    imagecolorallocatealpha (PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)
imagecolorallocatealpha — Allocate a color for an image   Description imagecolorallocatealpha(
 GdImage $image,
 int $red,
 int $green,
 int $blue,
 int $alpha
): int|false  imagecolorallocatealpha() behaves identically to imagecolorallocate() with the addition of the transparency parameter alpha.    Parameters
  image
  A GdImage object, 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.  
WarningThis 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     8.0.0  image expects a GdImage instance now; previously, a resource was expected.       Examples  Example #1 Example of using imagecolorallocatealpha()  <?php
$size = 300;
$image=imagecreatetruecolor($size, $size);

// something to get a white background with black border
$back = imagecolorallocate($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;

// allocate colors with alpha values
$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);
$red    = imagecolorallocatealpha($image, 255, 0, 0, 75);
$blue   = imagecolorallocatealpha($image, 0, 0, 255, 75);

// 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:        Example #2 Convert typical alpha values for use with imagecolorallocatealpha()  Usually alpha values of 0 designate fully transparent pixels, and the alpha channel has 8 bits. To convert such alpha values to be compatible with imagecolorallocatealpha(), some simple arithmetic is sufficient:   <?php
$alpha8 = 0; // fully transparent
var_dump(127 - ($alpha8 >> 1));
$alpha8 = 255; // fully opaque
var_dump(127 - ($alpha8 >> 1));
?>  The above example will output:  
int(127)
int(0)
     See Also  imagecolorallocate() - Allocate a color for an image imagecolordeallocate() - De-allocate a color for an image   


    
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