WO2022185345A2 - Réseau de filtres colorés optimal et son procédé de démosaïquage - Google Patents

Réseau de filtres colorés optimal et son procédé de démosaïquage Download PDF

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Publication number
WO2022185345A2
WO2022185345A2 PCT/IN2022/050667 IN2022050667W WO2022185345A2 WO 2022185345 A2 WO2022185345 A2 WO 2022185345A2 IN 2022050667 W IN2022050667 W IN 2022050667W WO 2022185345 A2 WO2022185345 A2 WO 2022185345A2
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Prior art keywords
color
image
cfa
color filter
image sensor
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Application number
PCT/IN2022/050667
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English (en)
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WO2022185345A3 (fr
WO2022185345A4 (fr
Inventor
Shantanu Singh
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Shantanu Singh
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Publication of WO2022185345A2 publication Critical patent/WO2022185345A2/fr
Publication of WO2022185345A3 publication Critical patent/WO2022185345A3/fr
Publication of WO2022185345A4 publication Critical patent/WO2022185345A4/fr

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T3/00—Geometric image transformations in the plane of the image
    • G06T3/40—Scaling of whole images or parts thereof, e.g. expanding or contracting
    • G06T3/4015—Image demosaicing, e.g. colour filter arrays [CFA] or Bayer patterns
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/10—Circuitry of solid-state image sensors [SSIS]; Control thereof for transforming different wavelengths into image signals
    • H04N25/11—Arrangement of colour filter arrays [CFA]; Filter mosaics
    • H04N25/13—Arrangement of colour filter arrays [CFA]; Filter mosaics characterised by the spectral characteristics of the filter elements
    • H04N25/134—Arrangement of colour filter arrays [CFA]; Filter mosaics characterised by the spectral characteristics of the filter elements based on three different wavelength filter elements

Definitions

  • Optimal color filter array and a demosaicing method thereof [0001] A method for capturing raw image data for a full-color image by a digital image sensor is provided having a color filter array (CFA), the color filter elements of which may transmit a combination of plural colors, unlike conventional CFAs which allow only one color per color filter element.
  • CFA color filter array
  • An image demosaicing method for demosaicing the color information is described in detail.
  • the field of present invention is color filter array (CFA).
  • CFA color filter array
  • the present invention provides a method to capture accurate color information with improved light sensitivity, and a demosaicing method to generate full color image from the captured color information which exhibit better image quality and lower computational complexity over conventional methods and systems.
  • image sensors comprise an array of photosensitive pixels that are often arranged in a regular pattern of minimum repeat units.
  • a color filter array pattern is typically fabricated on the pixel array to capture color information, in which case different filter elements are associated with different color-channels.
  • the color filters inevitably reduces the amount of light reaching each pixel, thereby reducing the photosensitivity of each pixel.
  • Image demosaicing (also color reconstruction) is an image processing stage to convert the raw image data received from image sensor into into full color RGB data by interpolation.
  • the semiconductor imaging sensor available in digital color cameras is a grayscale sensor that is not capable of detecting different colors.
  • a color filter array is overlaid the semiconductor imaging sensor.
  • the CFA is a grid of color filters overlaying the imaging sensor so that each sensor element receives light corresponding to a single color component. In this way a mosaic image is captured where image elements have intensity value for one of three or more color channels (Red, Green and Blue for example).
  • Demosaicing is a process whereby intensity values for the other two channels are estimated for each of the image elements.
  • the present disclosure relates to color filter arrays. More specifically, and without limitations, this disclosure relates to a method for capturing color information via a digital pixel image sensor equipped with a CFA and demosaicing of the raw image sensor data to obtain a full-color image.
  • the method includes a CFA, color filter elements of which may transmit a combination of plural different colors, unlike most conventional CFAs that allow image elements to store intensity values in one of three or more color channels (Red, Green and Blue for example).
  • the raw image data captured by the image sensor may be deemed a superposition of arrays of pixel values of plural color components instead of discrete arrays of pixel values, each indicating a raw intensity of one of the component colors.
  • the disclosure also describes, inter alia, a demosaicing method, adapted to reconstruct a full color image from the color information obtained via image sensor overlaid with the new CFA.
  • the raw image data obtained by described digital image sensor is represented as systems of linear equations inN variables, wherein theN is number of color components in color model being used.
  • the demosaicing method for each particular pixel represented in the CFA data, calculates a new value for the particular pixel by passing pixel values of all pixels in the minimum repeat unit through an algorithm.
  • an improved version of the Bayer CFA is provided.
  • the new CFA has the special feature that each color filter element in the CFA pattern transmits a combination of the three RGB colors. This is unlike Bayer CFA which transmit a single component of RGB colors for each color filter element.
  • the light intensity transmitted through the new CFA over underlying pixel group is significantly increased, thereby improving light sensitivity of image sensor.
  • a special demosaicing method is provided for transforming the input pixel values to the corresponding output RGB color values.
  • this example can be further generalized to all the other known CFA patterns and may be used in further research studies.
  • the demosaicing process reconstructs a full-color image from incomplete color samples output from an image sensor overlaid with a CFA by estimating the missing color values for each pixel in a raw capture (see, for example, Guenter US20040001641A1). This is required due to the fact that most raw captures record a single color value for each image pixel.
  • demosaicing does not specifically address fundamental undersampling in typical camera designs.
  • An object of this invention is to capture color information at a lower expense of intensity of incoming light than conventional CFAs.
  • Method presented herein allows for determination of spectral transmittance of each color filter element in the CFA pattern corresponding to maximum intensity of light transmitted through the CFA.
  • the supplemental incoming light enhances light sensitivity.
  • the centerpiece of this invention is that the increase in incident light intensity as well as the following demosaicing operation requires no additional compromise on image quality, and that the manufacturing can be carried out at no extra cost and complexity.
  • a sensor pixel is representable by the matrix equation
  • matrices denote intensity of different color components c k of the color model being used in the incident light, color filter transmittance corresponding to each color component c k , the pixel intensity value, respectively; and is the quantization function for transforming the input original image data to quantized image data. Since each photosite produce an electrical charge directly proportional to the light intensity it receives with no wavelength specificity, arc independent variables.
  • J axa is also the variable matrix representing color information about the pixel group.
  • C 1 xN can be determined by solving Equation (1) using Cramer’s rule (see Azamat, Akhtyamov, et al.) under condition that total number of unique F i,j ⁇ H axb (representing independent linear equations) are equal to or greater than N (total number of unknown variables ) ⁇
  • a full-color image can be obtained by applying any known demosaicing method to matrix P axb , which is defined by the conditional statement
  • Optimal H aXb corresponding to a desired spectral responses can be formulated through computational methods by substituting the spectral responses into C 1 xN , and then solving Equation (1) for H aXb to maximize ⁇ i,j P i,j .
  • R,G,B are desired spectral responses of Bayer filter as shown in FIG. 1, wherein
  • F 1,1 the actual spectral transmission characteristic of F 1,1 , defined as , is obtained by applying min-max normalization method to perform [0, 1] norma lization on , as shown in FIG. 2. Therefore, F 1,2 can be calculated by using the following formula:
  • the light intensity transmitted through the CFA pattern on underlying pixel group is which is equivalent to about 148% as much light sensitivity as available via the Bayer filter.
  • the final RGB color values in C 1 x3 are based on weighted average of RGB pixel values of all pixels of the minimum repeat unit, and thus color accuracy and color consistency in final full-color image is better than when measured by Bayer image sensor, wherein each color component value is measured at a single camera-sensor pixel location, and then interpolated for neighboring pixels.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Color Television Image Signal Generators (AREA)

