# pamgauss - Man Page

create a two-dimensional Gaussian function as a PAM image

## Synopsis

**pamgauss** *width height* **-sigma=***number* [**-maxval=***number*] [**-tupletype=***string*] [**-maximize**] [**-oversample=***number*]

Minimum unique abbreviation of option is acceptable. You may use double hyphens instead of single hyphen to denote options. You may use white space in place of the equals sign to separate an option name from its value.

## Examples

pamgauss 7 7 -sigma=.5 -maximize -tupletype=GRAYSCALE | pamtopnm >gauss.pgm pnmconvol -nooffset -normalize gauss.pgm myimage.ppm >blurred.ppm

## Description

This program is part of **Netpbm**(1).

**pamgauss** generates a one-plane PAM image whose samples are a Gaussian function of their distance from the center of the image. I.e. the sample value is highest in the center and goes down, in a bell curve shape, as you move away from the center.

You can use this image as a convolution kernel with **pnmconvol** to blur an image. (This technique is known as Gaussian blurring).

*width* and *height* are the dimensions of the image that **pamgauss** generates. Mathematically speaking, they are the domain of the two-dimensional Gaussian function. If you want to be sure you get a whole Gaussian function, make sure that you choose a standard deviation and image dimensions so that if you made it any larger, the sample values at the edges would be zero.

The output image is PAM. To make it usable with **pnmconvol**, specify **-tupletype=GRAYSCALE** so **pnmconvol** can use it as if it were PGM. You must use the **-nooffset** option on **pnmconvol** because zero means zero in the PAM that **pamgauss** generates.

Without **-maximize**, the sum of all the samples is equal to the image's maxval (within rounding error). This is true even if you clip the Gaussian function by making the image too small. This is what is normally required of a convolution kernel.

**pamgauss** oversamples and averages to represent the continuous Gaussian function in discrete samples in the PAM output. Consider an image 11 samples wide and an oversampling factor of 10. The samples can be thought of as contiguous squares one unit wide. The center of the image is thus the center of the 6th sample from the left. The 3rd sample from the left covers a range of distances from 3 to 4 units from the center of the image. Because the oversampling factor is 10, **pamgauss** computes the value of the Gaussian function at 10 points evenly spaced between 3 and 4 units from the center of the image and assigns the 3rd sample from the left the mean of those 10 values.

## Options

In addition to the options common to all programs based on libnetpbm (most notably **-quiet**, see Common Options ), **pamgauss** recognizes the following command line options:

- -sigma=
*number* This is the standard deviation of the Gaussian function. The higher the number, the more spread out the function is. Normally, you want to make this number low enough that the function reaches zero value before the edge of your image.

*number*is in units of samples.This option is required. There is no default.

- -maximize
Causes

**pamgauss**to use the whole dynamic range available in the output PAM image by choosing an amplitude for the Gaussian function that causes the maximum value in the image to be the maxval of the image.If you select this, you probably want to normalize the output (scale the samples down so the volume under the surface of the two-dimensional Gaussian function is the maxval) before you use it, for example with

**pnmconvol**'s**-normalize**option. The reason this is different from just not using**-maximize**is that this subsequent normalization can be done with much more precision than can be represented in a PAM image.Without this option,

**pamgauss**uses an amplitude that makes the volume under the surface of the two-dimensional Gaussian function the maxval of the image. This means all the samples in the image are normally considerably less than the maxval.This option was new in Netpbm 10.79 (June 2017).

- -maxval=
*number* This is the maxval for the output image. 65535 is almost always the best value to use. But there may be some programs (not part of Netpbm) that can't handle a maxval greater than 255.

The default is 255.

- -tupletype=
*string* This is the value of the "tuple_type" attribute of the created PAM image. It can be any string up to 255 characters.

If you don't specify this,

**pamgauss**generates a PAM with unspecified tuple type.- -oversample=
*number* This sets the oversampling factor.

**pamgauss**samples the Gaussian function this many times, both horizontally and vertically, to get the value of each sample in the output.An oversampling factor of 1 means no oversampling, which means each sample is based only on the value of the Gaussian function at the center of the sample.

The default is 5 divided by the standard deviation, rounded up to a whole number.

This option was new in Netpbm 10.79 (June 2017). Before that, it is essentially 1 - there is no oversampling.

## See Also

pnmconvol(1), pamtopnm(1), pgmkernel(1), pamseq(1), **pam**(1)

## History

**pamgauss** was new in Netpbm 10.23 (July 2004).

## Document Source

This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master documentation is at