Radiance pcomb program

PCOMB(1)                                                              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.  Negative
       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 val-
       ues, respectively.  Alternatively, the single variable lo can  be  used
       to  specify  a brightness value for black and white output.  The prede-
       fined 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 cur-
       rent 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 lim-
       ited to a small window (+/- 32 pixels)  due  to  efficiency  considera-
       tions.   However, it is not usually necessary to worry about this prob-
       lem -- 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  offsets.

       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 abso-
       lute 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 clipping 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 pcom-
       pos(1).  The -w option can be used to suppress warning  messages  about
       invalid calculations.  The -o option indicates that original pixel val-
       ues 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 resolu-
       tion, xres and yres, and can be expressions involving  other  constants
       such  as xmax and ymax.  The constants xres and yres may also be speci-
       fied 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  output
       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)