imagecolorallocate
If you need to calculate the integer representation of a color with an alpha channel, without initialising an image and using the imagecolorallocatealpha function. Then this function might be of some help:
<?php
function alphaColor($hexColor,$alpha)
{
return bindec(decbin($alpha).decbin(hexdec($hexColor));
}
echo alphaColor("FFFFFF",127);
?>
imagecolorallocatealpha
(PHP 4 >= 4.3.2, PHP 5)
imagecolorallocatealpha — 为一幅图像分配颜色 + alpha
说明
int imagecolorallocatealpha
( resource $image
, int $red
, int $green
, int $blue
, int $alpha
)
imagecolorallocatealpha() 的行为和 imagecolorallocate() 相同，但多了一个额外的透明度参数 alpha ，其值从 0 到 127。0 表示完全不透明，127 表示完全透明。
如果分配失败则返回 FALSE。
Example#1 使用 imagecolorallocatealpha() 的例子
<?php
$size = 300;
$image=imagecreatetruecolor($size, $size);
// 用白色背景加黑色边框画个方框
$back = imagecolorallocate($image, 255, 255, 255);
$border = imagecolorallocate($image, 0, 0, 0);
imagefilledrectangle($image, 0, 0, $size - 1, $size - 1, $back);
imagerectangle($image, 0, 0, $size - 1, $size - 1, $border);
$yellow_x = 100;
$yellow_y = 75;
$red_x = 120;
$red_y = 165;
$blue_x = 187;
$blue_y = 125;
$radius = 150;
// 用 alpha 值分配一些颜色
$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);
$red = imagecolorallocatealpha($image, 255, 0, 0, 75);
$blue = imagecolorallocatealpha($image, 0, 0, 255, 75);
// 画三个交迭的圆
imagefilledellipse($image, $yellow_x, $yellow_y, $radius, $radius, $yellow);
imagefilledellipse($image, $red_x, $red_y, $radius, $radius, $red);
imagefilledellipse($image, $blue_x, $blue_y, $radius, $radius, $blue);
// 不要忘记输出正确的 header！
header('Content-type: image/png');
// 最后输出结果
imagepng($image);
imagedestroy($image);
?>
Note: 本函数需要 GD 2.0.1 或更高版本（推荐 2.0.28 及更高版本）。
add a note
User Contributed Notesimagecolorallocatealpha
fjoggen at gmail dot com
29-Nov-2007 11:19
29-Nov-2007 11:19
fairplay at gmail dot com
16-Nov-2007 07:13
16-Nov-2007 07:13
My output image is musch worser -- http://i8.tinypic.com/8g6sv29.png
What have I do wrong?
eric (at) junioronline.us
25-Jan-2006 05:41
25-Jan-2006 05:41
If you only wish to extract the alpha value for a color, you can simply extract it like so:
<?php
$color = imagecolorat($im, 50, 50);
$alpha = $color >> 24;
?>
It actually shifts off the first 24 bits (where 8x3 are used for each color), and returns the remaining 7 allocated bits (commonly used for alpha)
fchristl at hotmail dot com
20-Sep-2003 03:55
20-Sep-2003 03:55
Check out this Source, it's a little funny feature showing you, for what imagecolorallocatealpha() is used:
<?php
$im=imagecreatetruecolor(300,300);
$white=imagecolorallocate($im,255,255,255);
imagefilledrectangle($im,0,0,imagesx($im),imagesy($im),$white);
for($i=0;$i<256;$i=$i+10)
{
$col=imagecolorallocatealpha($im,$i,$i,$i,ceil(rand(0,127)));
imagefilledellipse($im,$i,$i,$i,$i,$col);
}
header("content-type: image/png");
imagepng($im);
?>