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<!--
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// Copyright (C) 2002-2020 Thomas S. Ullrich
//
// This file is part of "xyscan".
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// This file may be used under the terms of the GNU General Public License.
// This project is free software; you can redistribute it and/or modify it
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// Author: Thomas S. Ullrich
// Last update: Feb 26, 2020
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<html>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
<title>Density Histogram</title>
<body style="font-family: Arial, Helvetica, sans-serif, Geneva">
<h2>Density Histogram</h2>
<p align="left">
To aid placing the markers and, in some cases, improve the scan quality the <em>Density Histogram</em> can be used. It depicts the grayscale density<sup>1</sup> of the pixels along the horizontal and vertical cursor axis at the current position. Pixel 0 is the actual cursor position. The histogram covers ±5 pixels to the left (up) and right (down) of the current position. This is especially useful for fine adjustments with <code>Alt (Option) + arrow</code>. Launch it via <code>View->Density Histogram</code> or Ctrl+G (macOS: ⌘+G). By default the pixel along the horizontal (red) and vertical (blue) axis are shown. A pull-down menu in the upper left allows to hide either the horizontal or vertical axis density.
</p>
<div align="center">
<p><img src="histo.png" width="323" border="0" /></p>
</div>
<p><sup>1</sup> The grayscale density is obtained by converting a pixel into its grayscale equivalent and inverting the value so that high numbers indicate higher densities (blacker). White has a value of 0 and black is 255.</p>
</body>
</html>
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