Rolling Shutter Imager Flicker Detection for Autofocus

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Solution Overview

Problem

CMOS image sensors with rolling shutters face image quality degradation due to flickering light sources, as the varying light intensity affects each photodiode differently, leading to inconsistent contrast and interfering with autofocus processes.

Innovation Solution

An imager system comprising an image-capturing sensor, a focusing detector, and a flicker detector that uses horizontal data from the image data to determine focus without vertical data when flicker is detected, employing a flicker reduction procedure to stabilize contrast autofocus under flickering conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a rolling shutter is used to capture images, then the image capture speed is improved, but image quality deteriorates under flickering light conditions due to varying exposure moments across photodiodes

Engineering Contradiction:

Improveimage capture speedVSAvoidimage quality

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent segments the image data into horizontal and vertical components. By using only horizontal data (data from the same horizontal position across different rows) for focus determination, it eliminates the vertical dimension where flicker-induced variations occur, while maintaining the rolling shutter's speed advantage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by selectively using horizontal data from specific positions in the image for focus determination. This localized approach ensures that only the necessary data (horizontal comparisons) are used, avoiding the quality degradation caused by vertical data under flickering conditions.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If contrast AF uses both horizontal and vertical data, then the focusing accuracy is improved, but the system becomes vulnerable to flicker interference

Engineering Contradiction:

Improvefocusing accuracyVSAvoidflicker interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts only the horizontal component of image data for focus determination, removing the vertical component that contains flicker-induced variations. This extraction maintains focusing accuracy through horizontal contrast comparison while eliminating vulnerability to flicker interference.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the parameter used for focus determination from both horizontal and vertical data to only horizontal data. This parameter change maintains the ability to measure focus accuracy while making the system immune to flicker effects that manifest in the vertical dimension.

Inventive Principle:

Principle #35Parameter changes

3Power

If all photodiodes are used for focus determination, then the signal strength is improved, but the contrast becomes inconsistent under varying light intensity

Engineering Contradiction:

Improvesignal strengthVSAvoidcontrast consistency

Core Design Contradiction:

PowerVSStability of the object's composition

Solution Approach 1:

The patent segments the data usage by photodiodes, having each photodiode contribute only its horizontal data for focus determination. This segmentation maintains signal strength through collective horizontal comparisons while ensuring contrast consistency by eliminating vertical variations caused by flicker.

Inventive Principle:

Principle #1Segmentation

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

Enables accurate focus on a subject using contrast autofocus even under flickering light conditions by mitigating the effects of varying light intensity across photodiodes, ensuring consistent image quality.

Implementation Method 1

a plurality of photodiodes... the moment of exposure is different for each photodiode in the vertical direction because a CMOS image sensor photographs with a rolling shutter

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

The flicker detector detects a flicker in the output image data

Methodology Applied

Scientific EffectFlicker detection:

Data Source

PatentUS8681263B2Imager capturing an image with a rolling shutter using flicker detection

Publication Date: 2014.03.25 RICOH IMAGING COMPANY

AI summary

An imager is provided having an image-capturing sensor, a focusing detector, and a flicker detector. The image-capturing sensor captures a subject image with a rolling shutter and outputs image data. The focusing detector determines whether a subject image is in focus of the image-capturing sensor using the output image data. The flicker detector detects a flicker in the output image data. The focusing detector uses horizontal data without vertical data from the image data so as to determine whether a subject image is in focus, when the flicker detector detects a flicker.