Pamarith User Manual(0)				       Pamarith User Manual(0)



NAME
       pamarith - perform arithmetic on two Netpbm images


SYNOPSIS
       pamarith	 -add | -subtract | -multiply | -divide | -difference | -mini-
       mum | -maximum | -mean | -compare | -and | -or | -nand | -nor | -xor  |
       -shiftleft | -shiftright pamfile1 pamfile2

       All  options  can  be abbreviated to their shortest unique prefix.  You
       may use two hyphens instead of one.  You may separate  an  option  name
       and its value with white space instead of an equals sign.


DESCRIPTION
       This program is part of Netpbm(1).

       pamarith	 reads two PBM, PGM, PPM, or PAM images as input.  It performs
       the specified binary arithmetic operation on their  sample  values  and
       produces	 an  output  of	 a format which is the more general of the two
       input formats.  The two input images must be  of	 the  same  width  and
       height.	 The  arithmetic  is  performed	 on  each  pair of identically
       located tuples to generate the identically located tuple of the output.

       For the purpose of the calculation, it assumes any  PBM,	 PGM,  or  PPM
       input  image  is	 the equivalent PAM image of tuple type BLACKANDWHITE,
       GRAYSCALE, or RGB, respectively, and if it produces a PBM, PGM, or  PPM
       output, produces the equivalent of the PAM image which is the result of
       the calculation.

       The first pamfile argument identifies the 'left'	 argument  image;  the
       second pamfile argument identifies the 'right' one.

       If  the	output is PAM, the tuple type is the same as the tuple type of
       the left input image.

       pamarith performs the arithmetic on each pair  of  identically  located
       tuples in the two input images.

       The  arithmetic operation is in all cases fundamentally a function from
       two integers to an integer.  The operation is performed on  two	tuples
       as  follows.   The two input images must have the same depth, or one of
       them must have depth one.  pamarith fails if one of these  is  not  the
       case.

       If they have the same depth, pamarith simply carries out the arithmetic
       one sample at a time.  I.e. if at a particular position the left	 input
       image  contains the tuple (s1,s2,...,sN) and the right input image con-
       tains the tuple (t1,t2,...tN), and the function is f, then  the	output
       image contains the tuple (f(s1,t1),f(s2,t2),...,f(sN,tN)).

       If  one	of the images has depth 1, the arithmetic is performed between
       the one sample in that image and each of	 the  samples  in  the	other.
       I.e.  if	 at  a	particular  position the left input image contains the
       tuple (s) and the right input image contains the	 tuple	(t1,t2,...tN),
       and  the	 function  is  f,  then	 the  output  image contains the tuple
       (f(s,t1),f(s,t2),...,f(s,tN)).


   Maxval
       The meanings of the samples with respect to the maxval varies according
       to the function you select.

       In  PAM	images in general, the most usual meaning of a sample (the one
       that applies when a PAM image represents a visual image),  is  that  it
       represents  a fraction of some maximum.	The maxval of the image corre-
       sponds to some maximum value (in the case of a visual image, it	corre-
       sponds  to 'full intensity.'), and a sample value divided by the maxval
       gives the fraction.

       For pamarith, this interpretation applies  to  the  regular  arithmetic
       functions:  -add, -subtract, -multiply, -divide, -difference, -minimum,
       -maximum, -mean, and -compare.  For those,  you	should	think  of  the
       arguments  and  result  as numbers in the range [0,1).  For example, if
       the maxval of the left argument image is 100  and  the  maxval  of  the
       right  argument image is 200 and the maxval of the output image is 200,
       and the left sample value in an -add calculation is 50  and  the	 right
       sample  is 60, the actual calculation is 50/100 + 60/200 = 160/200, and
       the output sample value is 160.

       For these functions, pamarith makes the output image's maxval the maxi-
       mum of the two input maxvals, except with -compare, where pamarith uses
       an output maxval of 2.  (Before Netpbm 10.14 (February 2003), there was
       no  exception  for  -compare; in 10.14, the exception was just that the
       maxval was at least 2, and sometime between 10.18  and  10.26  (January
       2005), it changed to being exactly 2).

       If the result of a calculation falls outside the range [0, 1), pamarith
       clips it -- i.e.	 considers it to be zero or 1-.

       In many cases, where both your input maxvals are the same, you can just
       think  of  the  operation  as  taking  place  between the sample values
       directly, with no consideration of the maxval except for the  clipping.
       E.g.  an	 -add  of sample value 5 to sample value 8 yields sample value
       13.

