtains after correction.
If the result of white plate dust detection indicates the presence of dust, the shading coefficient of the area in question
will be corrected by the coefficients of its adjacent areas during shading correction with the aim of reducing the
effects of the presence of dust. Thereafter, shading correction will be executed using the corrected coefficient.
White plate
Reference area
(Shading coefficient
computation area)
Computation of shading
coefficient
Area
(shift shading to
of dust
reference area)
Fixing shading position
Shading correction position
F-5-30
Detection Algorithm
Computation of shading
coefficient
(from fixed shading to
shading correction position)
Comparison
Detection of coordinates of
start of dust and width
Correction Algorithm
Correction of dust area
coefficient using data of both sides
Chapter 5
5-19