PHP GD Functions

This function ALLOCATE a particular color for an image with a transparency in $image.

PALETTE IMAGE

is the designation term for images with a small number of colors.

For this type of image, a maximum of 256 colors are accepted.

TRUECOLOR IMAGE

is the designation term for images with a great number of colors.

For this type of image, a maximum of 16,777,216 colors are accepted.

This function may return FALSE if the allocation failed, but may also return a non-Boolean value which evaluates to FALSE.

We recommed to use the operator === or var_dump for testing the returned value of this function.

ALPHA CHANNEL

or simply ALPHA, can be considered as the fourth component associated with color.

Basically, it interprets the transparency or opacity properties at the pixel level, including grayscale, especially in TRUECOLOR images, especially in PNG format.

0 ≥ $red ≤ 255, 0 ≥ $green ≤ 255 & 0 ≥ $blue ≤ 255

or

0x00 ≥ $red ≤ 0xff, 0x00 ≥ $green ≤ 0xff & 0x00 ≥ $blue ≤ 0xff

or

0x00 ≥ $red ≤ 0xFF, 0x00 ≥ $green ≤ 0xFF & 0x00 ≥ $blue ≤ 0xFF

0 ≥ $alpha ≤ 127

where 0 indicates completely opaque while 127 indicates completely transparent.


<?php

int|false imagecolorallocatealpha ( GdImage $image, 
                                                                  int $red, 
                                                                  int $green, 
                                                                  int $blue, 
                                                                  int $alpha )

where,

$image = An image identifier

$red = The value of red component of the color

$green = The value of green component of the color

$blue = The value of blue component of the color

$alpha = The value of alpha

?>

$image

An image identifier.

$red

The value of red component of the color .

$green

The value of green component of the color.

$blue

The value of blue component of the color.

$alpha

The value to determine the alpha to be applied to the color.

EXERCISE


<?php

$hi_alpha_img = 'png/PNG 007 01a.png';
$md_alpha_img = 'png/PNG 007 01b.png';
$lw_alpha_img = 'png/PNG 007 01c.png';
$no_alpha_img = 'png/PNG 007 01d.png';
 
$hi_alpha = 120;
$md_alpha = 60;
$lw_alpha = 10;
$no_alpha = 0;

$hialpha = @imagecreate (100, 50);
$hi = imagecolorallocatealpha ( $hialpha, 
                                0, 0, 120, $hi_alpha  );
imagepng ($hialpha, $hi_alpha_img);

$mdalpha = @imagecreate (100, 50);
$md = imagecolorallocatealpha ( $mdalpha, 
                                0, 0, 120, $md_alpha  );
imagepng ($mdalpha, $md_alpha_img);

$lwalpha = @imagecreate (100, 50);
$lw = imagecolorallocatealpha ( $lwalpha, 
                                0, 0, 120, $lw_alpha  );
imagepng ($lwalpha, $lw_alpha_img);

$noalpha = @imagecreate (100, 50);
$no = imagecolorallocatealpha ( $noalpha, 
                                0, 0, 120, $no_alpha );
imagepng ($noalpha, $no_alpha_img);

?>
<?php echo 'ALPHA = ' . $hi_alpha; ?><br> 
<img src="<?php echo 
                        $hi_alpha_img; ?>" alt="hi"><br><br>

<?php echo 'ALPHA = ' . $md_alpha; ?><br>
<img src="<?php echo 
                        $md_alpha_img; ?>" alt="md"><br><br>

<?php echo 'ALPHA = ' . $lw_alpha; ?><br>
<img src="<?php echo 
                       $lw_alpha_img; ?>" alt="lw"><br><br>

<?php echo 'ALPHA = ' . $no_alpha; ?><br>
<img src="<?php echo 
                       $no_alpha_img; ?>" alt="no"><br>

RESULT

ALPHA = 120

alpha hi.png apr

ALPHA = 60

alpha md.png apr

ALPHA = 10

alpha lw.png apr

ALPHA = 0

EXERCISE


<?php

define('P2PNG', 'png/');

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    A way to create color gradient
    with images generated separately

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

for ( $i = 52; $i <= 120; $i++ )
{

$pic[$i] = @imagecreate (6, 28);
$bkg = imagecolorallocatealpha ( $pic[$i], 255, 0, 0, $i );

imagepng ($pic[$i], P2PNG .  $i . ".png");

echo '<img src=' . P2PNG . $i . ".png " ;
echo ' border="0" alt="pic" title="pic">';
}

?>