PCOMB(1)						      General Commands Manual							  PCOMB(1)

NAME
       pcomb - combine RADIANCE pictures

SYNOPSIS
       pcomb [ -h ][ -w ][ -x xres ][ -y yres ][ -f file ][ -e expr ] [ [ -o ][ -s factor ][ -c r g b ] input ..  ]

DESCRIPTION
       Pcomb combines equal-sized RADIANCE pictures and sends the result to the standard output.  By default, the result is just a linear combina-
       tion of the input pictures multiplied by -s and -c coefficients, but an arbitrary mapping can be assigned with the -e and -f options.  Neg-
       ative coefficients and functions are allowed, and pcomb will produce color values of zero where they would be negative.

       The variables ro, go and bo specify the red, green and blue output values, respectively.  Alternatively, the single variable lo can be used
       to specify a brightness value for black and white output.  The predefined functions ri(n), gi(n) and bi(n) give the  red,  green  and  blue
       input  values  for picture n.  To access a pixel that is nearby the current one, these functions also accept optional x and y offsets.  For
       example, ri(3,-2,1) would return the red component of the pixel from picture 3 that is left 2 and up 1 from the current position.  Although
       x  offsets  may	be  as large as width of the picture, y offsets are limited to a small window (+/- 32 pixels) due to efficiency considera-
       tions.  However, it is not usually necessary to worry about this problem -- if the requested offset is not available, the next  best  pixel
       is returned instead.

       For  additional	convenience, the function li(n) is defined as the input brightness for picture n.  This function also accepts x and y off-
       sets.

       The constant nfiles gives the number of input files present, and WE gives the white efficacy (lumens/brightness) for  pixel  values,  which
       may  be	used  with the -o option or the le(n) values to convert to absolute photometric units (see below).  The variables x and y give the
       current output pixel location for use in spatially dependent functions, the constants xmax and ymax give the input resolution, and the con-
       stants  xres  and yres give the output resolution (usually the same, but see below).  The constant functions re(n), ge(n), be(n), and le(n)
       give the exposure values for picture n, and pa(n) gives the corresponding pixel aspect ratio.   Finally,  for  pictures	with  stored  view
       parameters,  the functions Ox(n), Oy(n) and Oz(n) return the ray origin in world coordinates for the current pixel in picture n, and Dx(n),
       Dy(n) and Dz(n) return the normalized ray direction.  In addition, the function T(n) returns the distance from the origin to the aft  clip-
       ping  plane  (or  zero  if there is no aft plane), and the function S(n) returns the solid angle of the current pixel in steradians (always
       zero for parallel views).  If the current pixel is outside the view region, T(n) will return a negative value, and S(n) will return zero.

       The -h option may be used to reduce the information header size, which can grow disproportionately after  multiple  runs  of  pcomb  and/or
       pcompos(1).   The  -w  option  can  be used to suppress warning messages about invalid calculations.  The -o option indicates that original
       pixel values are to be used for the next picture, undoing any previous exposure changes or color correction.

       The -x and -y options can be used to specify the desired output resolution, xres and yres, and can be expressions involving other constants
       such  as  xmax  and ymax.  The constants xres and yres may also be specified in a file or expression.  The default output resolution is the
       same as the input resolution.

       The -x and -y options must be present if there are no input files, when the definitions of ro, go and bo will be used to compute each  out-
       put  pixel.   This  is useful for producing simple test pictures for various purposes.  (Theoretically, one could write a complete renderer
       using just the functional language...)

       The standard input can be specified with a hyphen ('-').  A command that produces a RADIANCE picture can be given in place  of  a  file	by
       preceeding it with an exclamation point ('!').

EXAMPLES
       To produce a picture showing the difference between pic1 and pic2:

	 pcomb -e 'ro=ri(1)-ri(2);go=gi(1)-gi(2);bo=bi(1)-bi(2)' pic1 pic2 > diff

       Or, more efficiently:

	 pcomb pic1 -s -1 pic2 > diff

       To precompute the gamma correction for a picture:

	 pcomb -e 'ro=ri(1)^.4;go=gi(1)^.4;bo=bi(1)^.4' inp.hdr > gam.hdr

       To perform some special filtering:

	 pcomb -f myfilt.cal -x xmax/2 -y ymax/2 input.hdr > filtered.hdr

       To make a picture of a dot:

	 pcomb -x 100 -y 100 -e 'ro=b;go=b;bo=b;b=if((x-50)^2+(y-50)^2-25^2,0,1)' > dot

AUTHOR
       Greg Ward

SEE ALSO
       getinfo(1), icalc(1), pcompos(1), pfilt(1), rpict(1)

RADIANCE							      8/31/96								  PCOMB(1)