pngpack.f

Go to the documentation of this file.

 
 
 
      subroutine pngpack(fld,width,height,idrstmpl,cpack,lcpack)
 
      integer,intent(in) :: width,height
      real,intent(in) :: fld(width*height)
      character(len=1),intent(out) :: cpack(*)
      integer,intent(inout) :: idrstmpl(*)
      integer,intent(out) :: lcpack
 
      real(4) :: ref,rmin4
      real(8) :: rmin,rmax
      integer(4) :: iref
      integer :: ifld(width*height), nbits
      integer,parameter :: zero=0
      integer :: enc_png
      character(len=1),allocatable :: ctemp(:)
      
      ndpts=width*height
      bscale=2.0**real(-idrstmpl(2))
      dscale=10.0**real(idrstmpl(3))
!
!  Find max and min values in the data
!
      if(ndpts>0) then
         rmax=fld(1)
         rmin=fld(1)
      else
         rmax=1.0
         rmin=1.0
      endif
      do j=2,ndpts
        if (fld(j).gt.rmax) rmax=fld(j)
        if (fld(j).lt.rmin) rmin=fld(j)
      enddo
      maxdif=nint((rmax-rmin)*dscale*bscale)
!
!  If max and min values are not equal, pack up field.
!  If they are equal, we have a constant field, and the reference
!  value (rmin) is the value for each point in the field and
!  set nbits to 0.
!
      if (rmin.ne.rmax .AND. maxdif.ne.0) then
        !
        !  Determine which algorithm to use based on user-supplied 
        !  binary scale factor and number of bits.
        !
        if (idrstmpl(2).eq.0) then
           !
           !  No binary scaling and calculate minimum number of 
           !  bits in which the data will fit.
           !
           imin=nint(rmin*dscale)
           imax=nint(rmax*dscale)
           maxdif=imax-imin
           temp=alog(real(maxdif+1))/alog(2.0)
           nbits=ceiling(temp)
           rmin=real(imin)
           !   scale data
           do j=1,ndpts
             ifld(j)=nint(fld(j)*dscale)-imin
           enddo
        else
           !
           !  Use binary scaling factor and calculate minimum number of 
           !  bits in which the data will fit.
           !
           rmin=rmin*dscale
           rmax=rmax*dscale
           maxdif=nint((rmax-rmin)*bscale)
           temp=alog(real(maxdif+1))/alog(2.0)
           nbits=ceiling(temp)
           !   scale data
           do j=1,ndpts
             ifld(j)=max(0,nint(((fld(j)*dscale)-rmin)*bscale))
           enddo
        endif
        !
        !  Pack data into full octets, then do PNG encode.
        !  and calculate the length of the packed data in bytes
        !
        if (nbits.le.8) then
            nbits=8
        elseif (nbits.le.16) then
            nbits=16
        elseif (nbits.le.24) then
            nbits=24
        else 
            nbits=32
        endif
        nbytes=(nbits/8)*ndpts
        allocate(ctemp(nbytes))
        call g2_sbytesc(ctemp,ifld,0,nbits,0,ndpts)
        !
        !  Encode data into PNG Format.
        !
        lcpack=enc_png(ctemp,width,height,nbits,cpack)
        if (lcpack.le.0) then
           print *,'pngpack: ERROR Encoding PNG = ',lcpack
        endif
        deallocate(ctemp)
 
      else
        nbits=0
        lcpack=0
      endif
 
!
!  Fill in ref value and number of bits in Template 5.0
!
      rmin4=rmin
      call mkieee(rmin4,ref,1)   ! ensure reference value is IEEE format
!      call g2_gbytec(ref,idrstmpl(1),0,32)
      iref=transfer(ref,iref)
      idrstmpl(1)=iref
      idrstmpl(4)=nbits
      idrstmpl(5)=0         ! original data were reals
 
      return
      end