1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>6.7. Unsharp Mask</title>
<link rel="stylesheet" href="gimp-help-plain.css" type="text/css" />
<link rel="stylesheet" href="gimp-help-screen.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.66.1" />
<link rel="start" href="index.html" title=" " />
<link rel="up" href="ch06s06.html" title="6. Enhance filters" />
<link rel="prev" href="ch06s06s06.html" title="6.6. Sharpen" />
<link rel="next" href="ch06s07.html" title="7. Generic filters" />
</head>
<body>
<div xmlns="" class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center" id="chaptername">6.7. Unsharp Mask</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="ch06s06s06.html">Prev</a> </td>
<th width="60%" align="center" id="sectionname">6.7. Unsharp Mask</th>
<td width="20%" align="right"> <a accesskey="n" href="ch06s07.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="plug-in-unsharp-mask"></a>6.7. Unsharp Mask</h3>
</div>
</div>
</div>
<a id="id3362771" class="indexterm"></a>
<div class="mediaobject">
<img src="../images/filters/filters-enhance-unsharpmask.png" />
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3363434"></a>Overview</h4>
</div>
</div>
</div>
<p>
This filter is found in
<span class="guimenuitem">Image>Filters/Enhance/<span class="accel">U</span>nsharp Mask</span>
</p>
<p>
Out-of-focus photographs but also most of digitized images need
correction of sharpness. This is due to digitizing process that
must chop a color continuum up in points with slightly different
colors: elements thiner than sampling frequency will be averaged
into an uniform color. So sharp borders are rendered a little
blurred. The same phenomenon appears when printing color dots on
paper.
</p>
<p>
The Unsharp Mask filter (what an odd name!) sharpens edges of the
elements without increasing noise or blemish. It is the king of
the sharpen filters.
</p>
<p>
Some scanners apply a sharpen filter while scanning. It's worth to
disable it so that you keep control on your image.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3362731"></a>Options</h4>
</div>
</div>
</div>
<div class="variablelist">
<dl>
<dt>
<span class="term">Parameters setting</span>
</dt>
<dd>
<p>
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="guilabel">Radius</span>: slider and input boxes
(0.1-120) allow you to set how many pixels on either
side of an edge will be affected by sharpening. High
resolution images allow higher radius. Y'd better to
always sharpen an image at its final resolution.
</p>
</li>
<li>
<p>
<span class="guilabel">Amount</span>: slider and input boxes
(0.00-5.00) allow you to set strength of sharpening.
</p>
</li>
<li>
<p>
<span class="guilabel">Threshold</span>: slider and input boxes
(0-255) allow you to set the minimum difference in pixel
values that indicates an edge where sharpen must be
applied. So you can protect areas of smooth tonal
transition from sharpening, and avoid creation of
blemishes in face, sky or water surface.
</p>
</li>
</ul>
</div>
<p>
</p>
</dd>
</dl>
</div>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3363656"></a>More informations</h4>
</div>
</div>
</div>
<p>
To prevent color distorsion while sharpening, Decompose your
image to HSV and work only on Value. Then Compose the image
to HSV. This is well explained at <a href="http://www.gimpguru.org" target="_top">gimpguru.org</a>
</p>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="ch06s06s06.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="ch06s06.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="ch06s07.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">6.6. Sharpen </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> 7. Generic filters</td>
</tr>
</table>
</div>
</body>
</html>
|
