pcomb - combine RADIANCE pictures. |

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

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 (+/- 8 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. 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 -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 ('!'). |

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' pic > pic.gam |

To perform some special filtering: |

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

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 |

Greg Ward |

calc(1), getinfo(1), pcompos(1), pfilt(1), rpict(1) |

https://www.schorsch.com/en/software/rayfront/manual/htmlman/pcomb.html

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Copyright © 2004-2018 schorsch.com