C     ****** BACKAUTO ******
C
C     PROGRAM TO CALCULATE THE MEAN RADIAL DENSITY (BACKGROUND)
C     OF AN ELECTRON DIFFRACTION PATTERN - any size rectangular area.
C       The new version has options to carry out automatic centre
C       determination, and update of the header into the invisible IEXTRA 
C       records used by the subsequent program PICKYCOR.
C
C     VERSION   FOR VAX    MAY 1982
C     VX1.0     RH,JMB   5-Feb-1992     cosmetic comments and title line added
C     VX2.0     RH      22-Mar-1992     UNIX, automatic centring and header update
C     VX2.1     RH      11-May-1992     3 passes, and only data within 2*STNDEV
C     VX2.2     RH      21-Mar-1993     default value for NSTEP=4
C     VX2.3     RH      16-Aug-1993     change highest density from 1024 to 32000
C     VX2.4     RH      19-Nov-1994     automatic centring with pointer removal
C     VX2.5     RH       2-Dec-1994     limit instability in centre refinement
C     VX2.6     RH       3-Dec-1994     centre refine uses gradient weighting. 
C     VX2.7     RH      19-Jan-1995     debug SQRT(GXY) in GETPERP
C     VX2.8     RH       2-Mar-1995     pointer - test proportion <0.5*stndev
C     VX2.9     RH      25-Jul-1995     replaced CALL PAPER by BRKPLT(1)
C     VX2.10    RH      21-Sep-1995     annotation of plot output
C     VX2.11    RH       7-OCT-1995     test for MODE=0
C     VX2.12    RH       8-OCT-1995     move first CRTPLT inside PLOTRAST
C     VX2.13    RH      22-Apr-1996     delete all refs to PDPTIT
C     VX2.14    RH      21-Jul-1996     debug radial background -- ABS(XCOORD)
C                                       plus improved XYmax/min output format
C     VX2.15    RH       6-May-1997     remove PEN(2) and PEN(3)
C     VX2.16    RH      15-Nov-1997     estimate variance in empty radius bins
C     VX2.17    RH       3-Jan-1998     print out number of pixels per radius bin
C     VX2.18    RH      24-Feb-1998     test sqrt for zero argument at TEMP3
C     VX3.00    RH      15-Aug-2000     convert to plot2000 subroutines
C     VX3.01    TSH     13-Jun-2001     P2K_FONT needed string terminator
C     VX3.02    JMS     25-Feb-2005     IDIM, IOVERLOAD increased
C
C     Plots three possible background raster choices for PICKYCOR
C       - only if IEXTRA entries in header are set for DX1,DY1,DX2,DY2
C     Plots radial background curve
C     Plots X-average, Y-average, and perimeter Y-average (YCOR)
C
C
C       Data input cards :
C
C               0.      IREF,IPLOT      if IREF.eq.'F' no automatic centring
C                                       if IREF.eq.'T' centre is determined
C                                       if IPLOT.eq.F' no plots done.
C               1.      CX,CY           Centre coords relative to centre of film
C               2.      NPLATE          Film number used to identify outputs
C               3.      TITLE           Title for same purpose
C               4.      NPNTS           smoothing over 2*NPNTS+1 in radial curve
C               5.      IRMAX,IRMIN     max and min limits for X,Y-average plots
C               6.      IRMAXC,IRMINC   max and min limits for YCORRECTION
C
C
C       Input files required and output files produced :
C
C               IN        files of the raw data
C               OUT       data corrected for radial background and y-correction
C               FORT2     radial background to be used in PICKPROFA
C               FORT4     y-correction to be used in PICKPROFA
C               PLOTBACK  plot output data, radial curve and X and Y variations
C_______________________________________________________________________________
C  Notes:  STNDEV is raw standard deviation.
C          STND1V is smoothed standard deviation over adjacent radii.
C