Color Filter Array Reference Pixel Spectral Crosstalk
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Solution Overview
Problem
Spectral crosstalk in image sensors with color filter arrays leads to degradation of spatial resolution, color mixing, and increased image noise, affecting the signal-to-noise ratio, as existing methods to reduce crosstalk either fail to address the inherent material properties or compromise signal strength and quantum efficiency.
Innovation Solution
Incorporating a reference pixel with a reference filter in the color filter array that transmits similar percentages of light across wavelengths, allowing for the adjustment of imaging pixel values to correct spectral crosstalk by subtracting the reference pixel value, thereby reducing spectral crosstalk without compromising signal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If thicker color filters are used to reduce spectral crosstalk, then spectral crosstalk is reduced, but signal strength and quantum efficiency are reduced
Solution Approach 1:
The patent segments the color filter array into two distinct types of pixels: color pixels with wavelength-selective filters for capturing color information, and reference pixels with broadband filters for capturing total light intensity. This segmentation allows each pixel type to specialize in its function, with reference pixels measuring the sum of all wavelengths that can then be used to correct crosstalk in color pixels through post-processing, rather than requiring all pixels to use thick filters that would reduce signal strength.
Solution Approach 2:
The reference pixels act as an intermediary measurement mechanism. By capturing the total light intensity across all wavelengths, they provide a reference signal that mediates the correction of spectral crosstalk in the color pixels. This intermediary approach allows the system to measure and compensate for crosstalk without requiring the color pixels themselves to have perfect spectral isolation, thereby maintaining signal strength.
2Object-affected harmful factors
If pigment concentration in filters is increased to reduce spectral crosstalk, then spectral crosstalk is reduced, but refractive index increases and induces higher optical crosstalk
Solution Approach 1:
The patent divides the pixel array into color pixels and reference pixels with different filter characteristics. Color pixels use filters with appropriate pigment concentrations for their specific wavelength selection, while reference pixels use broadband filters that transmit all wavelengths. This segmentation eliminates the need to uniformly increase pigment concentration across all pixels, avoiding the refractive index increase and optical crosstalk that would result.
Solution Approach 2:
The patent changes the filter transmission parameters differently for different pixel types. Instead of using high pigment concentration (high absorption) in all filters, the reference pixels use filters with low absorption across all wavelengths (broadband transmission). This parameter change allows the system to measure total light without introducing the optical crosstalk that would result from high pigment concentration and elevated refractive index.
3Use of energy by moving object
If clear filter is used in filter array to gain sensitivity, then sensitivity is improved, but spectral crosstalk increases
Solution Approach 1:
The patent segments the pixel array into color pixels with wavelength-selective filters and reference pixels with clear broadband filters. This segmentation allows reference pixels to use clear filters for maximum sensitivity without spectral crosstalk, while color pixels use selective filters that inherently provide spectral isolation. The clear filter in reference pixels does not cause crosstalk problems because those pixels are not used for color separation.
Solution Approach 2:
The reference pixels with clear filters serve as an intermediary that measures total light intensity without being affected by spectral crosstalk. Since these pixels capture all wavelengths equally, they provide a reference signal that can be used to mathematically correct the crosstalk in color pixels, allowing the system to use clear filters in reference pixels for sensitivity while maintaining color accuracy through post-processing correction.
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 spectral crosstalk, improving the signal-to-noise ratio and maintaining signal strength by accurately interpolating color values, thus enhancing image quality.
Implementation Method 1
Spectral crosstalk is a problem that occurs in devices that filter separate wavelengths, as do color filters that are coupled to a pixel array in a color image sensor when a small portion of the optical power that should have ended up in a particular channel—that is, that should have been output by particular filter—actually ends up in another channel
Data Source
AI summary
A color filter array includes a plurality of tiled minimal repeating units, each minimal repeating unit comprising an M×N set of individual filters. Each minimal repeating unit includes a plurality of imaging filters including individual filters having at least first, second, and third photoresponses, and at least one reference filter having a reference photoresponse, wherein the reference filter is positioned among the imaging filters and wherein the reference photoresponse transmits substantially the same percentage of wavelengths that remain unfiltered by filters of a different photoresponse than the incident wavelength. Other embodiments are disclosed and claimed.