PHP GD Functions

$image symbolized by a identifier returned by one of the image creation functions.

The red color value: 0 ≥ $red ≤ 255.

The green color value: 0 ≥ $green ≤ 255.

The blue color value: 0 ≥ $blue ≤ 255.

The alpha value: 0 ≥ $alpha ≤ 127, where 0 indicates completely opaque while 127 indicates completely transparent.

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.

This function may return the index of the specified color plus alpha in the palette of the image, or -1 if the color does not exist in the image's palette.


<?php

int imagecolorexactalpha ( 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

The 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

// RUN this code several times
 
echo 'PHP VERSION: ' . PHP_VERSION . '<br><br>';

// $lang = 'pt';
$lang = 'en';

$org_img = "png/PNG 035 01 Nathan Phillips Sq.png";

$imorgimg = imagecreatefrompng($org_img);
$nbr_c_o = imagecolorstotal($imorgimg);

if($nbr_c_o == 0)
{
$pt = '<br>IMAGEM TRUECOLOR ';
$en = '<br>TRUECOLOR IMAGE ';
}
else
{
$pt = ' IMAGEM PALETIZADA '. $nbr_c_o .' cores ';
$en = ' PALLETIZED IMAGE '. $nbr_c_o .' colors ';
}
?>
<?php echo $org_img; ?><br><?php echo $$lang; ?><br><br>
<img src="<?php echo $org_img; ?>"
 alt="<?php echo $org_img; ?>" 
 title="<?php echo $org_img; ?>" width="400"><br><br>
 
 <?php
 $pal_ndx = mt_rand(0, 526619192);
 $pal_org = "png/PNG 035 01 Nathan Phillips Sq-ndx.png";
 
$col_ndx = imagecolorsforindex($imorgimg, $pal_ndx);

$pt = 'Índice da Paleta = ';
$en = 'Palette Index = ';

echo $$lang . $pal_ndx
 . ' <br><br><pre>';

print_r($col_ndx);

echo '</pre>';

$red = $col_ndx['red'];
$green = $col_ndx['green'];
$blue = $col_ndx['blue'];
$alpha = $col_ndx['alpha'];

$impalorg = imagecreate(imagesx($imorgimg), 60);
imagecolorallocate($impalorg, $red, $green, $blue);
imagepng($impalorg, $pal_org);
?>

<br>
<?php echo $pal_org;

$pt = "Cor: ";
$en = "Color: ";

?>

<br><br><img src="<?php echo $pal_org; ?>" alt="<?php echo $pal_org; ?>" width="400" height="40"><br><br>
<?php
echo $$lang
 . ' RGB = ( ' . $red . ', ' . $green . ', ' . $blue . ' ) ';
 
 $exc_alpha = imagecolorexactalpha($imorgimg,
                                                $red, $green, $blue, $alpha);
 
 $pt = 'Índice da paleta<sub>ex</sub>: ' . $exc_alpha;
 $en = 'Palette index<sub>ex</sub>: ' . $exc_alpha;
 echo '<br><br>' . $$lang . ' ';

?>

RESULT

PNG 035 01 Nathan Phillips Sq.png

EXISTING TRUECOLOR IMAGE

Palette Index = 189473990

Array
(
[red] => 75
[green] => 36
[blue] => 198
[alpha] => 11
)

PNG 035 01 Nathan Phillips Sq-ndx.png

PNG 035 01 Nathan Phillips Sq-ndx.png apr

Color: RGB = ( 75, 36, 198 )

Palette index_ex: 189473990

This is a particular result given the use of the mt_rand function to designate the palette index.

Run multiple times to get different results.

EXERCISE


<?php
 
// RUN this code several times
 
echo 'PHP VERSION: ' . PHP_VERSION . '<br><br>';

// $lang = 'pt';
$lang = 'en';

$org_img02 = "gif/GIF 017 01 Nathan Phillips Sq.gif";

$id_orgimg02 = imagecreatefromgif($org_img02);
$nbr_c_o02 = imagecolorstotal($id_orgimg02);

if($nbr_c_o02 == 0)
{
$pt = '<br>IMAGEM TRUECOLOR ';
$en = '<br>TRUECOLOR IMAGE ';
}
else
{
$pt = '<br>IMAGEM PALETIZADA '. $nbr_c_o02 .' cores ';
$en = '<br>PALLETIZED IMAGE '. $nbr_c_o02 .' colors ';
}
?>
<?php echo $org_img02; ?> <?php echo $$lang; ?><br><br>
<img src="<?php echo $org_img02; ?>"
 alt="<?php echo $org_img02; ?>" 
 title="<?php echo $org_img02; ?>" width="400"><br><br>
 
 <?php
 $pal_ndx02 = mt_rand(0, 252);
 $pal_org02 = "gif/GIF 017 01 Nathan Phillips Sq-ndx.gif";
 
$col_ndx = imagecolorsforindex($id_orgimg02, $pal_ndx02);

$pt = 'Índice da Paleta = ';
$en = 'Palette Index = ';

echo $$lang . $pal_ndx02
 . ' <br><br><pre>';

print_r($col_ndx);

echo '</pre>';

$red02 = $col_ndx['red'];
$green02 = $col_ndx['green'];
$blue02 = $col_ndx['blue'];
$alpha02 = $col_ndx['alpha'];

$id_palorg02 = imagecreate(imagesx($id_orgimg02), 30);

imagecolorallocate($id_palorg02, $red02, $green02, $blue02);
                                
imagegif($id_palorg02, $pal_org02);
?>

<br>
<?php echo $pal_org02;

$pt = "Cor: ";
$en = "Color: ";

?>

<br><br><img src="<?php echo $pal_org02; ?>" alt="<?php echo $pal_org02; ?>" width="400" height="40"><br><br>
<?php
echo $$lang
 . ' RGB = ( ' . $red02 . ', ' . $green02 . ', ' . $blue02 . ' ) ';
 
 $exc_alpha02 = 
 imagecolorexactalpha($id_orgimg02, 
                                     $red02, $green02, $blue02, $alpha02);
 
 $pt = 'Índice da paleta<sub>ex</sub>: ' . $exc_alpha02;
 $en = 'Palette index<sub>ex</sub>: ' . $exc_alpha02;
 echo '<br><br>' . $$lang . ' ';

?>

RESULT

GIF 017 01 Nathan Phillips Sq.gif

EXISTING TRUECOLOR IMAGE

Palette Index = 104

Array
(
[red] => 181
[green] => 15
[blue] => 68
[alpha] => 0
)

GIF 017 01 Nathan Phillips Sq-ndx.gif

Color: RGB = ( 181, 15, 68 )

Palette index_ex: 104

This is a particular result given the use of the mt_rand function to designate the palette index.

Run multiple times to get different results.