The Stretch operation re-distributes values of an input map over a wider or narrower range of values in an output map. Stretching can for instance be used to enhance the contrast in your map when it is displayed. Two stretch methods are available: linear stretching and histogram equalization.
Dialog box options:
Input raster map: |
Select an input raster map or an input map list. Open the list box and select the desired input map or map list, or directly drag a raster map or map list from a Catalog into this box. The input map(s) must be value map(s). When you select an input map list, the operation will be performed on all raster maps in the map list. |
Method: |
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Intervals: |
For histogram equalization: specify the number of output intervals. When 256 intervals are specified, the output values will range from 0 to 255; when another number of output intervals is specified, the first interval will obtain output value 1, the second value 2, etc. |
Stretch from: |
Specify the range of input values to be stretched. |
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Enter lower and upper values to define the range of input values that will be stretched. |
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Enter a percentage of pixels not to be taken into account by during stretching. When entering for instance 1%, this means that 1% of the smallest values in the map and 1% of the largest values in the map are ignored. |
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Output raster map: |
Type a name for the output raster map that will contain the stretched values. If you selected an input map list, then you can type a name for the output map list; all raster maps in the output map list will obtain this name followed by _1, _2, _3, etc. |
Domain: |
For linear stretching: select an existing value domain for the output map(s).
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Value range: |
For linear stretching with an output value domain but not domain Image: adjust these values to the values to which you want to stretch to. |
Precision: |
For linear stretching with an output value domain but not domain Image: adjust the precision if you want to change the 'resolution' of possible values in the output map. |
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Description: |
Optionally, type a description for the output map or the output map list. The description will appear in the status bar of the Main window when moving the mouse pointer over the map in a Catalog, and in the title bar of a map window when the output map is displayed. If no description is supplied, the output map or the output map list will use its own definition as description. |
When you selected a single raster map as input:
When you selected a map list as input:
The output map(s) are always value map(s). For histogram equalization, the output domain is always a value domain, and the 'stretch to' value range is determined from the number of specified intervals.
See also: