subroutine CONVOL(ITYPE,BUF1,BUF2,BUF3,alpha,beta,BUF4,INIT)
C
C	EMULATES Comtal convolver algorithm
C	called by using several switches and args -- all goes to same 
C	computaional code but each has own method of calculating
C	the KERNEL coeffs.
C
C	type = 0 for unsharp masking algorithm
C		1 for isotropic alpha , beta algorithm
C			use /CO:a   or   /CO:a:b to envoke
C	type = 2 explicit kernel load /KE:a:b:c:d:e:f:g:h:i
C	type = 3 despiking filter use /DS:percent
C	special case-- if any element is zero dont include in sum
C	adjust total to compesate for zeros in 3x3 kernel,ie dont
C	average in zero data its non-exsistant.
C
C
	byte BUF1(512),BUF2(512),BUF3(512),BUF4(512)
	integer alpha,beta,ZEROS
	dimension alpha(9)	!special for when all 9 kernel params
	real KERNEL(3,3)
	real K			!kernel coeffs
C
C	these funny varibles aatempt to emulate the COMTAL hardware
C	convolver parameter registers ,thats why their so weird
	data NC /0/	!common scale factor
	data NE /0/	!edge scale factor
	data S  /0./	!input switch to scale resultant
C
C
	if( INIT .ne. 0 )goto 1049
C	test initial call or not , only at initial do we build KERNEL
C
C
C	use type to determine KERNEL selection
C
	if( ITYPE .ne. 0 )goto 100
C
C
C	build KERNEL
	ICONS = alpha(1)
	if( alpha(1) .le. 0 .or. alpha(1) .gt. 512  )ICONS = 256
C	compute values for center and all edge elements for unsharp
C	masking , edges = -1 and cneter = lambda -1
C	normalize all so no division done during computataion
C
C	K = -x * (1/3) * (1/512) + (1/9)
	K = ICONS * (1./3.) * (1./512.) + (1./9.)
	K = K * ( -8.0 )
	sign = 1.
	if( K .lt. 0.0 )sign = -1.
	R2 = K		!save K*8
	K = ABS(K)
	R0 = 1.0 - R2	!compute (1-8*K)
	goto 5
C
C	skip this junk we dont need NC NE we have floating point code
C
	NC = 0
	NE = 0
4	if( R0 .lt. 1.0 )goto 5
	NC = NC +1		!bump power of 2
	R0 = R0 / 2.		!drop R0 down
	if( NC .lt. 3 ) goto 4
C
5	KERNEL(2,2) = R0	!save R0 as kernel value
	R0 = K / 8.0		!get k*8 to K for R0
	goto 9
C
C	skip this code we have flt pt dont need to scale it
C
	R1 = 0.0
	NCTMP = NC
6	if( NCTMP .eq. 0 ) goto 7
	R0 = R0 / 2.0
	NCTMP = NCTMP - 1
	goto 6
7	if( R0 .ge. 1.0 )goto 8
	if( R0 .gt. .5  )goto 8
	NE = NE + 1
	R0 = R0 * 2.0
	if ( NE .lt. 3 ) goto 7
8	continue
C
C	assign coded kernel values here
C
9	continue
	R0 = sign * R0
C	reset to proper sign
20	KERNEL(1,1) = R0
	KERNEL(1,3) = R0
	KERNEL(3,1) = R0
	KERNEL(3,3) = R0
C
	KERNEL(1,2) = R0
	KERNEL(2,1) = R0
	KERNEL(2,3) = R0
	KERNEL(3,2) = R0
C
	goto 1000
C	go apply KERNEL to 3 lines
C
C********************************************************************
100	continue
	if( ITYPE .ne. 1 )goto 200
C
C	ISOTROPIC alpha(1) -- beta filter
C
C	build KERNEL
	acons = 0.0
	if( alpha(1) .eq. 0 )goto 120
	acons = 1./alpha(1)
C
120	KERNEL(1,1) = acons
	KERNEL(1,3) = acons
	KERNEL(3,1) = acons
	KERNEL(3,3) = acons
C
	bcons = 0.0
	if( beta .eq. 0 )goto 130
	bcons = 1./beta
C
130	KERNEL(1,2) = bcons
	KERNEL(2,1) = bcons
	KERNEL(2,3) = bcons
	KERNEL(3,2) = bcons
C
	KERNEL(2,2) = 1.
