Image Sensor Charge Accumulation Control for Phase Detection
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Solution Overview
Problem
Existing image capturing apparatuses face challenges in achieving high-speed focus detection using the phase difference technique during moving picture display, as previous solutions either compromise frame rate or suffer from reduced sensitivity due to increased signal wiring and noise amplification.
Innovation Solution
An image capturing apparatus with a two-dimensional image sensor featuring image sensing pixels and discretely arranged focus detection pixels that divide the pupil region, allowing for switching between all-pixel and thinning readout modes, and independent charge accumulation control for imaging and focus detection rows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus detection pixels are arranged in rows that are read out during thinning readout mode, then phase difference focus detection can be performed, but the frame rate of moving images decreases due to the need to read out additional rows
Solution Approach 1:
The patent implements dynamic control of charge accumulation timing for focus detection pixels, allowing the system to adaptively adjust accumulation periods based on whether still image or moving image capture is performed. During moving image capture, the accumulation period is shortened to match the reduced readout frequency of focus detection rows, thereby maintaining acceptable focus detection performance while preserving high frame rates.
2Productivity
If focus detection pixels are arranged in rows not read out during thinning readout mode, then frame rate is maintained, but the signal-to-noise ratio deteriorates due to insufficient charge accumulation time
Solution Approach 1:
The patent changes the accumulation time parameter dynamically based on the readout mode and capture type. During still image capture, full accumulation time is used for maximum signal-to-noise ratio. During moving image capture, the accumulation time is reduced proportionally to the reduced readout frequency, balancing signal quality with frame rate requirements.
3Measurement precision
If independent accumulation control is implemented for imaging rows and focus detection rows, then charge accumulation can be optimized for each function, but the device complexity increases due to additional control circuits
Solution Approach 1:
The patent segments the image sensor into distinct imaging regions and focus detection regions, with independent control signals for each segment. This allows separate optimization of accumulation timing for each function while using a modular control architecture that manages complexity through regional division rather than universal control.
4Measurement precision
If all pixels are read out during moving picture display, then image quality is maintained, but the processing load increases and frame rate decreases
Solution Approach 1:
The patent applies partial readout by selectively reading out only imaging rows during moving picture display, while focus detection rows are read out at reduced frequency. This partial action approach maintains sufficient image quality for display purposes while reducing the overall processing load to achieve higher frame rates.
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
Improves the signal-to-noise ratio of focus detection pixels during phase difference focus detection, enabling high-speed focus adjustment without increasing signal wiring complexity or noise amplification, thus enhancing focus detection performance.
Implementation Method 1
image sensing pixels that generate a signal for image generation by photoelectrically converting an object image formed by an imaging lens, and focus detection pixels that divide the pupil region of the imaging lens into pupil regions and generate a signal for phase difference detection by photoelectrically converting object images from the pupil regions
Data Source
AI summary
An image capturing apparatus includes: an image sensor including image sensing pixels that generate a signal for image generation, and focus detection pixels dividing the pupil region of an imaging lens into pupil regions and generating a signal for phase difference detection by photoelectrically converting object images from the pupil regions obtained by the division; a switching unit that switches between an all-pixel readout mode in which signals from all of the multiple pixels are read out and a thinning readout mode in which the signals of the multiple pixels are thinned and read out; and a control unit that, in the case where the mode has been switched by the switching unit to the thinning readout mode, controls the accumulation of charges in imaging rows used for image generation and focus detection rows including the focus detection pixels independent from each other.