Screen Generation Using PWM Reference Vectors for Halftone Control
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Solution Overview
Problem
Electrophotographic systems face challenges in producing high-quality multi-gradation images due to low resolution, leading to geometrical errors and unsightly textures, particularly at 600 dpi, where increasing halftone dot size reduces resolution and results in granularity and color moire issues.
Innovation Solution
A method using Pulse Width Modulation (PWM) technique with reference position data to increase image resolution from 600 dpi to 1800 dpi by employing two reference vectors for generating screens, allowing for more flexible halftone dot formation and reduced granularity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the basic size of halftone dot is increased to increase pseudo gradation levels, then gradation reproduction is improved, but resolution decreases
Solution Approach 1:
The patent transitions from spatial dimension only to temporal-spatial dimension by introducing time-based PWM control. Instead of relying solely on larger halftone dots for gradation, the invention uses pulse width modulation where the duration of toner application varies to create gradation effects, effectively adding a temporal dimension to the halftoning process and maintaining fine spatial resolution.
Solution Approach 2:
The invention changes the control parameter from static halftone dot size to dynamic pulse width and reference position. By varying the pulse width (duration) and reference position (starting point) of toner application pulses, the system achieves multi-gradation levels without increasing the physical size of halftone dots, thus maintaining high resolution while improving gradation reproduction.
2Manufacturing precision
If halftoning is executed using created threshold matrix, then gradation is reproduced, but geometrical errors of halftone centers occur causing unsightly textures
Solution Approach 1:
The patent implements feedback control by continuously monitoring and adjusting the reference position based on accumulated phase shifts. The system calculates the phase shift caused by digital restrictions and uses this feedback to correct the reference position in subsequent cycles, preventing the accumulation of geometrical errors and maintaining accurate halftone center positions.
Solution Approach 2:
The invention performs preliminary calculation of phase shifts and reference position adjustments before actual halftoning. By pre-computing the necessary corrections based on the threshold matrix and resolution conversion requirements, the system eliminates geometrical errors before they manifest as visual defects in the output image.
3Manufacturing precision
If screen of about 200 lines is used in 600 dpi electrophotography, then gradation can be reproduced, but degree of freedom in screen specification is low and color moire occurs
Solution Approach 1:
The patent transforms static screen specification into a dynamic control system. Instead of being constrained to fixed screen line numbers and angles, the invention dynamically adjusts the reference position and pulse width for each pixel based on the desired screen parameters. This allows the system to adaptively specify screens with various line numbers and angles, including irrational values, without being limited by the underlying 600 dpi hardware resolution.
Data Source
AI summary
Disclosed is a method of generating a screen for an image processing apparatus, which reproduces a multi-gradation image in one pixel using a PWM technique for controlling a pulse width and reference position data. The method includes inputting image data with a first resolution, virtually increasing the first resolution to a second resolution using the reference position data, and generating a screen with the second resolution with respect to the image data using two reference vectors based on the reference position data.