This routine is obsolete and has been replaced by the SpectralSubspaceBackgroundStatistics task.

Use this procedure to remove anomalous pixels prior to calculating background statistics with ENVI_ACE_DOIT, ENVI_CEM_DOIT, ENVI_TCIMF_DOIT, ENVI_TCIMF_MT_DOIT, MATCH_FILTER_DOIT, or MATCH_FILTER_MT_DOIT. When the true background is better characterized with subspace background, these spectral detection methods achieve greater target-to-background separation. ENVI_SUBSPACE_BACKGROUND_STATS_DOIT can potentially improve detection results, particularly in scenes that contain a lot of clutter or man-made objects.

Syntax

ENVI_DOIT, 'ENVI_SUBSPACE_BACKGROUND_STATS_DOIT' [, BACKGROUND_THRESH=value] [COV=variable], DIMS=array [, EVAL=variable], FID=file ID [, M_FID=file ID] [, M_POS=value] [, MEAN=variable], POS=array [, STA_NAME=string], STATUS=variable [, XFAC=value] [, YFAC=value]

Keywords

BACKGROUND_THRESH (optional)

Use this keyword to specify the fraction of the background in the anomaly image to use for calculating the subspace background statistics. The data type is floating-point. The allowable range is 0.500 to 1.000 (the entire image). The default is 0.900.

COV (optional)

Use this keyword to specify a named variable that contains the returned covariance matrix of subspace background.

DIMS

The “dimensions” keyword is a five-element array of long integers that defines the spatial subset (of a file or array) to use for processing. Nearly every time you specify the keyword FID, you must also specify the spatial subset of the corresponding file (even if the entire file, with no spatial subsetting, is to be processed).

  • DIMS[0]: A pointer to an open ROI; use only in cases where ROIs define the spatial subset. Otherwise, set to -1L.
  • DIMS[1]: The starting sample number. The first x pixel is 0.
  • DIMS[2]: The ending sample number
  • DIMS[3]: The starting line number. The first y pixel is 0.
  • DIMS[4]: The ending line number

To process an entire file (with no spatial subsetting), define DIMS as shown in the following code example. This example assumes you have already opened a file using ENVI_SELECT or ENVI_PICKFILE:

  envi_file_query, fid, dims=dims

EVAL (optional)

Use this keyword to specify a named variable that contains the eigenvalues of the subspace background.

FID

The file ID (FID) is a long-integer scalar with a value greater than 0. An invalid FID has a value of -1. The FID is provided as a named variable by any routine used to open or select a file. Often, the FID is returned from the keyword R_FID in the ENVIRasterToFID routine. Files are processed by referring to their FIDs. If you work directly with the file in IDL, the FID is not equivalent to a logical unit number (LUN).

M_FID (optional)

Use this keyword to specify the file ID of the mask file. This value is returned from the keyword R_FID in the ENVI_OPEN_FILE procedure. M_FID is a long integer with a value greater than 0. An invalid file ID has a value of -1.

M_POS (optional)

Use this keyword to specify the band position of the mask band. M_POS is a long integer with a value greater than or equal to 0.

MEAN (optional)

Use this keyword to specify a named variable that contains the array of data means of subspace background, one for each band position.

POS

Use this keyword to specify an array of band positions, indicating the band numbers on which to perform the operation. This keyword indicates the spectral subset of bands to use in processing. POS is an array of long integers, ranging from 0 to the number of bands minus 1. Specify bands starting with zero (Band 1=0, Band 2=1, etc.) For example, to process only Bands 3 and 4 of a multi-band file, POS=[2, 3].

POS is typically used with individual files. The example code below illustrates the use of POS for a single file with four bands of data:

  pos=[0,1,2,3]
                  
envi_doit, 'envi_stats_doit', dims=dims, fid=fid, pos=pos, $
                  
comp_flag=3, dmin=dmin, dmax=dmax, mean=mean, stdv=stdv, hist=hist

But what if you need to create an output file consisting of data from different bands, each from different files? Library routines such as CF_DOIT and ENVI_LAYER_STACKING_DOIT can accomplish this, but they use the POS keyword differently. Suppose you have four files, test1, test2, test3, and test4, with corresponding FIDs of fid1, fid2, fid3, and fid4, respectively. In the following example, you want Band 3 from test1 in the first position, Band 2 from test2 in the second position, Band 6 from test3 in the third position, and Band 4 from test4 in the fourth position. The code should be as follows:

  fid_array = [fid1,fid2,fid3,fid4]
                  
pos=[2,1,5,3]
                  
envi_doit, 'cf_doit', dims=dims, fid=fid_array
                  
out_name='test_composite_file'

STA_NAME

Use this keyword to specify the filename for the output subspace background statistics.

STATUS

Use this keyword to return the status of the computation. ENVI Classic returns 0 upon success and -1 upon failure.

XFAC (optional)

Use this keyword to specify an x skip factor for computing statistics. XFAC is a floating-point value greater than or equal to 1.0 (the default). For example, to compute statistics using every 10th pixel, set XFAC=10.

YFAC (optional)

Use this keyword to specify a y skip factor for computing statistics. YFAC is a floating-point value greater than or equal to 1.0 (the default). For example, to compute statistics using every 10th pixel, set YFAC=10.