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.\" RCSid "$Id: pcomb.1,v 1.5 2004/01/01 19:31:45 greg Exp $"
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.TH PCOMB 1 8/31/96 RADIANCE
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.SH NAME
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pcomb - combine RADIANCE pictures
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.SH SYNOPSIS
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.B pcomb
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[
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.B -w
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][
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.B "\-x xres"
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][
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.B "\-y yres"
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][
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.B "\-f file"
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][
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.B "\-e expr"
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]
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[
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[
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.B -o
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][
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.B "\-s factor"
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][
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.B "\-c r g b"
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]
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.B "input .."
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]
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.SH DESCRIPTION
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.I Pcomb
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combines equal-sized RADIANCE pictures and sends the result to the
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standard output.
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By default, the result is just a linear combination of
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the input pictures multiplied by
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.I \-s
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and
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.I \-c
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coefficients,
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but an arbitrary mapping can be assigned with the
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.I \-e
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and
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.I \-f
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options.
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Negative coefficients and functions are allowed, and
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.I pcomb
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will produce color values of zero where they would be negative.
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.PP
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The variables
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.I ro,
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.I go
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and
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.I bo
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specify the red, green and blue output values, respectively.
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Alternatively, the single variable
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.I lo
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can be used to specify a brightness value for black and white output.
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The predefined functions
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.I ri(n),
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.I gi(n)
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and
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.I bi(n)
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give the red, green and blue input values for
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picture
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.I n.
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To access a pixel that is nearby the current one, these functions
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also accept optional x and y offsets.
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For example,
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.I ri(3,-2,1)
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would return the red component of the pixel from picture 3
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that is left 2 and up 1 from the current position.
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Although x offsets may be as large as width of the picture,
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y offsets are limited to a small window (+/- 32 pixels) due to efficiency
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considerations.
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However, it is not usually necessary to worry about this problem --
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if the requested offset is not available, the next best pixel is
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returned instead.
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.PP
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For additional convenience, the function
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.I li(n)
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is defined as the input brightness for picture
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.I n.
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This function also accepts x and y offsets.
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.PP
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The constant
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.I nfiles
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gives the number of input files present,
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and
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.I WE
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gives the white efficacy (lumens/brightness) for pixel values,
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which may be used with the
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.I \-o
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option or the le(n) values to convert to absolute
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photometric units (see below).
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The variables
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.I x
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and
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.I y
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give the current output pixel location for use in
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spatially dependent functions, the constants
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.I xmax
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and
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.I ymax
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give the input resolution, and the constants
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.I xres
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and
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.I yres
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give the output resolution (usually the same, but see below).
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The constant functions
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.I "re(n), ge(n), be(n),"
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and
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.I le(n)
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give the exposure values for picture
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.I n,
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and
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.I pa(n)
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gives the corresponding pixel aspect ratio.
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Finally, for pictures with stored view parameters,
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the functions
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.I "Ox(n), Oy(n)"
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and
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.I Oz(n)
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return the ray origin in world coordinates for the current pixel
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in picture
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.I n,
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and
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.I "Dx(n), Dy(n)"
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and
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.I Dz(n)
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return the normalized ray direction.
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In addition, the function
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.I T(n)
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returns the distance from the origin to the aft clipping plane
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(or zero if there is no aft plane), and the function
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.I S(n)
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returns the solid angle of the current pixel in steradians
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(always zero for parallel views).
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If the current pixel is outside the view region,
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.I T(n)
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will return a negative value, and
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.I S(n)
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will return zero.
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.PP
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The
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.I \-w
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option can be used to suppress warning messages about invalid
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calculations.
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The
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.I \-o
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option indicates that original pixel values are to be used for the next
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picture, undoing any previous exposure changes or color correction.
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.PP
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The
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.I \-x
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and
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.I \-y
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options can be used to specify the desired output resolution,
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.I xres
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and
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.I yres,
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and can be expressions involving other constants such as
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.I xmax
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and
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.I ymax.
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The constants
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.I xres
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and
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.I yres
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may also be specified in a file or expression.
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The default output resolution is the same as the input resolution.
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.PP
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The
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.I \-x
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and
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.I \-y
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options must be present if there are no input files, when
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the definitions of
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.I ro,
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.I go
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and
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.I bo
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will be used to compute each output pixel.
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This is useful for producing simple test pictures for various
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purposes.
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(Theoretically, one could write a complete renderer using just the
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functional language...)
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.PP
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The standard input can be specified with a hyphen ('-').
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A command that produces a RADIANCE picture can be given in place of a file
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by preceeding it with an exclamation point ('!').
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.SH EXAMPLES
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To produce a picture showing the difference between pic1 and pic2:
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.IP "" .2i
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pcomb -e 'ro=ri(1)-ri(2);go=gi(1)-gi(2);bo=bi(1)-bi(2)' pic1 pic2 > diff
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.PP
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Or, more efficiently:
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.IP "" .2i
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pcomb pic1 -s -1 pic2 > diff
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.PP
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To precompute the gamma correction for a picture:
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.IP "" .2i
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pcomb -e 'ro=ri(1)^.4;go=gi(1)^.4;bo=bi(1)^.4' pic > pic.gam
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.PP
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To perform some special filtering:
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.IP "" .2i
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pcomb -f myfilt.cal -x xmax/2 -y ymax/2 input.pic > filtered.pic
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.PP
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To make a picture of a dot:
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.IP "" .2i
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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
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.SH AUTHOR
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Greg Ward
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.SH "SEE ALSO"
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getinfo(1), icalc(1), pcompos(1), pfilt(1), rpict(1)
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