=pod

=head1 NAME



B<FunImageGet - get an image or image section>



=head1 SYNOPSIS





  #include <funtools.h>

  void *FunImageGet(Fun fun, void *buf, char *plist)





=head1 DESCRIPTION




The B<FunImageGet()> routine returns an binned image array of the
specified section of a Funtools data file.  If the input data are
already of type image, the array is generated by extracting the
specified image section and then binning it according to the specified
bin factor.  If the input data are contained in a binary table or raw
event file, the rows are binned on the columns specified by the
B<bincols=> keyword (using appropriate default columns as
necessary), after which the image section and bin factors are
applied. In both cases, the data is automatically converted from FITS
to native format, if necessary.

The first argument is the Funtools handle returned by 
FunOpen().  The second B<buf>
argument is a pointer to a data buffer to fill. If NULL is specified,
FunImageGet will allocate a buffer of the appropriate size. Generally
speaking, you always want Funtools to allocate the buffer because
the image dimensions will be determined by
Funtools image sectioning
on the command line.

The third B<plist> (i.e., parameter list) argument is a string
containing one or more comma-delimited B<keyword=value>
parameters.  It can be used to specify the return data type using the
B<bitpix=> keyword.  If no such keyword is specified in the plist
string, the data type of the returned image is the same as the data type
of the original input file, or is of type int for FITS binary tables.


If the B<bitpix=> keyword is supplied in the plist string, the data
type of the returned image will be one of the supported FITS image
data types:


=over 4




=item *

8 unsigned char


=item *

16 short


=item *

32 int


=item *

-32 float


=item *

-64 double


=back


For example:

  void *buf;
  /* extract data section into an image buffer */
  if( !(buf = FunImageGet(fun, NULL, NULL)) )
    gerror(stderr, "could not FunImageGet: %s\n", iname);

will allocate buf and retrieve the image in the file data format. In
this case, you will have to determine the data type (using the
FUN_SECT_BITPIX value in the 
FunInfoGet()
routine)
and then use a switch statement to process each data type:

  int bitpix;
  void *buf;
  unsigned char *cbuf;
  short *sbuf;
  int *ibuf;
  ...
  buf = FunImageGet(fun, NULL, NULL);
  FunInfoGet(fun, FUN_SECT_BITPIX,  &bitpix, 0);
  /* set appropriate data type buffer to point to image buffer */
  switch(bitpix){
  case 8:
    cbuf = (unsigned char *)buf; break;
  case 16:
    sbuf = (short *)buf; break;
  case 32:
    ibuf = (int *)buf; break;
 ...

See the 
imblank example code
for more details on how to process an image when the data type is not
specified beforehand.


It often is easier to specify the data type directly:

  double *buf;
  /* extract data section into a double image buffer */
  if( !(buf = FunImageGet(fun, NULL, "bitpix=-64")) )
    gerror(stderr, "could not FunImageGet: %s\n", iname);

will extract the image while converting to type double.


On success, a pointer to the image buffer is returned. (This will be
the same as the second argument, if NULL is not passed to the latter.)
On error, NULL is returned.


In summary, to retrieve image or row data into a binned image, you simply
call FunOpen() followed by 
FunImageGet().  Generally, you
then will want to call
FunInfoGet()
to retrieve the
axis dimensions (and data type) of the section you are processing
(so as to take account of sectioning and blocking of the original data):

  double *buf;
  int i, j;
  int dim1, dim2;
  ... other declarations, etc.

  /* open the input FITS file */
  if( !(fun = FunOpen(argv[1], "rc", NULL)) )
    gerror(stderr, "could not FunOpen input file: %s\n", argv[1]);

  /* extract and bin the data section into a double float image buffer */
  if( !(buf = FunImageGet(fun, NULL, "bitpix=-64")) )
    gerror(stderr, "could not FunImageGet: %s\n", argv[1]);

  /* get dimension information from funtools structure */
  FunInfoGet(fun, FUN_SECT_DIM1, &dim1, FUN_SECT_DIM2, &dim2, 0);

  /* loop through pixels and reset values below limit to value */
  for(i=0; i<dim1*dim2; i++){
    if( buf[i] <= blimit ) buf[i] = bvalue;
  }



Another useful plist string value is "mask=all", which returns an
image populated with regions id values. Image pixels within a region
will contain the associated region id (region values start at 1), and
otherwise will contain a 0 value. Thus, the returned image is a
region mask which can be used to process the image data (which
presumably is retrieved by a separate call to FunImageGet) pixel by
pixel.


If a FITS binary table or a non-FITS raw event file is being binned
into an image, it is necessary to specify the two columns that will be
used in the 2D binning.  This usually is done on the command line
using the B<bincols=(x,y)> keyword:

  funcnts "foo.ev[EVENTS,bincols=(detx,dety)]"



The full form of the B<bincols=> specifier is:

  bincols=([xname[:tlmin[:tlmax:[binsiz]]]],[yname[:tlmin[:tlmax[:binsiz]]]])

where the tlmin, tlmax, and binsiz specifiers determine the image binning
dimensions:

  dim = (tlmax - tlmin)/binsiz     (floating point data)
  dim = (tlmax - tlmin)/binsiz + 1 (integer data)

These tlmin, tlmax, and binsiz specifiers can be omitted if TLMIN,
TLMAX, and TDBIN header parameters (respectively) are present in the
FITS binary table header for the column in question.  Note that if
only one parameter is specified, it is assumed to be tlmax, and tlmin
defaults to 1. If two parameters are specified, they are assumed to be
tlmin and tlmax.


If B<bincols> is not specified on the command line, Funtools tries
to use appropriate defaults: it looks for the environment variable
FITS_BINCOLS (or FITS_BINKEY). Then it looks for the Chandra
parameters CPREF (or PREFX) in the FITS binary table header. Failing
this, it looks for columns named "X" and "Y" and if these are not
found, it looks for columns containing the characters "X" and "Y".

See Binning FITS Binary Tables and
Non-FITS Event Files for more information.




=head1 SEE ALSO



See funtools(n) for a list of Funtools help pages


=cut