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
combination 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
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
considerations. 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 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
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
constants 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
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 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)