User's Guide

GAUSTRAN

Applies a Gaussian transfer function to an image

Function:

Applies a Gauss transfer function to an input image to form an output image.

Parameters:

IN
Input image. Specifies the input image to which the Gauss transfer function will be applied. The data type of IN may be BYTE, INTEGER*2, INTEGER*4, or REAL*4 and it may contain up to 50 bands.

OUT
Output image. Specifies the output image. It will consist of one band for each input image band. Each output band is the result of calculations applied to its corresponding input band. The data type of OUT is REAL*4.

SCALFACT(1.0)
Scale factor. An SCALFACT value should be specified for each input band; if a value is omitted for a band, SCALFACT will default to 1.0 for that band. The values must be positive (see User's Notes for more details).

EXPSF(1.0)
Exponent scale factor. A EXPSF value should be specified for each input band; if a value is omitted for a band, EXPSF will default to 1.0 for that band. The values must be positive (see User's Notes for more details).

OFFSET(0.0)
Offset value. One value of OFFSET for each input band should be specified. If OFFSET is not specified for an input band, it will default to 0.0 for that band only (see the User's Notes for more details).

Examples:

LAS> gaustran in="myimg.in(:1-3)" out=img.dat
This generates the Gauss transfer function using the default values for the parameters SCALFACT, EXPSF, and OFFSET and applies it to the three bands specified for the input image MYIMG.IN.
LAS> gaustran in=four.in out=mag.out scalfact=2.0 expsf=2.0 offset=0.5
This generates the Gauss transfer function using the specified values for SCALFACT, EXPSF, and OFFSET and applies it to the input image FOUR.IN.

Description/Algorithm:

GAUSTRAN processes each band sequentially on a pixel-by-pixel basis. The user may enter up to 50 values for SCALFACT, EXPSF, and OFFSET, but there must be an equal number of image bands to process them. A warning will be generated if the user enters too few values for SCALFACT, EXPSF, or OFFSET.
The output image is produced as follows:
                       -EXPSF*(IN(x,y)-OFFSET)**2
  OUT(x,y)=SCALFACT * e

Nonfatal Error Messages:

[gaustran-scalfact] Number of SCALFACT values < number of bands - using default
The user has supplied an image which has more bands than there are SCALFACT values. A warning is issued and the processing continues with the default values for the remaining SCALFACTs.
[gaustran-expsf] Number of EXPSF values < number of bands - using default
The user has supplied an image which has more bands than there are EXPSF values. A warning is issued and the processing continues with the default values for the remaining EXPSFs.
[gaustran-offset] Number of offset values < number of bands - using default
The user has supplied an image which has more bands than there are OFFSET values. A warning is issued and the processing continues with the default values for the remaining OFFSETS.

Fatal Error Messages:

None.

User's Notes:

The equation used in GAUSTRAN resembles the function for a Gaussian (normal) distribution, when


                           1 
            SCALFACT =   ------ 
                            2
                           s  


                         1 
            EXPSF  =   ------  
                         2
                        s

     s      = the standard deviation of the input
              image and
     OFFSET = the mean of the input image
                                
    Then the equation becomes
                                        
                     1                           2    2   
     OUT(x,y) =   -----  exp ( -(IN(x,y)-OFFSET) / 2s  ) 
                      2
                     s

This equation defines the distribution function of a normal distribution.

If the user does not enter enough values for SCALFACT, EXPSF, or OFFSET, GAUSTRAN will use the default values of 1.0, 1.0, and 0.0 (respectively) for these parameters. If the user enters more values than input image bands, the extra values are ignored.