Image Forming Apparatus Pixel Size Correction for Moire Suppression
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Solution Overview
Problem
In electrophotographic image forming apparatuses without an fθ lens, magnification correction methods lead to moire interference due to varying pixel sizes in the main scanning direction, causing uneven image formation.
Innovation Solution
An image forming apparatus that includes a light source, a photosensitive member, a deflecting unit, a conversion unit, and a correction unit to specify and correct pixel sizes based on positions in the sub-scanning direction, replacing pixel arrangements in pixel groups to prevent moire interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If magnification correction is performed by varying pixel sizes in the main scanning direction, then image size uniformity is improved, but moire interference is generated
Solution Approach 1:
The image data is divided into multiple pixel groups along the sub-scanning direction, and pixel size variation is applied independently to each group. This segmentation approach allows magnification correction to be performed while disrupting the periodicity that causes moire interference, as different pixel groups have different correction patterns applied to them.
Solution Approach 2:
Different pixel size corrections are applied to different regions (pixel groups) along the sub-scanning direction. Each pixel group receives a locally optimized correction that accounts for the scanning speed variation at that position, while the variation between groups prevents moire formation.
2Manufacturing precision
If an fθ lens is used to achieve uniform scanning speed, then image quality is improved, but device complexity and cost increase
Solution Approach 1:
The optical fθ lens (mechanical/optical component) is replaced with an electronic correction system that processes image data. The correction unit varies pixel sizes in the main scanning direction based on position, achieving uniform image magnification through digital processing rather than optical means, thereby eliminating the need for complex and expensive fθ lenses.
3Manufacturing precision
If pixel clock frequency is modulated for magnification correction, then image size correction is achieved, but image distortion occurs
Solution Approach 1:
Instead of uniformly modulating the pixel clock frequency, the correction is segmented into discrete pixel groups along the sub-scanning direction. Each group undergoes independent correction with controlled pixel size variation, preventing the cumulative distortion that would result from continuous frequency modulation while achieving the desired magnification correction.
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
The solution effectively performs magnification correction while suppressing moire generation, ensuring consistent image quality by adjusting pixel sizes and arrangements to match the scanning direction.
Implementation Method 1
Laser light radiated to the photosensitive member is deflected in a longitudinal direction (hereinafter referred to as 'main scanning direction') of the photosensitive member with rotation of a rotary polygon mirror
Implementation Method 2
with the rotation of the photosensitive member, the scanning is performed also in a direction orthogonal to the main scanning direction (hereinafter referred to as 'sub-scanning direction')
Implementation Method 3
the laser light deflected with the rotation of the rotary polygon mirror is radiated to the photosensitive member via an fθ lens so that the laser light has a uniform optical path length and angle of incidence in the longitudinal direction of the photosensitive member
Data Source
AI summary
An image forming apparatus, including: a light source; a photosensitive member rotatable in a first direction; a deflecting unit configured to deflect the light beam in a second direction orthogonal to the first direction; a conversion unit configured to convert image data into a plurality of bit data corresponding to a density on a pixel-by-pixel basis; a specifying unit configured to specify a pixel size that is a number of divided pixels forming a pixel according to a position of the pixel in the second direction; and a correction unit configured to correct the plurality of bit data according to the pixel size, wherein the specifying unit specifies pixel sizes of pixels after an arrangement of the pixels in the second direction is replaced for each pixel group, the pixel group being obtained by dividing, with respect to each predetermined number of pixels, pixels arranged in the second direction.