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diff --git a/docs/aggpas/gamma_correction.html b/docs/aggpas/gamma_correction.html new file mode 100644 index 00000000..e5c91926 --- /dev/null +++ b/docs/aggpas/gamma_correction.html @@ -0,0 +1,245 @@ +<html><head><title>Anti-Grain Geometry - Gamma Correction</title> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<link rel="stylesheet" type="text/css" +href="gamma_correction_files/agg.css"> +</head><body><a name="PAGE_GAMMA_CORRECTION"><b></b></a> + + +<table style="margin: 0px;" height="1px" width="640px" border="0" +cellpadding="0" cellspacing="0"> +<tbody><tr> +<td bgcolor="#583927"></td> +</tr> +</tbody></table> +<table style="margin: 0px;" width="640px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr> +<td> +<table style="margin: 0px;" width="170px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr><td><a href="http://www.antigrain.com/index.html" +class="mpmenu">Home/</a></td></tr> +<tr><td><a href="http://www.antigrain.com/research/index.html" +class="mpmenu">Research/</a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +</tbody></table> +</td> +<td width="1px" bgcolor="#583927"></td> +<td style="text-align: right;" valign="top" width="450px"> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr> +<td><img src="gamma_correction_files/agg_logo.gif" border="0"></td> +</tr> +<tr> +<td> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr height="15px"> +<td> <a class="topmenu" +href="http://www.antigrain.com/news/index.html">News</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/doc/index.html">Docs</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/download/index.html">Download</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/maillist/index.html">Mailing List</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/cvs/index.html">CVS</a> </td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p> +</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><h1>Gamma Correction<span +class="subtitle"><br>Using Gamma Correction in Anti-Aliasing</span></h1></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Aliasing</nobr></b> + technology is always difficult. The difficulty here +is not only in algorithms, but also because the visual quality of +the image depends on the displaying equipment. <b><nobr>Anti-Aliasing</nobr></b> + images look +differently on CRT monitors and on LCD ones. In general it's a +science (or maybe even art) called Color Management. +<b><nobr>Anti-Grain</nobr> Geometry</b> uses the approach of <b><nobr>Anti-Aliasing</nobr></b> + that potentially allows us to +obtain the best result. The rendering procedure calculates the +exact coverage values for every boundary pixel and as a result +one can have any number of <b><nobr>Anti-Aliasing</nobr></b> levels. +<b><nobr>Anti-Grain</nobr> Geometry</b> uses 256 levels which is quite +enough for any practical +purpose and much better than 5-level <b><nobr>Anti-Aliasing</nobr></b> +used in many applications, +for example, True-Type font renderers, almost all +<a href="http://www.adobe.com/"><img +src="gamma_correction_files/link.gif" border="0">Adobe</a> products and +so on. +I was absolutely sure that the rendering method I use gives +the best result. But when I tried to render the same image +with <b><nobr>Anti-Grain</nobr> Geometry</b> and <a +href="http://www.adobe.com/svg/"><img +src="gamma_correction_files/link.gif" border="0">Adobe SVG Viewer</a> +I found out that the Adobe SVG Viewer uses only 5 levels of <b><nobr>Anti-Aliasing</nobr></b>, + +but the result sometimes looks better than in <b><nobr>Anti-Grain</nobr> + Geometry</b>.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><img + src="gamma_correction_files/gamma_lion1.jpg" title="" border="0"><!----> + <img src="gamma_correction_files/gamma_lion2.jpg" +title="" border="0"><!----></p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +left image is rendered with <b><nobr>Anti-Grain</nobr> Geometry</b>, the + right one with the +<a href="http://www.adobe.com/svg/"><img +src="gamma_correction_files/link.gif" border="0">Adobe SVG Viewer</a>. +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +lion's moustache look smoother when rendering with 5-level +Adobe SVG Viewer, al least on CRT monitors. But still, the enlarged +images show us the lack of the <b><nobr>Anti-Aliasing</nobr></b> levels +used in Adobe Viewer.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><img + src="gamma_correction_files/gamma_lion1e.jpg" title="" border="0"><!----> + <img src="gamma_correction_files/gamma_lion2e.jpg" +title="" border="0"><!----></p></td></tr></tbody></table> + +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><img + src="gamma_correction_files/gamma.gif" title="" style="border-color: +rgb(255, 255, 255);" align="left" border="4"><!----> +Obviously, <b><nobr>Anti-Grain</nobr> Geometry</b> can render better, +but using a simple linear dependance +Pixel Coverage <span class="larger">→</span> Brightness is not the best +and should be corrected. +In color management it's called Gamma Correction. For gamma correction +I use a simple array of 256 values that give the desired value of +brightness +depending on the pixel coverage. If all the values in the array are +equal +to their index, i.e., 0,1,2,3,4,… it means that there's no gamma +correction. +The array can be calculated using any approach, but the simplest method +is to use a B-Spline curve with two reference points and four +coeffitiens +(kx1, ky1, kx2, ky2) that determine its shape. So, I created an +application +with a special gamma correction control that allows for calculation of +the +array of the gamma values. +It draws 6 very narrow ellipses, 6 circles and some other figures that +can be used as a visual test of the quality of <b><nobr>Anti-Aliasing</nobr></b>. +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gamma_correction_files/gamma1.gif" title="Default Shape - No Gamma +Correction" border="0"><br><i>Default Shape - No Gamma Correction</i></center></td></tr></tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +control points can be moved inside their quadrants. +The following image looks much better at least on CRT monitors.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gamma_correction_files/gamma2.gif" title="Gamma Correction for CRT +Monitors" border="0"><br><i>Gamma Correction for CRT Monitors</i></center></td></tr></tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>We +actually can obtain much better result of certain thickness and +brightness, but it cannot be used for general case. The shown above +example is a kind of an average case which is not the best for certain +parameters, but gives us rather a good average result on CRT monitors, +as well as on LCD ones. Below are the examples of other shapes of the +gamma curve.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gamma_correction_files/gamma3.gif" title="Test Gamma 1" border="0"><br><i>Test + Gamma 1</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td><center><img +src="gamma_correction_files/gamma4.gif" title="Test Gamma 2" border="0"><br><i>Test + Gamma 2</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td><center><img +src="gamma_correction_files/gamma5.gif" title="Test Gamma 3" border="0"><br><i>Test + Gamma 3</i></center></td></tr></tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Besides, + the gamma correction strongly depends on the content of the image. +The values that are good enough for rendering ellipses like shown above +may give a very bad result when rendering small text glyphs. The latest +require sharper forms, while large geometric figures look better with +very smooth edges. +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Finally, + this is the result of rendering the same lion with gamma correction +for CRT monitors. Now it looks better than the one rendered with Adobe +SVG Viewer.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><img + src="gamma_correction_files/gamma_lion3.jpg" title="" border="0"><!----> + <img src="gamma_correction_files/gamma_lion3e.jpg" +title="" border="0"><!----></p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>You +can download the working application for Windows: +<a +href="http://www.antigrain.com/research/gamma_correction/gamma_ctrl.zip"><img + src="gamma_correction_files/download.gif" border="0">Gamma Control + (gamma_ctrl.zip)</a></p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +source code can be found in the <code>examples</code> directory of the +distribution package. Visit the <a +href="http://www.antigrain.com/download/index.html#PAGE_DOWNLOAD">Download</a> + page.</p></td></tr></tbody></table> + + +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr><td><center><span class="authors"> +Copyright <span class="larger">©</span> 2002-2006 +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +<tr><td><center><span class="authors"> +Web Design and Programming +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +</tbody></table> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +</body></html>
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