Basic Information on immask

Task: immask
Purpose: mask an image dataset
Categories: image analysis

      PROGRAM immask
 
    IMMASK is a MIRIAD task which allows you to mask an image
    dataset, or find out the number of masked pixels in an image.
 
    Masking is directly done to the ``mask'' item of an image dataset, i.e.
    the actual image data are not modified, only the mask.
    A pixel with a TRUE mask value is considered a good pixel.
 
    To set all pixels in an image to FALSE:
        immask in=ngc_289_6cm flag=false logic=and
 
    To mask out the pixels in a region:
        immask in=ngc_289_20cm region=@cgcurs.region flag=false logic=and
 
    To undo all masking, delete the mask item from the header:
        delhd in=ngc_289_6cm/mask
 
    To mask all the pixels EXCEPT a chosen region (eg you want to blank out
    the nasty-looking edges of a CCD image)
        immask in=myimage flag=good region=@good.region logic=not
 
    To change the masking, you must specify a value for the LOGIC keyword.
    Otherwise IMMASK merely reports the current numbers of masked and
    unmasked pixels.
 
    See also MATHS for other ways to set the image mask, but note
    that un-masking a pixel may then expose a value that is incorrect
    or unexpected, e.g. maths will have written 0s for pixels that were
    masked in the process.
 

Key: in
    The name of the input image dataset. No default.
 

Key: region
    Regions which will be masked with the ``flag'' value (see below).
    Full region descriptions are supported.
    Note that missing image planes will be automatically masked
    to the opposite value set by the ``flag'' keyword below.
    Default: whole image.
 

Key: logic
    The logic of the masking operation. It can have a value of ``AND'',
    `OR'' or ``NOT'' which determines how the selected region(s) from the
    region= keyword are masked with the existing mask item in the image:
        OR:     region .OR.   mask
        AND:    region .AND.  mask
        EQV:    region .EQV.  mask
        XOR:    region .XOR.  mask
        NOT:    if (region) .NOT.mask
    If no value provided, the program will simply report on the
    total number of pixels already flagged good and bad.
    Caution: although XOR is not a valid fortran expression, the
    EQV and NEQV boolean operators come close. OR and XOR belong
    together: OR=inclusive OR, XOR=exclusive OR.
    No default.
 

Key: flag
    The value of the mask inside the selected regions. Can be ``true''
    or ``false''. Outside selected region it will be its opposite.
    A ``true'' value is considerd a good pixel.
    Default: true.
 

Key: history
    Specifies whether the history should be updated. This should
    normally never be set to false, though some scripts prefer
    to do this manually via ADDHIS, and set this parameter to FALSE.
    In reporting mode (no ``logic'' operation supplied) the history
    is not updated.
    Default: TRUE
 

Key: options
    Valid options:
       datamin      flag all values with `flag' when they equal the
                    value of the 'datamin' keyword in the image header.
    Default: none.