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| author | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
|---|---|---|
| committer | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
| commit | 90ae43f347fe4075f76a5f37d011d39bd4c10ddd (patch) | |
| tree | a04fa64e893f21a07ed19704121e626877f4aef6 /docs/aggpas/gamma_correction.html | |
| parent | 88f1fc9acda900eecfcfc884a60e4958145e3fc0 (diff) | |
| download | fpGUI-90ae43f347fe4075f76a5f37d011d39bd4c10ddd.tar.xz | |
adds AGG docs in general.
These docs give you lots of background information on the working
of the AGG (Anti-Grain Geometry) library and how it works.
Using the knowledge you learn from this, you will be able to extend
the TAgg2D canvas for your own needs and applications.
Diffstat (limited to 'docs/aggpas/gamma_correction.html')
| -rw-r--r-- | docs/aggpas/gamma_correction.html | 245 |
1 files changed, 245 insertions, 0 deletions
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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