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)
