Setting up change detection

You set up change detection by selecting a working raster, reference raster, and, if necessary, layer values for each.

Note: It is recommended that you read Performing change detection before proceeding.

To set up change detection

On the Analysis menu, click Change Detection.
The Change Detection window appears.
On the Setup tab, under Working raster (A), type the full path and file name of the recent image you want to use in the File box, or click Browse to select the file.
- In the Layer list, click the layer of the working raster you want to use.
  - All: Each layer (or channel) in the file will be used
  - <Layer/channel_name>: Only the specified layer (or channel) will be used
  Note: You must select the same number of channels for the reference raster.
Under Reference raster (B), type the full path and file name of the recent image you want to use in the File box, or click Browse to select the file.
- In the Layer list, click the layer of the reference raster you want to use.
  - All: Each layer (or channel) in the file will be used as input data
  - <Layer/channel_name>: Only the specified layer (or channel) will be used
  Note: The number of channels must be the same as the working raster.
In the Algorithm list, click the method of comparison you want to use:
- Difference (A-B): Subtracts pixels in the reference raster from the working raster
- Ratio (A/B): Divides pixels in the working raster by those in the reference raster
If you want to use absolute value of the computed change layer, select the Absolute value check box.
If you want to use a consistent scale regardless of the input-pixel values, select the Percentile check box.
In the Output Display list, click the type of display to use for your output:
- RGB: Maps red to the working layer (A), green to the reference layer (B), and blue to the change layer
- Pseudocolor: Displays the computed change layer using a default PCT
- Grayscale: Displays the computed change layer using a default LUT
If you want to remove a change layer that was already computed and replace it with the new output, select the Overwrite previous results check box.
This check box is available only when a previous change detection was created and appears on the Map tab as a temporary layer.
If you are ready to perform the change detection, click Run; otherwise, if you want to specify masks to control which pixels are considered, click the Masks tab.
Note: For the Run button to be available, a file and layer value for both the working and reference raster must be specified.

For information on completing the Masks tab, see Using an inclusion mask, exclusion mask, or both