Source

libgd 2.0 / alphachanneltest.html

Full commit
<head>
<title>gd Alpha Channel Test</title>
<head>
<body bgcolor="#c0c0FF">
<h1>gd Alpha Channel Test</h1>
If your browser fully supports PNG alpha channels, the
"blended" and "alpha channel" images should appear identical
to the naked eye. Miniscule mathematical differences may
exist due to the 7-bit alpha channel resolution of gd. 
<p>
Palette and truecolor images will look slightly different,
as the palette versions are limited to 256 palette entries,
which are used as well as possible to approach the effect
of the original truecolor version.
<table>
<tr>
<th colspan=2>Truecolor Images</th>
<tr>
<th>Blending against light blue, Half Size<td><img src="blending-halfsize-truecolor.png">
<tr>
<th>Alpha channel, Half Size<td><img src="noblending-halfsize-truecolor.png">
<tr>
<th>Blending against light blue, Full Size<td><img src="blending-fullsize-truecolor.png">
<tr>
<th>Alpha channel, Full Size<td><img src="noblending-fullsize-truecolor.png">
<tr>
<th>Blending against light blue, Double Size<td><img src="blending-doublesize-truecolor.png">
<tr>
<th>Alpha channel, Double Size<td><img src="noblending-doublesize-truecolor.png">
<tr>
<th colspan=2>Palette Images</th>
<tr>
<th>Blending against light blue, Half Size<td><img src="blending-halfsize-palette.png">
<tr>
<th>Alpha channel, Half Size<td><img src="noblending-halfsize-palette.png">
<tr>
<th>Blending against light blue, Full Size<td><img src="blending-fullsize-palette.png">
<tr>
<th>Alpha channel, Full Size<td><img src="noblending-fullsize-palette.png">
<tr>
<th>Blending against light blue, Double Size<td><img src="blending-doublesize-palette.png">
<tr>
<th>Alpha channel, Double Size<td><img src="noblending-doublesize-palette.png"></table>
</body>