Multi-Wavelength Lighting for Monochromatic Camera Contrast
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Solution Overview
Problem
Monochromatic cameras struggle to capture images of planar and specular objects with adequate contrast, which is crucial for identifying minor features and defects in semiconductor wafers and chip carriers, as existing lighting systems restrict the field of view and do not effectively highlight subtle surface features.
Innovation Solution
The method employs multi-wavelength lighting to capture a plurality of images and optimizes contrast between surface portions using a contrast optimization algorithm, which determines the most suitable wavelength for maximum contrast and applies active noise cancellation to create a synthetic image with enhanced contrast between targets and backgrounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If monochromatic cameras with single-wavelength lighting are used, then the system is simple and fast, but image contrast of planar specular objects is inadequate
Solution Approach 1:
The lighting system is segmented into multiple independent wavelength sources (e.g., blue LED at 470nm, green LED at 530nm, red LED at 630nm). Each wavelength can be independently controlled and optimized for specific surface features, allowing the system to achieve high contrast images by selecting appropriate wavelengths without requiring complex integrated lighting solutions.
Solution Approach 2:
The patent changes the wavelength parameter of the light source to optimize image contrast. By varying the wavelength across multiple discrete values (blue, green, red channels), the system can exploit different reflectance characteristics of planar specular objects at different wavelengths, thereby achieving adequate contrast without increasing overall system complexity.
2Illumination intensity
If multi-wavelength lighting is used to improve contrast, then image quality improves, but the number of images captured increases
Solution Approach 1:
The patent merges multiple single-wavelength images into a composite color image. By capturing images at different wavelengths (blue, green, red) and combining them, the system achieves enhanced contrast and color information in a single composite image, rather than requiring separate analysis of multiple images.
Solution Approach 2:
The lighting system uses periodic modulation of multiple wavelength sources in a structured sequence (e.g., illuminating with blue, then green, then red wavelengths in succession). This periodic action allows the system to capture multiple wavelength images efficiently and combine them, reducing total capture time compared to continuous multi-wavelength illumination.
3Measurement precision
If narrow-angle dark field lighting is used, then minor surface features are highlighted, but the field of view is restricted
Solution Approach 1:
The patent transitions from relying solely on spatial arrangement (narrow-angle lighting geometry) to utilizing the spectral dimension (wavelength variation). By introducing wavelength as an additional dimension for contrast enhancement, the system can use broader lighting angles to maintain a wide field of view while still achieving high contrast for minor surface features through wavelength-specific reflectance differences.
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 significantly improves image quality by maximizing contrast and signal-to-noise ratio, enabling more accurate identification of marks and features on specular surfaces, even when they are not perfectly uniform or textured, thereby enhancing the performance of target identification algorithms.
Implementation Method 1
a first light source comprising a blue light emitting diode having a peak output at a wavelength of about 470 nanometers, a second light source comprising a green light emitting diode having a peak output at a wavelength of about 530 nanometers, and a third light source comprising a red light emitting diode having a peak output at a wavelength of about 630 nanometers
Implementation Method 2
a monochromatic camera tuned to a wavelength between 400 and 500 nanometers
Data Source
AI summary
A method and apparatus to improve image quality in images captured via monochromatic cameras using multi-wavelength lighting. A contrast optimization algorithm determines which particular wavelength among those available is most suitable to maximize contrast. The quality of the image can be further improved through active noise cancellation by determining the lighting schemes that provide maximum and minimum contrast between a target and a background. The elimination of image texture data (i.e., noise) is then accomplished through pixel-by-pixel division of the maximum by the minimum contrast image. Alternatively, images obtained using at least two wavelengths can be algebraically combined for noise reduction. The resulting composite image can be fed into any known target identification algorithm.