Multi-Frequency AF Circuit for Transparent Cell Focus
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Solution Overview
Problem
Conventional auto focus methods, such as contrast AF, struggle with precise focus adjustment for transparent objects like non-colored cells due to double peaks in contrast values, which are affected by cell type, illumination angle, and vessel conditions, leading to inconsistent focus precision.
Innovation Solution
An observation device and focus adjustment method that calculate focus evaluation values across multiple frequency bands to determine the focus position based on maximum or minimum values, selecting the appropriate peak or minimum value to achieve precise focus regardless of cell type and environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If conventional contrast AF method is used for transparent objects like non-colored cells, then focus adjustment can be performed automatically, but focus precision deteriorates due to double peak phenomenon in contrast values
Solution Approach 1:
The patent segments the contrast evaluation into multiple frequency bands (low frequency band and high frequency band) by applying different filter conditions to the image data. This allows separate evaluation of contrast characteristics at different spatial frequencies, enabling reliable focus detection even when double peaks occur in the overall contrast curve.
Solution Approach 2:
The patent changes the evaluation parameter from a single contrast value to multiple frequency-band-specific contrast values. By calculating contrast values for different frequency bands and comparing their relationships, the system can distinguish between double peak phenomena and actual focus positions, thereby maintaining high focus precision.
2Device complexity
If single frequency band contrast calculation is used, then calculation is simple, but focus detection reliability deteriorates due to double peak or single peak variations depending on cell type and environment
Solution Approach 1:
The patent divides the frequency spectrum into multiple bands and evaluates contrast separately in each band. This segmentation allows the system to identify consistent focus indicators across different frequency ranges, improving reliability without requiring overly complex multi-dimensional analysis.
Solution Approach 2:
The patent applies partial action by selectively evaluating contrast in specific frequency bands based on the detection scenario. The system can adaptively choose which frequency bands to analyze, performing sufficient evaluation to ensure reliable focus detection while avoiding unnecessary computational complexity.
3Measurement precision
If focus evaluation is based on contrast minimum between double peaks, then focus position can be detected for some cell types, but detection accuracy deteriorates when single peak occurs or peaks are close together
Solution Approach 1:
The patent changes the evaluation approach from relying on contrast minimum detection to analyzing the relationship between contrast values at different frequency bands. By comparing low frequency band contrast with high frequency band contrast, the system can reliably identify focus positions regardless of whether double peaks or single peaks occur in the overall contrast curve.
Data Source
AI summary
An observation device, comprising an image sensor that forms images of a specimen and outputs an image signal, an AF detection circuit that calculates evaluation values based on the image signal, and a focus control circuit that controls focus position based on the evaluation values, wherein the AF detection circuit calculates a plurality of evaluation values based on signals relating to a plurality of frequency bands of the image signal, and the focus control circuit controls focus position based on maximum value or minimum value of the plurality of evaluation values.