Focus Detecting Pixels Readout Mode Control for Low Light Autofocus
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Solution Overview
Problem
Image plane phase difference autofocus mechanisms in digital photographing devices face challenges in focus detection under low brightness conditions due to insufficient charge accumulation time for focus detecting pixels, which also complicates circuit configuration and increases noise, and reduces the ability to display live-view images at a high frame rate.
Innovation Solution
An apparatus and method that dynamically adjust the readout mode of focus detecting pixels based on object brightness, allowing for extended exposure time in low light conditions to improve focus detection efficiency while maintaining live-view display frame rates, and switching to a high frame rate mode when brightness is normal to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge accumulation time of focus detecting pixels is increased to improve focus detection under low brightness conditions, then focus detection capability is improved, but the overall frame processing time increases and live-view frame rate decreases
Solution Approach 1:
The patent divides the image sensor pixels into two distinct groups: focus detecting pixels and live-view pixels. This segmentation allows independent control of charge accumulation times for each group, enabling focus detecting pixels to have extended exposure time for low-light focus detection while live-view pixels maintain their original frame rate timing, thus resolving the contradiction between focus detection capability and live-view frame rate
Solution Approach 2:
The patent implements dynamic adjustment of readout modes based on brightness conditions. The control unit dynamically selects between first readout mode (extended exposure for focus pixels only) and second readout mode (normal exposure for all pixels) according to detected brightness levels, allowing the system to adaptively optimize focus detection capability while maintaining live-view frame rate under different lighting conditions
2Adaptability or versatility
If separate signal lines are provided for each pixel to enable independent charge accumulation time adjustment, then charge accumulation time control flexibility is improved, but circuit complexity and noise increase
Solution Approach 1:
The patent segments the pixel array into focus detecting pixels and live-view pixels with distinct readout paths. By providing separate signal lines only for focus detecting pixels rather than every pixel, the system achieves the necessary control flexibility for independent charge accumulation time adjustment while minimizing circuit complexity and noise
Solution Approach 2:
The patent makes focus detecting pixels multi-functional by enabling them to serve both as focus detection elements (with extended exposure time) and as part of the overall image sensor array. This universal design allows the same pixel structure to perform multiple functions without requiring completely separate circuits for each pixel
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
Enhances focus detection efficiency under low brightness conditions while maintaining live-view display frame rates and reducing power consumption by adjusting the readout mode of focus detecting pixels based on object brightness, ensuring effective focus detection and efficient power usage.
Implementation Method 1
an image sensor that includes focus detecting pixels
Implementation Method 2
the charge accumulation time (or exposure time) of the focus detecting pixels may be insufficient
Data Source
AI summary
An image sensor control device includes an image sensor including focus detecting pixels; an object brightness detecting unit that detects brightness of an object; a mode determining unit that determines a first readout mode or a second readout mode based on the detected brightness of the object; a read-out unit that reads out the focus detecting pixels in the determined readout mode; and a focus detecting unit that performs focus detection by using focus detection data read out from the focus detecting pixels. In an implementation, in the first readout mode, the read-out unit reads out the focus detecting pixels in a first interval, and, in the second readout mode, the read-out unit reads out the focus detecting pixels in a second interval, which is longer than the first interval.