Row-Level Gain Control for High Dynamic Range Imaging

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Solution Overview

Problem

Conventional image sensors face challenges in capturing high dynamic range scenes due to fixed conversion gain, leading to noisy, under-exposed, or saturated image signals, especially when dealing with varying luminance across an image frame, and existing methods to address this often reduce frame rate or introduce artifacts.

Innovation Solution

The implementation of a gain control circuit on-chip within the image sensor that dynamically adjusts pixel gain based on statistical analysis of pixel data, allowing rows of pixels to operate in high or low conversion gain mode as needed, thereby maintaining high dynamic range without reducing frame rate or introducing artifacts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fixed conversion gain is applied to the entire image frame, then the device complexity is reduced, but the dynamic range performance deteriorates in scenes with varying luminance

Engineering Contradiction:

Improvegain control structureVSAvoiddynamic range performance

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The image sensor divides the pixel array into multiple rows, each capable of independent gain control. The gain control circuit receives pixel data from different rows and applies row-specific conversion gains based on the luminance characteristics of each row, allowing different parts of the image to be optimized for their respective lighting conditions

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each row of pixels is assigned a specific conversion gain value that is locally optimized for that row's luminance range. Brighter rows use lower gain while darker rows use higher gain, allowing each local region to operate at optimal sensitivity without affecting other regions

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the entire frame operates in high gain mode to capture dark regions, then the sensitivity to low light is improved, but brighter portions become saturated

Engineering Contradiction:

Improvelow light sensitivityVSAvoidsignal saturation

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The conversion gain parameter is dynamically adjusted for each row based on its luminance characteristics. Rows capturing dark regions operate in high gain mode to amplify weak signals, while rows capturing bright regions operate in low gain mode to prevent saturation, with the gain value selected from at least two different conversion gains

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If the entire frame operates in low gain mode to capture bright regions, then the saturation resistance is improved, but darker portions become noisy and under-exposed

Engineering Contradiction:

Improvesaturation resistanceVSAvoiddark region signal quality

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The conversion gain parameter is dynamically adjusted for each row based on its luminance characteristics. Rows capturing bright regions operate in low gain mode to maintain headroom and prevent saturation, while rows capturing dark regions operate in high gain mode to amplify weak signals and improve signal-to-noise ratio

Inventive Principle:

Principle #35Parameter changes

4Adaptability or versatility

If dual images are captured in different gain modes to achieve high dynamic range, then the dynamic range performance is improved, but the frame rate is reduced by a factor of two

Engineering Contradiction:

Improvedynamic range capabilityVSAvoidframe rate

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

Instead of capturing separate images at different gain modes, the system periodically switches gain modes for different rows within a single frame exposure. This allows simultaneous capture of high and low gain data across different spatial regions, maintaining full frame rate while achieving high dynamic range

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

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

This approach enables improved dynamic range imaging without reducing frame rate, by dynamically adjusting pixel gain, thus capturing a wide range of luminance levels effectively and reducing noise and saturation issues.

Implementation Method 1

Each pixel includes a photosensor, such as a photogate, photoconductor, or photodiode, for accumulating photo-generated charge

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS9854186B2Methods and apparatus for an images sensor with row-level gain control

Publication Date: 2017.12.26 SEMICON COMPONENTS IND LLC

AI summary

Various embodiments of the present technology may comprise methods and systems image sensors. The methods and systems may comprise selectively activating either high or low conversion gain mode for a predetermined number of rows by comparing pixel row data to predetermined threshold values prior to image signal processing.