Wherever a bit is set to 1 in the bad-bits mask, the corresponding bit will be extracted from the NDF’s quality array value for each pixel (the other quality bits being ignored). A pixel is then considered ‘bad’ if any of the extracted quality bits is set to 1. Effectively, the bad-bits mask therefore allows selective activation of any of the eight 1-bit masks which can be stored in the quality array.
The bit mask can be given either numerically (in decimal, binary, octal or hexadecimal format), or as a set of quality names (see SETQUAL).
TRUEvalue is given for the AND parameter, then a bit-wise ‘AND’ will first be performed with the old value of the mask. This facility allows individual bits in within the mask to be cleared (i.e. reset to zero) without affecting the current state of other bits (see the
The AND parameter is not used if a
TRUE value is given for the OR parameter.
"Z"prefix (respectively) to the appropriate string of digits. The value supplied should lie in the range 0 to 255 decimal (or 8 bits of binary).
If the AND and OR parameters are both
FALSE, then the value supplied will be used
directly as the new mask value. However, if either of these logical parameters is set
TRUE, then an appropriate bit-wise ‘AND’ or ‘OR’ operation with the old mask value
will first be performed.
It may also be specified as a comma-separated list of quality names. A quality name is a symbolic name that identifies a specific quality bit (quality names can be defined using SETQUAL, and displayed using SHOWQUAL).
The default value suggested when prompting for this value is chosen so as to leave the original mask value unchanged.
TRUEvalue is given for the OR parameter, then a bit-wise ‘OR’ will first be performed with the old value of the mask. This facility allows individual bits in within the mask to be set to 1 without affecting the current state of other bits (see the
"BACK"will be set bad. The NDF should contain information that associates each of these quality names with a specific bit in the quality array. Such information can for instance be created using the SETQUAL command.