Scanning Projection Apparatus Tangential Distortion Compensation
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Solution Overview
Problem
Scanning projection systems suffer from spatial distortions such as sinusoidal and tangential distortion, particularly at larger scan angles, which affect image quality by stretching images around the edges.
Innovation Solution
The implementation of a scanning projection apparatus that uses a microelectromechanical system (MEMS) scanner with a scanning mirror control circuit to generate drive signals for the scanning mirror, compensating for tangential distortion by modifying the mirror movement and image processing to adjust pixel locations, using equations to ensure linear scan rates and interpolation for accurate pixel placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a scanning mirror is used to project images on a flat display surface, then the projection system can achieve wide scan angles and large display area, but tangential distortion occurs causing image stretching at the edges
Solution Approach 1:
The system pre-calculates and stores the nonlinear mapping relationship between distorted and undistorted pixel coordinates before image projection. This lookup table is created in advance based on the scan geometry, allowing real-time distortion compensation without complex calculations during actual projection, thus maintaining both large display area and high geometric accuracy
Solution Approach 2:
The patent transforms the image coordinates using a nonlinear mapping function that changes the spatial parameters of pixel locations. By applying this coordinate transformation based on the scan angle and position, the system compensates for tangential distortion and restores geometric accuracy across the entire display area including edges
2Area of stationary object
If the scan angle is increased to improve display coverage, then the projection can cover larger areas, but tangential distortion becomes more significant causing greater image stretching
Solution Approach 1:
The system pre-calculates position correction values for all possible scan angles and positions, storing them in a lookup table. This allows the system to handle large scan angles with high position accuracy by simply retrieving pre-computed correction values, avoiding the need for complex real-time calculations while maintaining precision across the entire scan coverage area
3Device complexity
If a simple linear scan is used, then the control system is simple, but sinusoidal distortion and tangential distortion occur simultaneously degrading image quality
Solution Approach 1:
The system uses pre-computed lookup tables that contain all necessary distortion compensation data for both sinusoidal and tangential distortion. This approach maintains simple control hardware while achieving high geometric accuracy by replacing complex real-time control algorithms with straightforward table lookups and coordinate transformations
Solution Approach 2:
The patent introduces an intermediary coordinate transformation step that maps distorted image coordinates to undistorted coordinates using a lookup table. This intermediary process separates the simple scanning control from the complex distortion compensation, allowing each to be optimized independently while achieving both simplicity and high image quality
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 reduces horizontal and vertical position errors, eliminating tangential distortion and maintaining image quality across the entire scan trajectory, even at large scan angles.
Implementation Method 1
A scanning projection apparatus sweeps a light beam in a fast-scan sinusoidal dimension and a slow-scan dimension
Data Source
AI summary
A scanning projector includes a scanning mirror that sweep a beam in two dimensions. Tangential distortion in a fast-scan dimension is compensated by incorporating a tangent function when determining the light beam location and interpolating pixel data. Tangential distortion in a slow-scan dimension is compensated by driving the scanning mirror nonlinearly in the slow scan dimension such that the light beam sweeps across the display surface at a constant rate.