LACD

Description

LACD calculates a difference image from two input images.

Parameters

Name	Type	Length	Value range
Input2: Input reference channels *	Raster port	1 - 1
Input: Input raster image channel *	Raster port	1 - 1
Output: Output difference channel *	Raster port	1 - 1
Kernel Size	Integer	0 - 1	1 - Default: 7
Resample Mode	String	0 - 1	Near | Bilinear | Cubic Default: Near

* Required parameter

Parameter descriptions

Input2: Input reference channels

Specifies the input reference image channel from the reference image file.

The reference image channel must be the same size and datatype (8-bit unsigned) as the input raster channel (DBIC_IN).

Input: Input raster image channel

Specifies the input raster image channel from the input file.

This image channel must be the same size and datatype (8-bit unsigned) as the reference image channel (DBIC_REF).

Output: Output difference channel

Specifies the output image channel to receive the Local Adaptive Change Detection data.

The output difference channel must be the same size as the input channel (DBIC_IN) and the input reference channel (DBIC_REF). The output channel datatype must be 32-bit real (32R).

Kernel Size

Specifies the size of the square kernel M x M over which the local coefficients of b0 and b1 are determined, where M=(2*KSIZE+1).

The size of M defines the upper boundary of the size of the change that will be detected. The length of time to compute is linearly proportional to M**2.

Resample Mode

Specifies the resampling method to use in evaluating the output image pixel values.

Details

LACD performs a change detection comparison of two input images, and writes the output to a 32-bit real image of the same size. Input is restricted to 8-bit unsigned images, of the same X/Y (pixels and lines) dimensions.

LACD performs its change detection on a localized scale. The least-squares minimization parameters, B0 and B1, are calculated using local windows of data specified by the Kernel Size (KSIZE). The formula for the difference calculation is the same as for GCD, except that the B0 and B1 parameters change with each pixel:

FILI_DIF = Minimize || FILI_IN - (B1 * FILI_REF + B0) ||

Algorithm

Local Adaptive Change Detection obtains a difference image from two input images, I1 and I2, by the the following formula:

I1 -  (b1 * I2 + b0)            (1)

The coefficients, b0 and b1, were calculated by using Least Square Minimization; for example:

Min || I1 -  (b1 * I2 + b0) ||  (2)

The coefficients b0 and b1 are calculated locally from a sequence of sliding M x M windows, pixel by pixel, where M = 2*KSIZE + 1. Equation (1) is then applied to obtain the difference image of M x M locally.

References

Jack S. Li, (Revised by Victor Tom and Stephen Bento), 1996. "Local Adaptive Change Detection, Atlantic Aerospace Electronic Corporation", Waltham, MA , USA.