       But with -multiply, this doesn't work.  Say your two input images  have
       maxval 255, which means the output image also has maxval 255.  Consider
       a location in the image where the input sample values  are  5  and  10.
       You  might  think the multiplicative product of those would yield 50 in
       the output.  But pamarith carries out the arithmetic on	the  fractions
       5/255  and  10/255.   It multiplies those together and then rescales to
       the output maxval, giving a sample value in the output  PAM  of	50/255
       rounded to the nearest integer: 0.

       With  the bit string operations, the maxval has a whole different mean-
       ing.  The operations in question are: -and, -or, -nand, -nor, -xor, and
       -shiftleft, -shiftright.

       With  these,  each sample value in one or both input images, and in the
       output image, represents a bit string, not a number.  The maxval	 tells
       how  wide the bit string is.  The maxval must be a full binary count (a
       power of two minus one, such as 0xff) and the number of ones in	it  is
       the  width  of  the  bit	 string.  For the dyadic bit string operations
       (that's everything but the shift functions), the maxvals of  the	 input
       images  must  be	 the  same and pamarith makes the maxval of the output
       image the same.

       For the bit shift operations, the output maxval is the same as the left
       input  maxval.  The right input image (which contains the shift counts)
       can have any maxval and the maxval is irrelevant to the	interpretation
       of  the samples.	 The sample value is the actual shift count.  But it's
       still required that no sample value exceed the maxval.


   The Operations
       Most of the operations are obvious from the option name.	 The following
       paragraphs cover those that aren't.

       -subtract  subtracts  a	value in the right input image from a value in
       the left input image.

       -difference calculates the absolute value of the difference.

       -multiply does an ordinary arithmetic multiplication, but tends to pro-
       duce  nonobvious	 results because of the way pamarith interprets sample
       values.	See Maxval <#maxval> .

       -divide divides a value in the left input image by  the	value  in  the
       left  input  image.  But like -multiply, it tends to produce nonobvious
       results.	 Note that pamarith clipping behavior makes this of little use
       when  the  left	argument (dividend) is greater than the right argument
       (divisor) -- the result in that case is	always	the  maxval.   If  the
       divisor	is 0, the result is the maxval.	 This option was new in Netpbm
       10.30 (October 2005).

       -compare produces the value 0 when the value in the left input image is
       less  than  the	value  in the right input image, 1 when the values are
       equal, and 2 when the left is greater than the right.

       If the maxvals of the input images  are	not  identical,	 pamarith  may
       claim two values are not equal when in fact they are, due to the preci-
       sion with which it does the arithmetic.	However, it will never	say  A
       is greater than B if A is less than B.

       -compare was new in Netpbm 10.13 (December 2002).

       -and,  -nand,  -or, -nor, and -xor consider the input and output images
       to contain bit strings; they compute bitwise  logic  operations.	  Note
       that if the maxval is 1, you can also look at these as logic operations
       on boolean input values.	 See section Maxval <#maxval>  for the special
       meaning of maxval with respect to bit string operations such as these.

       -shiftleft  and	-shiftright  consider  the left input image and output
       image to contain bit strings.  They compute a bit shift operation, with
       bits  falling  off  the	left  or  right end and zeroes shifting in, as
       opposed to bits off one end to the other.  The right input image sample
       value is the number of bit positions to shift.

       Note  that  the	maxval (see Maxval <#maxval> ) determines the width of
       the frame within which you are shifting.


   Notes
       If you want to apply a unary function, e.g. "halve", to a single image,
       use pamfunc.


SEE ALSO
       pamfunc(1),  pamsummcol(1),  pamsumm(1),	 pnminvert(1), ppmbrighten(1),
       ppmdim(1), pnmconvol(1), pamdepth(1), pnmpsnr(1), pnm(1), pam(1)



HISTORY
       pamarith replaced pnmarith in Netpbm 10.3 (June 2002).

       In Netpbm 10.3 through 10.8, though, pamarith was not backward compati-
       ble  because  it	 required the input images to be of the same depth, so
       you could not multiply a PBM by a PPM as is  often  done	 for  masking.
       (It  was	 not  intended at the time that pnmarith would be removed from
       Netpbm -- the plan was just to rewrite  it  to  use  pamarith;  it  was
       removed by mistake).

       But  starting  with  Netpbm  10.9 (September 2002), pamarith allows the
       images to have different depths as long as one of them has depth 1, and
       that made it backward compatible with pnmarith.

       The original pnmarith did not have the -mean option.

       The -compare option was added in Netpbm 10.13 (December 2002).

       The bit string operations were added in Netpbm 10.27 (March 2005).

       The -divide option was added in Netpbm 10.30 (October 2005).



netpbm documentation		 08 April 2007	       Pamarith User Manual(0)