diff options
| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2017-05-18 18:31:03 +0000 |
|---|---|---|
| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2017-05-18 18:31:03 +0000 |
| commit | 4e1337c38b24ebad6e840055bba85d55c9e717ae (patch) | |
| tree | 9684723206258067fa99c53643630906c63b374e /pamgauss.html | |
| parent | 09f3f2d31192d4e787e3fc5df7d485aa8f9bbed7 (diff) | |
| download | netpbm-mirror-4e1337c38b24ebad6e840055bba85d55c9e717ae.tar.gz netpbm-mirror-4e1337c38b24ebad6e840055bba85d55c9e717ae.tar.xz netpbm-mirror-4e1337c38b24ebad6e840055bba85d55c9e717ae.zip | |
miscellaneous update
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@2976 9d0c8265-081b-0410-96cb-a4ca84ce46f8
Diffstat (limited to 'pamgauss.html')
| -rw-r--r-- | pamgauss.html | 101 |
1 files changed, 73 insertions, 28 deletions
diff --git a/pamgauss.html b/pamgauss.html index f3bd38e2..48725823 100644 --- a/pamgauss.html +++ b/pamgauss.html @@ -2,13 +2,13 @@ <HTML><HEAD><TITLE>Pamgauss User Manual</TITLE></HEAD> <BODY> <H1>pamgauss</H1> -Updated: 8 May 2004 +Updated: 18 May 2017 <BR> <A HREF="#index">Table Of Contents</A> <H2>NAME</H2> -pamgauss - create a two dimensional gaussian function as a PAM image +<b>pamgauss</b> - create a two-dimensional Gaussian function as a PAM image <H2 id="synopsis">SYNOPSIS</H2> @@ -18,6 +18,8 @@ pamgauss - create a two dimensional gaussian function as a PAM image <b>-sigma=</b><i>number</i> [<b>-maxval=</b><i>number</i>] [<b>-tupletype=</b><i>string</i>] +[<b>-maximize</b>] +[<b>-oversample=</b><i>number</i> <p>Minimum unique abbreviation of option is acceptable. You may use double @@ -28,8 +30,8 @@ space in place of the equals sign to separate an option name from its value. <H2 id="examples">EXAMPLES</H2> <pre> - pamgauss 3 3 -sigma=.5 -tupletype=GRAYSCALE | pamtopnm >gauss.pgm - pnmconvol -nooffset gauss.pgm myimage.ppm >blurred.ppm + pamgauss 7 7 -sigma=.5 -maximize -tupletype=GRAYSCALE | pamtopnm >gauss.pgm + pnmconvol -nooffset -normalize gauss.pgm myimage.ppm >blurred.ppm </pre> <H2 id="description">DESCRIPTION</H2> @@ -37,27 +39,20 @@ space in place of the equals sign to separate an option name from its value. <p>This program is part of <a href="index.html">Netpbm</a>. <p><b>pamgauss</b> generates a one-plane PAM image whose samples are a -gaussian function of their distance from the center of the image. I.e. +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. -<p>The values are scaled so that the volume under the surface of the -two-dimensional Gaussian function is the maxval of the image. - <p>You can use this image as a convolution kernel with <b>pnmconvol</b> to blur an image. (This technique is known as Gaussian blurring). <i>width</i> and <i>height</i> are the dimensions of the image that -<b>pamgauss</b> generates. Mathematically speaking, they are the domain -of the two dimensional gaussian function. - -<p>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. If you want to be sure you get a whole -Gaussian function, make sure that you choose a sigma and image -dimensions so that if you made it any larger, the sample values at the -edges would be zero. +<b>pamgauss</b> 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. <p>The output image is PAM. To make it usable with <b>pnmconvol</b>, specify <b>-tupletype=GRAYSCALE</b> so <b>pnmconvol</b> can use it as @@ -65,23 +60,62 @@ if it were PGM. You must use the <b>-nooffset</b> option on <b>pnmconvol</b> because zero means zero in the PAM that <b>pamgauss</b> generates. +<p>Without <b>-maximize</b>, 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. + +<p><b>pamgauss</b> 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, <b>pamgauss</b> 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. + + <H2 id="options">OPTIONS</H2> <dl> <dt><b>-sigma=</b><i>number</i> -<dd>This is the sigma parameter of the Gaussian function (if it were a -Gaussian probability function, this would be its standard deviation). -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. +<dd>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. -<p><i>number</i> is in units of pixels. +<p><i>number</i> is in units of samples. <p>This option is required. There is no default. +<dt><b>-maximize</b> +<dd>Causes <b>pamgauss</b> 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. +<p> +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 +<b>pnmconvol</b>'s <b>-normalize</b> option. The reason this is different +from just not using <b>-maximize</b> is that this subsequent normalization can +be done with much more precision than can be represented in a PAM image. +<p> +Without this option, <b>pamgauss</b> 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. + +<p>This option was new in Netpbm 10.79 (June 2017). + <dt><b>-maxval=</b><i>number</i> -<dd>This is the maxval for the output image. It defaults to 255. +<dd>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. + +<p>The default is 255. <dt><b>-tupletype=</b><i>string</i> <dd> @@ -89,10 +123,22 @@ 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, <b>pamgauss</b> generates a PAM with unspecified tuple type. +<dt><b>-oversample=</b><i>number</i> +<dd> +<p>This sets the oversampling factor. <b>pamgauss</b> samples the +Gaussian function this many times, bother horizontally and vertically, to +get the value of each sample in the output. + +<p>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. + +<p>The default is 5 divided by the standard deviation, rounded up to a whole +number. + </dl> -<A NAME="seealso"> </A> -<H2>SEE ALSO</H2> +<H2 id="seealso">SEE ALSO</H2> <B><A HREF="pnmconvol.html">pnmconvol</A></B>, <B><A HREF="pamtopnm.html">pamtopnm</A></B>, @@ -100,8 +146,7 @@ It can be any string up to 255 characters. If you don't specify this, <B><A HREF="pamseq.html">pamseq</A></B>, <B><A HREF="pam.html">pam</A></B> -<A NAME="history"> </A> -<H2>HISTORY</H2> +<H2 id="history">HISTORY</H2> <p><b>pamgauss</b> was new in Netpbm 10.23 (July 2004). |