generation of multispectral filter array

Generation of Multispectral Filter Array

Lidan Miao01/22/04

Motivation Color image (Color filter array).

Sensing the wavelengths in the visible spectrum (400~700nm).

Multispectral image (Multispectral filter array).

CCD sensors can detect light (NIR:700~1100nm) outside the sensitivity of HVS. Additional information can be obtained from these spectral bands.

Objective CFA and MSFA

Each sensor sense one spectral band and the unmeasured spectral bands can be interpolated.

Rectangular array and Hexagonal arrayThe hexagonal grid can model the human visual system more precisely.

Design criteria of CFA

Uniform distribution Equal sample frequency. Color consistency. Spectral sensitivity.

Bayer color filter array

MSFA in the rectangle domain

Breakup algorithm Checkboard pattern

Breakup algorithm Binary tree and MSFA

Characteristics

Symmetrical and uniform distribution. Each band has the same number of

neighbors of certain spectrum and the relative position of different spectra is fixed.

The percentage of each spectrum is determined by the separation process.

(a)Equal Probability

(b)Unequal Probability

MSFA in the hexagon domain(3 methods)

Method 1 Directly apply the algorithm in the rectangle array.

“Checkboard” pattern

Method 2 Apply a new coordinate system.

(a) Coordinate system

Method 2

“Checkboard” pattern

Method 3

Based on the distance between the adjacent pixels.

Each pixel has 4 immediate neighbors (distance =1) and 4 secondary neighbors (distance = sqrt(2)).

For each pixel, half of its neighbors are chosen.

As we increase the distance, the percentage decreases.

Method 3

Limitation Cannot generate all the filter arrays with equal probability.

Rectangular array: 3, 5, 7 bands…

Hexagonal array (method 3): 4, 5, 6, 7 bands… The probability is restrict to 1/2, 1/4, 1/8,…… or 1/3, 2/3,

2/9, 1/9……

Comparison

(a) has all the characteristics in the rectangle domain.

(b) is sensitive to cross talk. (c) has the property of equal distance.

(a) Method 1

(b) Method 2

(c) Method 3

Which one do you like?