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diff --git a/pfm.html b/pfm.html index 5f91674d..2ea670b5 100644 --- a/pfm.html +++ b/pfm.html @@ -5,7 +5,7 @@ </head> <body> <h1>pfm</h1> -Updated: 19 April 2012 +Updated: 27 February 2024 <h2>NAME</h2> PFM - PFM graphic image file format @@ -17,14 +17,20 @@ This document describes the PFM graphic image file format as understood by the Netpbm converters <a href="pamtopfm.html"><b>pamtopfm</b></a> and <a href="pfmtopam.html"><b>pfmtopam</b></a>. -<p>There are multiple similar formats known as PFM in the world, none -of them authoritatively documented. The format described here is one -that Bryan Henderson deduced from a program he found somewhere that -dealt with a "PFM" format. +<p>There are multiple similar formats known as PFM in the world, none of them +authoritatively documented. The format described here is one that Bryan +Henderson deduced from a program he found somewhere that dealt with a "PFM" +format. This format appears to be the one Gimp calls PFM. -<p>The PFM format is inspired by the Netpbm formats, and you will see -lots of similarity. It is not, however, an official Netpbm format. -Its goal is not consistent with those of Netpbm formats. +Another important PFM is used by Adobe Photoshop and appears to be identical +to this except that rows are ordered from top to bottom in the Adobe version. +If you interchange images between systems that use these two formats, it will +work except that your image gets flipped upside down. You can compensate for +that with <kbd>pamflip -topbottom</kbd>. + +<p>The PFM format is inspired by the Netpbm formats, and you will see lots of +similarity. It is not, however, an official Netpbm format. Its goal is not +consistent with those of Netpbm formats. <h2>The format</h2> @@ -75,6 +81,10 @@ square meter. delimiters of any kind. They are grouped by row, with the pixels in each row ordered left to right and the rows ordered bottom to top. +<em>Note:</em> This is the opposite of Netpbm formats, which order rows +top to bottom. It is also the opposite of the format Adobe Photoshop calls +PFM. See the introduction for more information on this disparity. + <p>Each pixel consists of 1 or 3 samples, packed one after another, with no delimiters of any kind. 1 sample for a grayscale PFM and 3 for a color PFM (see the Identifier Line of the PFM header). |