Abstract

L'invention concerne un procédé permettant de capturer des données d'image couleur numérique, un ou plusieurs éléments de filtre coloré dans un motif de réseau de filtres colorés (CFA) constituant un mélange optique d'au moins deux filtres colorés, chacun étant conçu pour transmettre une composante de couleur unique. Les données de capteur d'image brute obtenues comprennent des éléments d'image présentant des valeurs d'intensité dans plusieurs canaux de couleur. Ceci est différent des réseaux CFA classiques, chaque élément d'image dans des données de capteur d'image brute présentant une valeur d'intensité dans l'un des canaux de couleur (rouge, vert ou bleu par exemple). Les données d'image de capteur finales peuvent être considérées comme un compromis entre l'image couleur et l'image d'échelle de gris. Un procédé de démosaïquage d'image de réseau CFA est décrit pour convertir des données de capteur d'image brute où des éléments d'image présentent une valeur d'intensité d'échelle de gris en une image en couleur pleine où des éléments d'image présentent des valeurs d'intensité réelle dans tous les canaux de couleur.
PCT/IN2022/050667 2022-07-18 2022-07-25 Réseau de filtres colorés optimal et son procédé de démosaïquage WO2022185345A2 (fr)

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IN202211041012 2022-07-18
IN202211041012 2022-07-18

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WO2022185345A2 true WO2022185345A2 (fr) 2022-09-09
WO2022185345A3 WO2022185345A3 (fr) 2022-11-10
WO2022185345A4 WO2022185345A4 (fr) 2022-12-01

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Publication number Priority date Publication date Assignee Title
US9071721B1 (en) * 2012-12-21 2015-06-30 Google Inc. Camera architecture having a repositionable color filter array

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WO2022185345A3 (fr) 2022-11-10
WO2022185345A4 (fr) 2022-12-01

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