Ricoh A229 Service Manual page 12

2.2.1 OVERVIEW.................................................................................... 2-16
2.2.2 SCANNER DRIVE.......................................................................... 2-17
2.2.3 ORIGINAL SIZE DETECTION IN BOOK MODE............................ 2-18
2.3 IMAGE PROCESSING............................................................................ 2-20
2.3.1 OVERVIEW.................................................................................... 2-20
2.3.2 SBU................................................................................................ 2-21
2.3.3 AUTO IMAGE DENSITY (ADS) ..................................................... 2-22
2.3.4 IPU (IMAGE PROCESSING UNIT) ................................................ 2-23
Overview ............................................................................................ 2-23
2.3.5 IMAGE PROCESSING STEPS AND RELATED SP MODES ........ 2-24
2.3.6 AUTO SHADING............................................................................ 2-30
Black level correction ......................................................................... 2-30
White level correction ......................................................................... 2-30
2.3.7 TEXT/PHOTO AREA SEPARATION ............................................. 2-31
Edge Determination ........................................................................... 2-31
Dot Screen Determination .................................................................. 2-32
Final Evaluation.................................................................................. 2-32
2.3.8 BACKGROUND ERASE ................................................................ 2-33
2.3.9 INDEPENDENT DOT ERASE........................................................ 2-34
2.3.10 FILTERING, MAIN SCAN MAGNIFICATION/REDUCTION......... 2-36
Overview ............................................................................................ 2-36
Filtering .............................................................................................. 2-36
Main scan magnification/reduction ..................................................... 2-37
2.3.11 GAMMA (γ) CORRECTION.......................................................... 2-38
2.3.12 GRADATION PROCESSING ....................................................... 2-38
Error Diffusion and Dithering .............................................................. 2-39
Grayscale Processing ........................................................................ 2-39
2.3.13 LINE WIDTH CORRECTION ....................................................... 2-40
2.3.14 COMPRESSION AND STORAGE ............................................... 2-41
Circuit ................................................................................................. 2-41
Compression ...................................................................................... 2-42
Image Rotation................................................................................... 2-42
2.4 LASER EXPOSURE ............................................................................... 2-43
2.4.1 OVERVIEW.................................................................................... 2-43
2.4.2 OPTICAL PATH ............................................................................. 2-44
2.4.3 AUTO POWER CONTROL ............................................................ 2-45
2.4.4 DUAL BEAM WRITING.................................................................. 2-46
2.4.5 LASER BEAM PITCH CHANGE MECHANISM ............................. 2-47
2.4.6 LD SAFETY SWITCHES................................................................ 2-48
2.5 DRUM UNIT............................................................................................ 2-49
2.5.1 PROCESS CONTROL ................................................................... 2-49
Overview ............................................................................................ 2-49
Drum potential sensor calibration....................................................... 2-50
VSG adjustment ................................................................................. 2-50
VG Adjustment ................................................................................... 2-51
LD power adjustment ......................................................................... 2-52
VREF Update ..................................................................................... 2-53
2.5.2 DRUM UNIT COMPONENTS ........................................................ 2-54
2.5.3 DRIVE MECHANISM ..................................................................... 2-55
A229 ii SM