Signal Normalization for Accurate Focus Detection
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Solution Overview
Problem
Conventional image capturing apparatuses face challenges in focus detection accuracy due to insufficient signal amplitudes resulting from band-pass filtering, leading to potential reductions in focus detection precision, especially when dealing with objects of low contrast or high frequency components.
Innovation Solution
The implementation of a normalization processing system using normalization coefficients to adjust signal amplitudes, combined with correlation calculation and correction mechanisms to ensure accurate focus detection, independent of signal frequency components, through the use of band-pass filters and peak value detection to determine appropriate normalization gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If normalization processing is performed with the sum of absolute values of filter coefficients to suppress signal amplitude, then bit width is reduced, but focus detection accuracy deteriorates when applied to objects with low contrast or high frequency components
Solution Approach 1:
The patent applies dynamic normalization by calculating normalization coefficients based on the actual frequency characteristics of the input signal. Instead of using fixed normalization values, the system adaptively adjusts normalization coefficients according to the detected frequency band, thereby maintaining appropriate signal amplitudes for both low-contrast and high-frequency objects while preserving focus detection accuracy.
Solution Approach 2:
The patent changes the normalization parameter from a fixed value (sum of absolute filter coefficients) to a dynamic value derived from frequency characteristic detection. By detecting the frequency band of the input signal and selecting appropriate normalization coefficients accordingly, the system optimizes signal amplitude for different object types without sacrificing measurement precision.
2Quantity of substance
If no normalization processing is performed, then signal amplitude is preserved, but bit width increases requiring larger circuit size
Solution Approach 1:
The patent implements dynamic bit width management by calculating normalization coefficients that adapt to the input signal's frequency characteristics. This dynamic approach ensures that bit width is minimized only when necessary (for high-frequency signals) while preserving full precision for low-frequency signals, thereby reducing overall circuit size without permanently sacrificing signal amplitude quality.
Solution Approach 2:
The patent changes the bit width parameter dynamically based on frequency detection results. Instead of using a fixed large bit width for all cases, the system adjusts the effective bit width according to the signal's frequency content, reducing circuit size for high-frequency signals while maintaining full precision for low-frequency signals where amplitude preservation is critical.
3Measurement precision
If band-pass filter is applied to extract specific frequency band, then focus detection is enhanced, but signal amplitude becomes insufficient for accurate focus detection
Solution Approach 1:
The patent implements a feedback mechanism where the frequency characteristics of the band-pass filtered signal are detected, and this information is used to determine appropriate normalization coefficients. The detected frequency band feeds back into the normalization process, ensuring that the filtered signal receives appropriate amplitude adjustment based on its specific frequency content, thereby restoring sufficient signal amplitude for accurate focus detection.
Solution Approach 2:
The patent introduces normalization coefficients as an intermediary element between the band-pass filter and the focus detection calculation. These coefficients act as a mediator that adjusts the amplitude of the filtered signal based on its frequency characteristics, bridging the gap between frequency-selective filtering and amplitude-sufficient focus detection without requiring changes to the filter itself.
Data Source
AI summary
A control apparatus (105) includes a normalizer (400, 401) that performs normalization processing on a first signal and a second signal by using normalization coefficients related to the first signal and the second signal, respectively, a correlation calculator (402) that performs correlation calculation with respect to the normalized first and second signals, and a corrector (403, 800, 801) that corrects correlation data to cancel the normalization processing, and the correlation data is based on an output signal from the correlation calculator.