Optical Low Pass Filter Diagonal Moire Reduction
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Solution Overview
Problem
Existing optical low pass filters struggle to reduce moire and false color in the diagonal direction while maintaining perceived resolution in the vertical/horizontal direction, as they either fail to adequately address diagonal moire or excessively reduce horizontal resolution.
Innovation Solution
An optical low pass filter design using four birefringent plates with specific optic axis orientations and separation widths, where the orthogonal projection of the optic axis of one plate forms angles of 45° and 90° relative to the image-capturing element's sides, and the separation widths satisfy the condition 1.15 < b/a < 3, to selectively reduce cut-off frequency in the diagonal direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the optical low pass filter is designed to reduce moire in the vertical/horizontal direction, then moire in the vertical/horizontal direction is reduced, but false color due to moire in the diagonal direction is generated
Solution Approach 1:
The patent applies different separation widths to different orientations of birefringent plates. Specifically, plates oriented at 45° to the image-capturing element sides have a different separation width compared to plates oriented parallel to the sides. This local differentiation allows the filter to independently control moire reduction in vertical/horizontal directions versus diagonal directions, resolving the contradiction between reducing vertical/horizontal moire and preventing diagonal false color.
2Object-affected harmful factors
If the optical low pass filter is designed to reduce moire in the diagonal direction, then moire in the diagonal direction is reduced, but perceived resolution in the vertical/horizontal direction is excessively reduced
Solution Approach 1:
The patent employs different separation widths for different plate orientations: a first separation width for plates oriented at 45° to the image-capturing element sides, and a second separation width for plates oriented parallel to the sides. By locally optimizing the separation width for each orientation, the filter effectively reduces diagonal moire while preserving vertical/horizontal resolution, as each direction receives the appropriate level of filtering strength.
3Device complexity
If the separation width of all birefringent plates is set equally, then the structure is simple, but frequency characteristics are not uniform across different directions
Solution Approach 1:
The patent specifies different separation widths for different plate orientations: plates at 45° to the image-capturing element sides have one separation width, while plates parallel to the sides have another separation width. This differentiation ensures uniform frequency characteristics across all directions by locally adjusting the separation width to compensate for the directional sensitivity of the image-capturing element, achieving isotropic frequency response despite the increased structural complexity.
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 design effectively reduces moire and false color in the diagonal direction while preserving perceived resolution in the vertical/horizontal direction by adjusting the cut-off frequency ratio between diagonal and vertical/horizontal directions.
Implementation Method 1
a first birefringent plate of which an orthogonal projection of an optic axis onto the light-receiving surface is parallel to a long side of the image-capturing element; a second birefringent plate of which an orthogonal projection of an optic axis onto the light-receiving surface is parallel to a short side of the image-capturing element
Data Source
AI summary
An optical low pass filter includes a first birefringent plate, a second birefringent plate, a third birefringent plate, and a fourth birefringent plate. A conditional expression of 1.15<b/a<3 is satisfied, in a case where a separation width of an incident light ray in each of the first birefringent plate and the second birefringent plate is set to be a and a separation width of an incident light ray in each of the third birefringent plate and the fourth birefringent plate is set to be b.