DRSUB

Description

Subtracts a dark-reference band vector from each pixel location of an input data set. The one or more dark-reference band vectors are extracted from a user-specified region of the input data set.

Parameters

Name	Type	Caption	Length	Value range
FILI *	String	Input file name	1 - 192
FILO *	String	Output image file	1 - 192
DBIW *	Integer	Raster input window	4 - 4	Xoffset, Yoffset, Xsize, Ysize
DRTYPE	String	Dark-reference type	0 - 6	LINE | GLOBAL Default: GLOBAL
REPORT	String	Report mode	0 - 192	Quick links
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILI

Specifies the name of the file containing the image data set to modify.

FILO

Specifies the name of the output file to receive the dark-reference transformed image data. The specified file must not exist prior executing DRSUB; otherwise, the function will report an error.

DBIW

Specifies a rectangular window (Xoffset, Yoffset, Xsize, Ysize) that is read from the input image. If this parameter is not specified, the entire image is processed by default.

Xoffset, Yoffset define the upper-left starting pixel coordinates of the window. Xsize is the number of pixels that define the window width. Ysize is the number of lines that define the window height.

DRTYPE

Specifies the type of dark-reference band vector.

REPORT

Specifies where to direct the generated report.

Available options are:

• TERM: generates a report on the terminal (default)
• DISK: generates a report on file "IMPRPT.LST"
• OFF: turns off report generation
• <filename>: appends a report to the specified file

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

• ON: Turns the monitor ON (default)
• OFF: Turns the monitor OFF (recommended if running in batch or background mode)

Details

A region of an image may contain a region of pixel values generated at certain intervals during data acquisition, when the sensor detectors were deliberately shielded from radiation; this is called a dark-reference image region. In the case of whiskbroom sensors, such a region commonly occupies an along-column strip close to one edge of the image. Pixel values in this region represent a sample of an additive contribution to the pixel values everywhere in the image from a non-scene origin. This contribution must be subtracted from the pixel values for them to be proportional to at-sensor radiance.

The user specifies a rectangular window that contains all or part of the dark-reference region using the Dark-Reference Window (DBIW) parameter.

DRSUB derives one or more band vectors from the dark-reference region and subtracts one of these band vectors from the image at each pixel location in the region (the image at a given pixel location is treated as a band vector that coincides with the dark-reference band vector).

If the dark-reference type (DRTYPE) is specified as "LINE", one dark-reference band vector is computed for each scanline that crosses the dark-reference image region. The dark-reference band vector for a scanline is computed as the average of the dark-reference image band-vectors located at pixels included in that scanline. That dark-reference band vector is subtracted from the image band-vector at each pixel on the scanline. Image band-vectors at pixel locations on a scanline that does not cross the dark-reference region are not modified.

If the dark-reference type (DRTYPE) is specified as "GLOBAL", one dark-reference band vector is computed as the average of the image band-vectors at all dark-reference region pixels. This one dark-reference band vector is subtracted from the image band-vector at each pixel in the image.

Example

The following example subtracting a dark-reference band vector from each pixel location of an input data set.

EASI>fili	=	'drsub.pix'	    ! input file name
EASI>filo	=	'output.pix'	! will be created
EASI>dbiw	=	512, 0, 10, 600
EASI>drtype	=	'line'    

EASI>RUN DRSUB

Acknowledgements

PCI Geomatics received financial support from the Canadian Space Agency/L'Agence Spatiale Canadienne through the Earth Observation Application Development Program (EOADP) for the development of this software, under contract 9F028-0-4902/12.