Lens Roll-Off Correction via Inverse Transfer Function
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Solution Overview
Problem
Wireless phone cameras face challenges with lens roll-off degradation, causing brightness and color tone shifts due to small lens sizes and misalignment, which affect image quality and consumer perception.
Innovation Solution
Applying an inverse transfer function to captured images by measuring the lens transfer function through a flat field image, generating a correction curve that can be stored as a polynomial or piecewise continuous function, and applying it to subsequent images to compensate for lens degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a smaller lens size is used to reduce device cost and size, then device cost and dimensions are reduced, but lens roll-off degradation occurs causing brightness and color tone shifts
Solution Approach 1:
The patent applies preliminary action by measuring the lens transfer function using a flat field image before actual image capture, and pre-calculating the inverse transfer function and correction curves. This allows the correction data to be stored and applied during normal operation, compensating for the inherent roll-off degradation of small lenses without requiring larger, more expensive optics.
2Manufacturing precision
If lens roll-off correction is applied through software processing, then image quality is improved, but processing complexity increases
Solution Approach 1:
The correction curves and inverse transfer functions are pre-calculated and stored in lookup tables during manufacturing or initial setup. During actual image capture and processing, the system simply applies these pre-computed corrections rather than performing complex real-time calculations, significantly reducing processing complexity while maintaining image quality improvement.
Data Source
AI summary
Brightness and color tone shift distortion of captured images by a non-ideal lens can be compensated by applying an inverse transfer function to the captured image. An estimate of the lens transfer function can be measured based on a radius from a center of the lens. The lens transfer function can be measured by capturing a flat field image. The center of the lens can be determined based on a relative brightness maximum. The relative brightness of the captured flat field image can then be measured as a function of radius to generate a lens response curve. Separate response curves can be measured for each color component. A correction curve can be determined as the inverse of the response curve. The correction curve can be applied to subsequent captured images to compensate for lens degradation.