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diff --git a/pamtilt.html b/pamtilt.html new file mode 100644 index 00000000..e5e0566a --- /dev/null +++ b/pamtilt.html @@ -0,0 +1,175 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML><HEAD><TITLE>Pamtilt User Manual</TITLE></HEAD> +<BODY> +<H1>pamtilt</H1> +Updated: 28 August 2005 +<BR> +<A HREF="#index">Table Of Contents</A> + +<H2 id="name">NAME</H2> +pamtilt - print the tilt angle of a PGM file + +<H2 id="synopsis">SYNOPSIS</H2> + +<b>pamtilt</b> +[<b>-angle=</b><i>maxangle</i>] +[<b>-fast</b>] +[<b>-quality=</b><i>q</i> +[<b>-hstep=</b><i>n</i>] +[<b>-vstep=</b><i>n</i>] +<br> +[<b>-dstep=</b><i>n</i>] +[<b>-astep=</b><i>n</i>] +[<b>-verbose</b>] +[<i>pgmfile</i>] + +<h2 id="examples">EXAMPLES</h2> + +<pre> +<kbd> + scanimage --mode Gray --resolution 300 >crooked.pgm + pnmrotate -b white `pamtilt crooked.pgm` crooked.pgm >straight.pgm +</kbd> + (then crop, threshold, etc.) +</pre> + +<H2 id="description">DESCRIPTION</H2> + +<p>This program is part of <a href="index.html">Netpbm</a>. + +<p><b>pamtilt</b> tries to find the correct angle for untilting +(de-skewing) a scanned text document. The output is a single +floating-point number (the angle in degrees) for use as the argument +to pnmrotate. + +<p>"Document skew" is the name given to what happens when +you feed a page into an image scanner at an angle: the resulting image +is tilted. <b>pamtilt</b> aims to correct that. + +<p><b>pamtilt</b> makes three iterations at successively finer +increments, testing prospective rotation angles to find the best one. +<b>pamtilt</b> works best for straightening images with strong +horizontal lines and does poorly with arbitrary photos. If +<b>pamtilt</b> has no confidence in its results, it prints the special +value 00.00; you can check for this or just pass it as a legal +argument to pnmrotate. + +<p><b>pamtilt</b> operates on the first plane of the input image, +which is either PNM or PAM, and ignores any other planes. Ordinarily, +the input is PGM or GRAYSCALE PAM, so there is only one plane. + +<p><b>pamtilt</b> works on bilevel (PBM, BLACKANDWHITE PAM) images as +well as grayscale, but you will minimize artifacts if you scan and +rotate in grayscale before you apply a threshold to make a bilevel +image. + +<H2 id="options">OPTIONS</H2> + +<p>A few options have general utility: + +<DL COMPACT> + +<dt><b>-angle=</b><i>maxangle</i> + +<dd> +Assume a maximum tilt angle of <i>maxangle</i> (measured in degrees). +The default value is sufficient for most images, even those scanned +somewhat carelessly. + +<p>The default is 10.0. + +<dt><b>-fast</b> + +<dd> +Skip the third iteration for speed at the expense of accuracy. + +<dt><b>-verbose</b> +<dd> +Show on Standard Error the measurements computed at each tested angle. + +</dl> + +<p>Here are some other options you can use to tune the operation of +<b>pamtilt</b> but they're seldom needed. The default values +accommodate a wide variety of input documents. + +<dl> +<DT> +<B>-quality=</B><i>q</i> + +<dd>Require a signal-to-noise ratio of a least <i>q</i> on the first +iteration to report a valid result. Larger values reduce the chances +of obtaining a bogus result at the risk of obtaining no result at all. + +<p>The default is 1.0. + +<dt><b>-hstep=</b><i>n</i> +<dd> +Set the horizontal increment to check every <i>n</i>th column. This +value affects both run time and memory requirements. + +<p>The default is 11. + +<dt><b>-vstep=</b><i>n</i> + +<dd> +Set the vertical increment to check every nth row. Larger values +usually work, reducing run time, but they increase the risk of +incorrect results. + +<p>The default is 5. + +<dt><b>-dstep=</b><i>n</i> + +<dd> +Set the vertical distance used when checking pixels in a column. The +default is intended to minimize the effect of noise along a horizontal +boundary. + +<p>The default is 2. + +<dt><b>-astep=</b><i>n</i> + +<dd> +Set the angle increment of the first iteration, in degrees. + +<p>The default is 1.0. + +</dl> + + +<h2 id="references">REFERENCES</h2> + +<p><B>pamtilt</B> implements a somewhat simplified algorithm inspired +by: "Measuring Document Image Skew and Orientation", by Bloomberg, +Kopec, and Dasari. In SPIE Volume 2422, Document Recognition II, +pages 302-316, February 1995. + +<h2 id="seealso">SEE ALSO</h2> + +<ul> +<li><a href="pnmrotate.html"><b>pnmrotate</b></a> +<li><a href="pgm.html">pgm</a> +</ul> + +<h2 id="history">HISTORY</h2> + +<p><b>pamtilt</b> was new in Netpbm 10.30 (October 2005). + +<p>Gregg Townsend wrote it and sent it to Bryan Henderson in August +2005. Bryan recoded it to fit Netpbm conventions. + +<HR> +<A NAME="index"> </A> +<H2>Table Of Contents</H2> +<UL> +<LI><A HREF="#name">NAME</A> +<LI><A HREF="#synopsis">SYNOPSIS</A> +<LI><A HREF="#examples">EXAMPLES</A> +<LI><A HREF="#description">DESCRIPTION</A> +<LI><A HREF="#options">OPTIONS</A> +<LI><A HREF="#seealso">SEE ALSO</A> +<LI><A HREF="#history">HISTORY</A> +</UL> +</BODY> +</HTML> |