---
name: "pfilt"
section: "1"
platform: "linux"
package: "radiance"
version: "4R1+20120125-1+b1"
release: "Debian 7 (Wheezy)"
platforms: ["linux"]
url: "https://new.carta.tech/pfilt"
---

# pfilt(1)

filter a RADIANCE picture

## NAME

pfilt - filter a RADIANCE picture

## SYNOPSIS

**pfilt** \[ **options** \] \[ **file** \]

## DESCRIPTION

*Pfilt* performs anti-aliasing and scaling on a RADIANCE picture. The program makes two passes on the picture file in order to set the exposure to the correct average value. If no *file* is given, the standard input is read.

- **-x** *res*

  Set the output x resolution to *res.* This must be less than or equal to the x dimension of the target device. If *res* is given as a slash followed by a real number, the input resolution is divided by this number to get the output resolution. By default, the output resolution is the same as the input.

- **-y** *res*

  Set the output y resolution to *res,* similar to the specification of the x resolution above.

- **-p** *rat*

  Set the pixel aspect ratio to *rat.* Either the x or the y resolution will be reduced so that the pixels have this ratio for the specified picture. If *rat* is zero, then the x and y resolutions will adhere to the given maxima. Zero is the default.

- **-c**

  Pixel aspect ratio is being corrected, so do not write PIXASPECT variable to output file.

- **-e** *exp*

  Adjust the exposure. If *exp* is preceded by a '+' or '-', the exposure is interpreted in f-stops (ie. the power of two). Otherwise, *exp* is interpreted as a straight multiplier. The individual primaries can be changed using *-er,* *-eg* and *-eb.* Multiple exposure options have a cumulative effect.

- **-t** lamp

  Color-balance the image as if it were illuminated by fixtures of the given type. The specification must match a pattern listed in the lamp lookup table (see the -f option below).

- **-f** lampdat

  Use the specified lamp lookup table rather than the default (lamp.tab).

- **-1**

  Use only one pass on the file. This allows the exposure to be controlled absolutely, without any averaging. Note that a single pass is much quicker and should be used whenever the desired exposure is known and star patterns are not required.

- **-2**

  Use two passes on the input. This is the default.

- **-b**

  Use box filtering (default). Box filtering averages the input pixels corresponding to each separate output pixel.

- **-r** *rad*

  Use Gaussian filtering with a radius of *rad* relative to the output pixel size. This option with a radius around 0.6 and a reduction in image width and height of 2 or 3 produces the highest quality pictures. A radius greater than 0.7 results in a defocused picture.

- **-m** *frac*

  Limit the influence of any given input pixel to *frac* of any given output pixel. This option may be used to mitigate the problems associated with inadequate image sampling, at the expense of a slightly blurred image. The fraction given should not be less than the output picture dimensions over the input picture dimensions (x\_o\*y\_o/x\_i/y\_i), or blurring will occur over the entire image. This option implies the *-r* option for Gaussian filtering, which defaults to a radius of 0.6.

- **-h** *lvl*

  Set intensity considered \`\`hot'' to *lvl.* This is the level above which areas of the image will begin to exhibit star diffraction patterns (see below). The default is 100 watts/sr/m2.

- **-n** *N*

  Set the number of points on star patterns to *N.* A value of zero turns star patterns off. The default is 0. (Note that two passes are required for star patterns.)

- **-s** *val*

  Set the spread for star patterns to *val.* This is the value a star pattern will have at the edge of the image. The default is .0001.

- **-a**

  Average hot spots as well. By default, the areas of the picture above the hot level are not used in setting the exposure.

## ENVIRONMENT

RAYPATH		directories to search for lamp lookup table

## FILES

/tmp/rt??????

## AUTHOR

Greg Ward

## SEE ALSO

[getinfo(1)](/getinfo/1.md), [ies2rad(1)](/ies2rad/1.md), [pcompos(1)](/pcompos/1.md), [pflip(1)](/pflip/1.md), [pinterp(1)](/pinterp/1.md), [pvalue(1)](/pvalue/1.md), [protate(1)](/protate/1.md), [rad(1)](/rad/1.md), [rpict(1)](/rpict/1.md), [ximage(1)](/ximage/1.md)