imagecolorallocatealpha

(PHP 4 >= 4.3.2, PHP 5)

imagecolorallocatealphaAllocate a color for an image

Description

int imagecolorallocatealpha ( resource $image , int $red , int $green , int $blue , int $alpha )

imagecolorallocatealpha() behaves identically to imagecolorallocate() with the addition of the transparency parameter alpha.

Parameters

image

An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().

red

Value of red component.

green

Value of green component.

blue

Value of blue component.

alpha

A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.

The red, green and blue parameters are integers between 0 and 255 or hexadecimals between 0x00 and 0xFF.

Return Values

A color identifier or FALSE if the allocation failed.

Warning

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

Changelog

Version Description
5.1.3 Returns FALSE if the allocation failed. Previously -1 was returned.

Examples

Example #1 Example of using imagecolorallocatealpha()

<?php
$size 
300;
$image=imagecreatetruecolor($size$size);

// something to get a white background with black border
$back imagecolorallocate($image255255255);
$border imagecolorallocate($image000);
imagefilledrectangle($image00$size 1$size 1$back);
imagerectangle($image00$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;

// allocate colors with alpha values
$yellow imagecolorallocatealpha($image255255075);
$red    imagecolorallocatealpha($image2550075);
$blue   imagecolorallocatealpha($image0025575);

// drawing 3 overlapped circle
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);

// don't forget to output a correct header!
header('Content-Type: image/png');

// and finally, output the result
imagepng($image);
imagedestroy($image);
?>

The above example will output something similar to:

Output of example : Example of using imagecolorallocatealpha()

Notes

Note: This function requires GD 2.0.1 or later (2.0.28 or later is recommended).

See Also

Коментарии

If you only wish to extract the alpha value for a color, you can simply extract it like so:

<?php

    $color 
imagecolorat($im5050);
   
$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)
2006-01-25 03:41:16
http://php5.kiev.ua/manual/ru/function.imagecolorallocatealpha.html
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);
?>
2007-11-29 09:19:55
http://php5.kiev.ua/manual/ru/function.imagecolorallocatealpha.html
Автор:
When working with transparency, avoid imagecreate() and use imagecreatetruecolor() instead. Transparency effects may not work as expected within a palette-based image.
2015-09-23 01:30:41
http://php5.kiev.ua/manual/ru/function.imagecolorallocatealpha.html

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