Halftone Scanning Line Displacement for Moire Reduction
Solution Overview
Problem
Existing image forming apparatuses face challenges in reducing moire patterns due to periodic variations in scanning lines caused by manufacturing errors or misalignment of reflecting surfaces in rotating polygonal mirrors, which are not adequately addressed by current correction methods.
Innovation Solution
The apparatus includes a scanning unit that performs halftone processing and generates correction information to linearly displace the scanning start positions of successive scanning lines in the sub-scanning direction, aligning them along the direction of a vector forming a smaller angle with the sub-scanning direction to minimize moire patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If correction information is used to align scanning lines, then moire patterns are reduced, but measurement errors cause insufficient moire reduction
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction information in a lookup table that compensates for scanning line variations. This correction data is prepared in advance based on predetermined conditions (such as photoconductor rotation speed and scanning beam characteristics), allowing the system to proactively correct moire patterns before they manifest in the final image, rather than attempting to measure and correct them in real-time.
Solution Approach 2:
The patent changes parameters by systematically varying the correction information based on different operating conditions. The correction amount is adjusted according to photoconductor rotation speed, scanning beam characteristics, and halftone processing parameters. This parametric approach allows the system to adapt to different measurement scenarios and compensate for errors without requiring precise real-time measurement for each condition.
2Object-affected harmful factors
If scanning lines are aligned to reduce moire, then image quality improves, but device complexity increases due to correction mechanisms
Solution Approach 1:
The patent reduces device complexity by performing the complex correction calculations in advance and storing the results in a lookup table. The actual image formation process simply retrieves pre-computed correction values based on current operating parameters, avoiding the need for complex real-time calculation hardware or sophisticated measurement systems during operation.
Solution Approach 2:
The patent replaces what would otherwise require complex mechanical adjustment mechanisms with a computational approach. Instead of physically adjusting scanning line positions through mechanical means, the system uses digital correction of image data based on predetermined correction information, substituting mechanical complexity with algorithmic processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces moire patterns by ensuring precise alignment of scanning lines, even in the presence of measurement errors, thereby improving image quality and reducing the visibility of moire artifacts.
Implementation Method 1
a generating unit configured to perform halftone processing on image data to generate the image signal
Implementation Method 2
an electrophotographic image forming apparatus repeatedly scans a rotationally driven photoconductor with a scanning beam based on image data to form an electrostatic latent image on the photoconductor
Data Source
AI summary
An image forming apparatus includes: a scanning unit configured to form an electrostatic latent image on a photoconductor by scanning the photoconductor with one or more scanning beams in a main scanning direction based on an image signal, repetitively in a sub-scanning direction perpendicular to the main scanning direction; a generating unit configured to perform halftone processing on image data to generate the image signal; and a storage unit configured to store correction information. The correction information is set such that start positions of a plurality of scanning lines are linearly displaced to either a negative side or a positive side of the main scanning direction along the sub-scanning direction, in accordance with a direction of a first vector forming a smaller angle with the sub-scanning direction among two vectors in the halftone processing.