imagecolorallocatealpha

Allocate a color for an image

&reftitle.description; ``int``false```imagecolorallocatealpha` `GdImage` `image` `int` `red` `int` `green` `int` `blue` `int` `alpha`

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

&reftitle.parameters;

&gd.image.description;

`red`

- &gd.value.red;

`green`

- &gd.value.green;

`blue`

- &gd.value.blue;

`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.
&reftitle.returnvalues;

A color identifier or &false; if the allocation failed.

&return.falseproblem;
&reftitle.changelog;

&Version; | &Description;
&gd.changelog.image-param;

&reftitle.examples;

### 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);
    ?>

&example.outputs.similar; Output of example : Example of using imagecolorallocatealpha()

### 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));
    ?>

&example.outputs;

    int(127)
    int(0)

&reftitle.seealso;

- `imagecolorallocate`
- `imagecolordeallocate`