Color Filter Array With Wide Band Pass for Low Light Sensitivity

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Solution Overview

Problem

Conventional Bayer color filters in image sensors have low light sensitivity due to their narrow band-pass nature, which becomes a significant issue in low light conditions, and they fail to accurately capture fine details and object edges, leading to artifacts like aliasing.

Innovation Solution

A color filter array with two narrow band filters and one wide band filter, along with a method for processing tri-stimulus signals to dynamically adjust color contrast based on illumination conditions, increasing the sensitivity of image sensors without expanding their photosensitive area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If narrow band-pass color filters are used in conventional Bayer pattern, then color image capture is enabled, but low light sensitivity is reduced

Engineering Contradiction:

Improvelow light sensitivityVSAvoidcolor accuracy

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

The filter array is segmented into multiple types of filters (first narrow band-pass, second narrow band-pass, and wide band-pass) arranged in a specific pattern. This segmentation allows different regions to capture different portions of the light spectrum, with the wide band-pass filters capturing broader light including low light conditions, while narrow band-pass filters maintain color accuracy for their respective color channels.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different filters are placed at different locations in the array with specific properties: narrow band-pass filters at certain positions for color precision, and wide band-pass filters at other positions for light sensitivity. This local differentiation optimizes both color accuracy and low light performance in different regions of the sensor array.

Inventive Principle:

Principle #3Local quality

2Illumination intensity

If photosensitive area is increased to improve sensitivity, then low light sensitivity increases, but device size increases

Engineering Contradiction:

Improvelow light sensitivityVSAvoidsensor area

Core Design Contradiction:

Illumination intensityVSArea of stationary object

Solution Approach 1:

The filter array structure enables each sensor element to serve multiple functions through the combination of different filter types. The wide band-pass filters allow individual pixels to capture broader spectrum light for improved sensitivity, while the integrated pattern maintains color information capture, making each pixel more versatile without increasing physical size.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

Instead of increasing the photosensitive area in two dimensions, the invention adds a spectral dimension by incorporating wide band-pass filters that capture broader wavelength ranges. This dimensional approach to light capture improves sensitivity without expanding the physical footprint of the sensor array.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of operation

If conventional Bayer interpolation is used, then color images are produced from single-color pixel data, but aliasing artifacts occur at edges and fine details

Engineering Contradiction:

Improvecolor image productionVSAvoidedge detail accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The filter array is configured in advance with a specific repeating pattern of narrow and wide band-pass filters that captures both color and luminance information more effectively. This preliminary structural arrangement reduces the need for aggressive interpolation and minimizes aliasing artifacts before image processing begins.

Inventive Principle:

Principle #10Preliminary action

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 enhances low light sensitivity and reduces artifacts by allowing the image sensor to capture the entire visible spectrum, improving image quality under various illumination conditions without increasing the sensor's area.

Implementation Method 1

The color filter has a first narrow band-pass filter, a second narrow band-pass filter, and a wide band-pass filter

Methodology Applied

Scientific EffectWide band-pass filtering: Filter (optical)

Implementation Method 2

Each of the pixel sensor cells 22 has a photosensitive element 12, which may be any photon-to-charge converting device

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS7477304B2Two narrow band and one wide band color filter for increasing color image sensor sensitivity

Publication Date: 2009.01.13 MICRON TECHNOLOGY INC

AI summary

A color filter to increase the low light sensitivity of an image sensor. The color filter has two narrow band color filters and one wide band filter. Also disclosed is a unique way of processing a tri-stimulus signal to dynamically adjust color contrast depending on the illumination conditions.