Camera Focus Detection Using Adaptive Charge Accumulation
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Solution Overview
Problem
Existing camera systems using storage-type sensors for focus detection face issues with signal flattening when the luminance of the main photographic subject is low, leading to inaccurate focus detection.
Innovation Solution
A camera system comprising a first storage-type sensor, a focus detection unit, a second image-acquiring sensor, and a control unit that extracts the main photographic subject region and adjusts the accumulation of electrical charge to achieve appropriate sensitivity for focus detection, using a phase detection method and separating the main subject from background regions based on hue and luminance differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the accumulation time period is determined based on the high luminance portion of the photographic field, then the saturation level is controlled for bright areas, but the detection signal from low luminance subjects becomes flattened and inaccurate
Solution Approach 1:
The patent applies local quality by determining accumulation time period separately for different luminance regions. The control unit divides the photographic field into high luminance portions and other portions, then sets different accumulation time periods for each region based on their respective luminance characteristics, ensuring optimal signal quality for both bright and dark areas
Solution Approach 2:
The patent implements dynamics by making the accumulation time period adjustable and adaptive. The control unit dynamically determines the accumulation time period based on detected luminance values, switching between different time periods for different regions and updating these settings based on current imaging conditions rather than using fixed parameters
2Device complexity
If a single accumulation time period is used for the entire sensor, then the device complexity is reduced, but the focus detection accuracy for subjects with varying luminance deteriorates
Solution Approach 1:
The patent applies parameter changes by varying the accumulation time period parameter based on luminance conditions. The control unit changes the accumulation time period from a first value for high luminance regions to a second value for other regions, optimizing the detection signal for each luminance category without requiring completely different sensor configurations
3Measurement precision
If the accumulation time period is extended to capture low luminance subjects, then the signal from dark areas improves, but the high luminance portions become overexposed and saturated
Solution Approach 1:
The patent applies segmentation by dividing the sensor or photographic field into multiple regions based on luminance characteristics. The control unit identifies high luminance portions separately from other portions and applies different accumulation time periods to each segment, preventing signal saturation in bright areas while maintaining adequate sensitivity in darker regions
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 allows for accurate focus detection by ensuring the sensitivity of the range-finding sensor matches the luminance of the main subject, reducing background influence and improving calculation efficiency, resulting in precise defocus amount calculation and compact camera design.
Implementation Method 1
a first sensor of a storage type that has a plurality of pixels... controls accumulation of electrical charge by the first sensor
Implementation Method 2
a focus detection unit that detects a focus adjustment state of a photographic optical system... performs focus detection calculation by a phase detection method in which a defocus amount is calculated according to a gap between a pair of images
Data Source
AI summary
A camera includes: a first sensor of a storage type that has a plurality of pixels; a focus detection unit that detects a focus adjustment state of a photographic optical system based upon a detection signal from the first sensor for a photographic subject; a second sensor that acquires an image of the photographic subject; an extraction unit that extracts a main photographic subject region from image information acquired by the second sensor; and a control unit that controls accumulation of electrical charge by the first sensor, based upon values outputted from pixels of the first sensor that correspond to the main photographic subject region.