THRESH - Edits an NDF to replace values between or outside given limits with specified constant values

Description:

This application creates an output NDF  by copying values from an input NDF, replacing all values within given data ranges by a user-specified constant or by the bad value. Upper and lower thresholds are supplied using Parameters THRLO and THRHI.

If THRLO is less than or equal to THRHI, values between and including the two thresholds are copied from the input to output array. Any values in the input array greater than the upper threshold will be set to the value of Parameter NEWHI, and anything less than the lower threshold will be set to the value of Parameter NEWLO, in the output data array. Thus the output NDF is constrained to lie between the two bounds.

If THRLO is greater than THRHI, values greater than or equal to THRLO are copied from the input to output array, together with values less than or equal to THRHI. Any values between THRLO and THRHI will be set to the value of Parameter NEWLO in the output NDF.

Each replacement value may be the bad-pixel  value for masking.

Usage:

thresh in out thrlo thrhi newlo newhi [comp]

Parameters:

COMP = LITERAL (Read)

The components whose values are to be constrained between thresholds. The options are limited to the arrays within the supplied NDF. In general the value may be "Data", "Quality", "Error", or "Variance". If "Quality" is specified, then the quality values are treated as numerical values in the range 0 to 255. ["Data"]

IN = NDF (Read)

Input NDF structure containing the array to have thresholds applied.

NEWHI = LITERAL (Read)

This gives the value to which all input array-element values greater than the upper threshold are set. If this is set to "Bad", the bad value is substituted. Numerical values of NEWHI must lie in within the minimum and maximum values of the data type of the array being processed. The suggested default is the upper threshold. This parameter is ignored if THRLO is greater than THRHI.

NEWLO = LITERAL (Read)

This gives the value to which all input array-element values less than the lower threshold are set. If this is set to "Bad", the bad value is substituted. Numerical values of NEWLO must lie in within the minimum and maximum values of the data type of the array being processed. The suggested default is the lower threshold.

OUT = NDF (Write)

Output NDF structure containing the thresholded version of the array.

THRHI = _DOUBLE (Read)

The upper threshold value within the input array. It must lie in within the minimum and maximum values of the data type of the array being processed. The suggested default is the current value.

THRLO = _DOUBLE (Read)

The lower threshold value within the input array. It must lie within the minimum and maximum values of the data type of the array being processed. The suggested default is the current value.

TITLE = LITERAL (Read)

Title for the output NDF structure. A null value (!) propagates the title from the input NDF to the output NDF. [!]

Results Parameters:

NUMHI = _INTEGER (Write)

The number of pixels whose values were thresholded as being greater than the THRHI threshold.

NUMLO = _INTEGER (Write)

The number of pixels whose values were thresholded as being less than the THRLO threshold.

NUMRANGE = _INTEGER (Write)

The number of pixels whose values were thresholded as being between the THRLO and THRHI thresholds, if THRLO is greater than THRHI.

NUMSAME = _INTEGER (Write)

The number of unchanged pixels.

Examples:

thresh zzcam zzcam2 100 500 0 0

This copies the data array in the NDF called zzcam to the NDF called zzcam2. Any data value less than 100 or greater than 500 in zzcam is set to 0 in zzcam2.

thresh zzcam zzcam2 500 100 0

This copies the data array in the NDF called zzcam to the NDF called zzcam2. Any data value less than 500 and greater than 100 in zzcam is set to 0 in zzcam2.

thresh zzcam zzcam2 100 500 0 0 comp=Variance

As above except that the data array is copied unchanged and the thresholds apply to the variance array.

thresh n253 n253cl thrlo=-0.5 thrhi=10.1 $\backslash$

This copies the data array in the NDF called n253 to the NDF called n253cl. Any data value less than $-$0.5 in n253 is set to $-$0.5 in n253cl, and any value greater than 10.1 in n253 becomes 10.1 in n253cl.

thresh pavo pavosky -0.02 0.02 bad bad

All data values outside the range $-$0.02 to 0.02 in the NDF called pavo become bad in the NDF called pavosky. All values within this range are copied from pavo to pavosky.

Related Applications

KAPPA: HISTEQ, MATHS; FIGARO: CLIP, IDIFF, RESCALE.

Implementation Status:

• This routine correctly processes the AXIS, DATA, QUALITY, VARIANCE, LABEL, TITLE, UNITS, WCS, and HISTORY  components of an NDF data structure and propagates all extensions.

• Processing of bad pixels and automatic quality masking are supported.

• All non-complex numeric data types can be handled.

• Any number of NDF dimensions is supported.