Image Sensor Pixel Readout Control for Autofocus Speed
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Solution Overview
Problem
Conventional image capturing apparatuses using phase difference methods for focus detection face challenges in achieving high-speed focus detection during moving image display, as the readout of focus detection pixels is often thinned out, leading to reduced frame rates and accuracy.
Innovation Solution
The apparatus employs a control unit that switches between thinning and addition methods for imaging and focus detection lines, and performs secondary vertical scanning of focus detection pixels before or after primary scanning, allowing for efficient readout of focus detection signals in both high-resolution and high-speed modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thinning readout is performed on rows containing focus detection pixels to increase frame rate, then moving image display speed is improved, but focus detection accuracy deteriorates because focus detection pixel outputs are thinned out and may not be read out
Solution Approach 1:
The patent divides the readout process into two independent segments: one for imaging pixels and one for focus detection pixels. By separating the readout control for these two pixel types, the system can apply different thinning strategies to each, allowing focus detection pixels to be read out at full resolution while imaging pixels use thinning readout to maintain high frame rates.
Solution Approach 2:
The patent applies different readout qualities to different regions/pixel types. Focus detection pixels receive full readout (no thinning) to ensure high measurement precision, while imaging pixels receive thinned readout to optimize productivity. This localized quality differentiation resolves the contradiction by allowing each pixel type to operate at its optimal performance level.
2Manufacturing precision
If all pixels are read out in still image mode to maintain high resolution, then image quality is improved, but processing time increases and high-speed operation becomes difficult
Solution Approach 1:
The patent implements dynamic readout control that adapts to different operating modes. In still image mode, all pixels are read out for high quality. In moving image mode, the system dynamically switches to selective readout where only necessary pixels are read out at full resolution while others use thinning, thereby reducing processing time while maintaining adequate quality.
Solution Approach 2:
The patent applies partial readout action by selectively reading out only focus detection pixels at full resolution while using thinning readout for imaging pixels during moving image capture. This partial action approach maintains sufficient image quality while significantly reducing processing time and enabling high-speed operation.
3Measurement precision
If focus detection pixels are arranged at high density to improve detection accuracy, then measurement precision is improved, but device complexity increases due to additional readout circuitry and data processing requirements
Solution Approach 1:
The patent makes the readout control unit universal by enabling it to handle both imaging pixels and focus detection pixels through a single unified control mechanism. This multi-functionality allows the system to switch between different readout strategies (full readout, thinning readout, selective readout) without requiring separate dedicated readout circuits for each pixel type, thereby reducing device complexity while maintaining high detection precision.
Data Source
AI summary
An image capturing apparatus comprises an imaging unit that includes imaging pixels that are arranged in a two-dimensional array and focus detection pixels arranged in part of the array of the imaging pixels, and a control unit that controls to read out pixel signals of imaging lines including the imaging pixels each configured to output a signal used for image generation, and pixel signals of focus detection lines including the focus detection pixels, wherein the control unit changes one of a thinning method and an addition method between the imaging lines and the focus detection lines.