Dual Gain Image Sensor Floating Diffusion Capacity Control

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Solution Overview

Problem

Dual gain output (DGO) imaging elements face challenges in setting an appropriate floating diffusion (FD) capacity for high and low gain images, leading to increased noise in synthetic images due to shared FD capacity across different sensitivities, making it difficult to achieve optimal noise reduction.

Innovation Solution

An image processing device with an imaging element that includes a pixel unit with a photoelectric conversion unit and a charge accumulating unit, an image synthesizing unit, and an image synthesis control unit to determine synthesis proportions based on a common FD capacity, allowing for controlled noise reduction by adjusting synthesis threshold values and FD capacity settings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the FD capacity is increased to process more light, then the light processing capability is improved, but the noise increases

Engineering Contradiction:

Improvelight processing capabilityVSAvoidnoise

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent divides the imaging element into multiple pixel units, each with its own floating diffusion unit having different capacities. This segmentation allows different regions to have different FD capacities optimized for their specific light processing requirements, preventing the noise increase that would occur if a single large FD capacity was used across the entire sensor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each pixel unit is assigned a specific FD capacity according to its local requirements. The control unit sets different FD capacities for different pixel units based on the image content and processing needs, allowing optimal noise performance in each region while maintaining overall light processing capability.

Inventive Principle:

Principle #3Local quality

2Device complexity

If the FD capacity is shared by high gain and low gain images, then the device complexity is reduced, but the appropriate FD capacity cannot be set for some sensitivity combinations

Engineering Contradiction:

ImproveFD capacity configurationVSAvoidFD capacity setting precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent implements dynamic control of FD capacities through a control unit that can adjust the capacity of each floating diffusion unit independently based on the gain settings and image processing requirements. This dynamic adjustment allows the system to optimize FD capacity for each pixel unit in real-time, resolving the contradiction between simplicity and precision.

Inventive Principle:

Principle #15Dynamics

3Object-affected harmful factors

If a small FD capacity is used at high ISO speed, then the noise is reduced, but the FD capacity becomes insufficient and the FD is saturated

Engineering Contradiction:

ImprovenoiseVSAvoidFD capacity sufficiency

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

By segmenting the sensor into multiple pixel units with independent FD capacity control, the system can use small FD capacities in regions where high ISO speed processing is needed (to reduce noise) while using larger FD capacities in regions where light processing capability is prioritized (to prevent saturation). This eliminates the binary choice between noise reduction and capacity sufficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control unit dynamically changes the FD capacity parameter for each pixel unit based on the operating conditions, including ISO speed settings and image content analysis. This allows the system to adapt the FD capacity to match the processing requirements, preventing both noise and saturation issues.

Inventive Principle:

Principle #35Parameter changes

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

The solution effectively reduces noise in synthetic images by optimizing FD capacity settings and synthesis threshold values, improving the signal-to-noise ratio and dynamic range of images captured with dual gain outputs.

Implementation Method 1

a pixel unit including a photoelectric conversion unit configured to convert light to electric charge

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

a charge accumulating unit configured to accumulate the electric charge

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11778346B2Image processing device, image processing method, and storage medium

Publication Date: 2023.10.03 CANON KK

AI summary

An image processing device includes an imaging element. The imaging element includes a pixel unit including a photoelectric conversion unit configured to convert light to electric charge and a charge accumulating unit configured to accumulate the electric charge and a column AMP configured to amplify a signal output from the pixel unit with different gains, and outputs a plurality of image signals with different gains applied thereto through one exposure. The image processing device further includes an image synthesizing unit configured to generate a synthetic image signal by synthesizing the plurality of image signals. An image synthesis control unit configured to control the image synthesizing unit determines synthesis proportions of the plurality of image signals in the synthetic image signal according to a common capacity of the charge accumulating unit when the capacity of the charge accumulating unit is shared by the plurality of image signals.