THR

Description

THR creates bitmaps from image channels, including complex channels, given minimum and maximum threshold values.

Parameters

Name	Type	Length	Value range
Input: Input raster channel *	Raster port	1 - 1024	-1024 -
OutputBitmap: Output bitmap segment	Bitmap port	0 - 1024	-1024 -
Threshold Minimum *	Float	1 - 1
Threshold Maximum *	Float	1 - 1
Complement Mode	String	0 - 1	ON | OFF Default: OFF
Bitmap Layer Name	String	0 - 1
Bitmap Layer Description	String	0 - 1

* Required parameter

Parameter descriptions

Input: Input raster channel

The image channel or channels to be thresholded.

For each channel specified, the entire image area will be processed.

OutputBitmap: Output bitmap segment

The bitmap segment or segments to receive the results of thresholding.

If no value is specified for this parameter, an output bitmap of segment type 101 will be created.

Threshold Minimum

The minimum threshold value.

When the value of the COMP (Complement Mode) parameter is OFF (default), gray values within the range specified by the Threshold Minimum and Threshold Maximum parameters (including the range values themselves) are turned on for the bitmap (assigned a bit-value of 1). When the same value is entered for the threshold minimum and maximum, all pixels with that value will be turned on for the bitmap.

When the value of the COMP (Complement Mode) parameter is ON, all values within the range will be turned off (assigned a bit-value of 0) in the output bitmap. For more information, see Details.

Threshold Maximum

The maximum threshold value.

When the value of the COMP (Complement Mode) parameter is OFF (default), gray values within the range specified by the Threshold Minimum and Threshold Maximum parameters (including the range values themselves) are turned on for the bitmap (assigned a bit-value of 1). When the same value is entered for the threshold minimum and maximum, all pixels with that value will be turned on for the bitmap.

When the value of the COMP (Complement Mode) parameter is ON, all values within the range will be turned off (assigned a bit-value of 0) in the output bitmap. For more information, see Details.

Complement Mode

Specifies whether to use the complement or negative bitmap mode for thresholding.

Bitmap Layer Name

The name (up to eight characters) of the output bitmap segments.

If no value is specified for this parameter, a default name of THR is used.

Bitmap Layer Description

A description of up to 64 characters of the contents or origins of the output data.

Details

THR creates threshold bitmap segments from a set of image channels. Each input channel is processed independently and results in one corresponding output bitmap. When the value of the COMP (Complement Mode) parameter is OFF, for each input pixel value between the minimum and maximum threshold gray-level values inclusively (TVAL), corresponding bits are turned on in the output bitmaps (assigned a bit-value of 1). For each input pixel value outside this range, the corresponding bits are turned off. When the maximum threshold value is not specified, every pixel above the minimum threshold value will be turned on.

When the value of the COMP (Complement Mode) parameter is ON, the complement of the resulting bitmap is stored. That is, all bits inside the threshold range are turned off (assigned a bit-value of 0), and bits outside the range are turned on (assigned a bit-value of 1).

If no output bitmap segment is specified, the function creates a new set of bitmaps, writing the segment numbers to the user and updating the LASC parameter with the segment number of the last segment created. A segment name (DBSN) of from one to eight characters, and a segment descriptor (DBSD) of from one to 64 characters, can be specified for the newly created bitmap segments; the default segment name is THR.

When an existing bitmap segment is specified, it will be overwritten by the results of THR.

Note that NoData pixels are excluded from consideration with one exception. When THR is run with threshold minimum and maximum are both specified as the NoData number, then pixels equal to that value will be turned on in the output bitmap. For example: COMP=OFF, TVAL=0,0 and NoData=0 would produce a bitmap of the NoData areas in the input raster.