This task uses pre-defined thresholding techniques to automatically classify change detection between two images.
Example
This example performs a difference analysis between two images from different dates, then it performs automatic thresholding for change detection. The images represent NCEP-Reanalysis 2 air temperatures (K) at the 1000-isobar level, at 0600 hours Zulu time. The first image is from 29 December 2012, and the second is from 31 December 2012. Each image has one band. This example uses sample data from the ENVI installation path.
e = ENVI()
TimeSeriesDir = Filepath('', Subdir=['data','time_series'], $
Root_Dir = e.Root_Dir)
files = File_Search(TimeSeriesDir, 'AirTemp*.dat')
numRasters = N_Elements(files)
rasters = ObjArr(numRasters)
FOR i=0, (numRasters-1) DO $
rasters[i] = e.OpenRaster(files[i])
Task = ENVITask('BuildTimeSeries')
Task.INPUT_RASTERS = rasters
Task.Execute
SeriesFile = Task.OUTPUT_RASTERSERIES
SeriesFile.Set, 0
Image1 = SeriesFile.Raster
SeriesFile.Set, 8
Image2 = SeriesFile.Raster
Task = ENVITask('ImageBandDifference')
Task.INPUT_RASTER1 = Image1
Task.INPUT_RASTER2 = Image2
Task.Execute
AutoChangeThreshTask = ENVITask('AutoChangeThresholdClassification')
AutoChangeThreshTask.INPUT_RASTER = Task.OUTPUT_RASTER
AutoChangeThreshTask.Execute
DataColl = e.Data
DataColl.Add, AutoChangeThreshTask.OUTPUT_RASTER
View = e.GetView()
Layer = View.CreateLayer(AutoChangeThreshTask.OUTPUT_RASTER)
Syntax
Result = ENVITask('AutoChangeThresholdClassification')
Input parameters (Set, Get): CHANGE_TYPE, INPUT_RASTER, OUTPUT_RASTER_URI, THRESHOLD_METHOD
Output parameters (Get only): OUTPUT_RASTER
Parameters marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Parameters marked as "Get" are those whose values you can retrieve but not set.
Input Parameters
CHANGE_TYPE (optional)
Specify the change of interest:
- Both (default): Shows areas of increase (in blue) and decrease (in red).
- Increase: Shows areas of increase (in blue) only.
- Decrease: Shows areas of decrease (in red) only.
INPUT_RASTER (required)
Specify a raster on which to threshold.
OUTPUT_RASTER_URI (optional)
Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER.
- If you do not specify this parameter, or set it to an exclamation symbol (!), ENVI creates a temporary file.
- If you set it to the hash symbol (#), ENVI creates a file in the temporary directory, but this file will not be deleted when ENVI closes.
THRESHOLD_METHOD (optional)
Specify the thresholding method.
- Otsu (default): A histogram shape-based method that is based on discriminate analysis. It uses the zero- and first-order cumulative moments of the histogram for calculating the value of the thresholding level.
- Tsai: A moment-based method. It determines the threshold so that the first three moments of the input image are preserved in the output image.
- Kapur: An entropy-based method. It considers the thresholding image as two classes of events, with each class characterized by a Probability Density Function (PDF). The method then maximizes the sum of the entropy of the two PDFs to converge on a single threshold value.
- Kittler: A histogram shape-based method. It approximates the histogram as a bimodal Gaussian distribution and finds a cutoff point. The cost function is based on the Bayes classification rule.
Output Parameters
OUTPUT_RASTER
This is a reference to the output raster of filetype ENVI.
Methods
Execute
Parameter
ParameterNames
Properties
DESCRIPTION
DISPLAY_NAME
NAME
REVISION
TAGS
Version History
See Also
ChangeThresholdClassification Task, Masking Support in ENVITasks