	goto 1000
C	**********************************************************
C
200	continue
	if( ITYPE .ne. 2 ) goto 300
C
C
C	here user has specified /KE:a:b:c:d:e:f:g:h:i
C	all nine params explicitly, good for testing & specials
C
	do 250 j=1,3
	do 250 i=1,3
250	KERNEL(i,j) = alpha((i-1)*3+j)
C
	goto 1000
C
C
300	continue
C
C	user has requested DESPIKER -- compute avg of 8 nearest neighbors
C	and compare with the center pixel. If differ by more than n% then
C	replace center value with the average of 8 nearest neighbors .
C
	PERCNT = alpha(1) * .01
C
	do 350 j=1,3
	do 350 i=1,3
350	KERNEL(i,j) = 1.0
C
	KERNEL(2,2) = 0.0
C	set cneter to zero
	goto 1000
C
C	**************************************************************
C
C	Normalize all coeffs so all less than 1.
C
1000	continue
C
	sum = 0.
C
	do 1040 j=1,3
	do 1040 i=1,3
1040	sum = KERNEL(i,j) + sum
C	summ the weights of the coeffs
	IF( SUM .EQ. 0.0 )GOTO 1046
C
	do 1045 j=1,3
	do 1045 i=1,3
1045	KERNEL(i,j) = KERNEL(i,j) / abs(sum)
C	normalize coeffs by dividing by absolute value of sum
C
1046	INIT = 1
C	once kernel coefs set dont recompute
C
C	*************************************************************
C	now apply filter just built
C
1049	continue
	do 1100 i=1,512
C
	TMP = 0.
	ZEROS = 0	!nuber of zero data values in 3x3 input data
C
		do 1050 j=1,3
		ielem = i-2+j
		if(ielem .le. 0)ielem=1
		if(ielem .gt. 512)ielem=512
		IWORD = BUF1(IELEM)
C	GET UNSIGNED POSITIVE BYTE
		if(IWORD.eq.0)ZEROS=ZEROS+1	!inc count of null data
		TMP=TMP+ (KERNEL(1,j)) * ( IWORD .and. "377 )
		IWORD = BUF2(IELEM)
C	GET UNSIGNED POSITIVE BYTE
		if(IWORD.eq.0 .and. j.ne.2 )ZEROS=ZEROS+1	!inc
		TMP=TMP+ (KERNEL(2,j)) * ( IWORD .and. "377 )
		IWORD = BUF3(IELEM)
C	GET UNSIGNED POSITIVE BYTE
		if(IWORD.eq.0)ZEROS=ZEROS+1	!inc count of null data
		TMP=TMP+ (KERNEL(3,j)) * ( IWORD .and. "377 )
1050		continue
C
C
C
C	now store byte away
	if( TMP .gt. 255.)TMP = 255.
	if( TMP .lt. 0.)TMP = 0.
	if( ITYPE .ne. 3 )goto 1090
C
C	if user has despiking filter then compare avg of 8 nearest neighbors
C	with the center value.
	CENTER = BUF2(i) .and. "377
C	value of center element
C
	if(ZEROS .ge. 8)goto 1060	!if all are zero keep center 
	TMP = TMP * (8. / (8.-ZEROS))	!scaleup to account for null data
	if(TMP .gt. 255.)TMP=255.	!keep withina byte
C	
	if( abs(TMP-CENTER)/TMP .gt. PERCNT )goto 1090
C
1060	TMP = CENTER
C	if ratio is not out of range then store back in the original pt.
C
1090	BUF4(i) = TMP
C
1100	continue
	return
	end