Multi Color Autofocus Using Sequential Illumination
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Solution Overview
Problem
Existing autofocus systems face inaccuracies due to inherent camera noise and surface reflectivity variations, particularly when using small tile sizes for image acquisition, leading to unreliable data in determining focus height and surface topology.
Innovation Solution
A sequential multicolored illuminator system with a camera and data processor that uses selectively activated monochromatic light sources to acquire contrast information at multiple Z-axis positions, comparing signals from different wavelengths to determine a focus parameter, which improves accuracy by combining wavelength-dependent and position-dependent data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If small tile sizes are used for image acquisition, then dense Z-height data can be obtained from the surface, but the data becomes unreliable due to camera noise and surface reflectivity variation
Solution Approach 1:
The patent changes the illumination parameter by using multiple wavelengths (colors) of light. By illuminating the surface with different wavelengths and analyzing how contrast varies with wavelength, the system can distinguish between actual surface topology variations and artifacts caused by camera noise or surface reflectivity variations. This parameter change enables reliable measurements even with small tile sizes.
Solution Approach 2:
The patent introduces wavelength-dependent contrast information as an intermediary parameter. Instead of directly measuring Z-height from single-wavelength images, the system uses multi-wavelength contrast data as an intermediate step to calculate the focus height. This intermediary measurement helps filter out noise and reflectivity variations, improving data reliability.
2Measurement precision
If multiple wavelengths are used to improve focus accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent uses periodic action by sequentially activating different wavelength LEDs in a repeating cycle. The illuminator switches between red, green, and blue LEDs periodically, capturing images at each wavelength. This periodic illumination pattern simplifies the control logic compared to simultaneous multi-wavelength illumination, as the system only needs to cycle through available wavelengths rather than manage complex multi-channel illumination.
Solution Approach 2:
The patent discards images captured at non-optimal focus positions and recovers useful information only from images captured at or near the peak contrast position. By focusing analysis only on the most informative data points (those at peak contrast), the system reduces computational complexity while maintaining measurement precision.
3Measurement precision
If sequential multi-color illumination is used, then autofocus accuracy improves, but acquisition time increases
Solution Approach 1:
The patent applies partial action by not requiring complete focus sweeps at all wavelengths. Instead of performing exhaustive measurements, the system captures images at a limited number of Z-axis positions and uses the multi-wavelength contrast information to interpolate or calculate the optimal focus position. This partial measurement approach reduces acquisition time while maintaining accuracy.
Solution Approach 2:
The patent substitutes mechanical focus adjustment with optical wavelength variation. Instead of mechanically moving the camera or objective lens through the entire focus range and capturing images at each position, the system uses the optical property that different wavelengths focus at different positions. By varying wavelength rather than position, the system reduces mechanical movement and acquisition time.
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 approach enhances autofocus accuracy by calculating a more precise focus position through the combination of contrast information from multiple colors, reducing the impact of camera noise and surface reflectivity variations, and allows for reliable determination of surface topology and shape.
Implementation Method 1
a controllable light source having at least two selectively activated substantially monochromatic output wavelengths
Implementation Method 2
a camera receiving light from said light source reflected from a portion of said object and generating output signals responsive to said received light
Data Source
AI summary
An autofocus system and method that includes a controllable light source having at least two selectively activated substantially monochromatic output wavelengths adapted for illuminating an object; a camera receiving light from said light source reflected from a portion of said object and generating output signals responsive to said received light; a controller connected to said camera and said controllable light source for positioning said camera and sequentially illuminating a first portion of the object with at least two selectively activated substantially monochromatic output wavelengths, moving the camera to a second position and sequentially illuminating a second portion of the object with at least two selectively activated substantially monochromatic output wavelengths; and a data processor connected to said camera and receiving said output signals and for each portion, comparing the output signals associated with each wavelength and determining a focus parameter from said comparison.