PHP GD Functions

$image symbolized by a identifier returned by one of the image creation functions, such as imagecreatetruecolor.

This function sets the flag which determines whether to retain full alpha channel information, (as opposed to single-color transparency), when saving PNG images.

If $enable = FALSE the alpha-channel is not retained.

If $enable = TRUE the alpha-channel is retained.

This function returns TRUE on success or FALSE on failure.

ALPHA-CHANNEL

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

Basically interprets pixel-level transparency or opacity properties, including grayscale, especially for TRUECOLOR images in PNG format.


<?php

bool imagesavealpha(GdImage $image, bool $enable)

where,

$image = An image identifier

$enable = To decide if the alpha channel will be retained or not

?>

$image

The image identifier.

$enable

To decide if the alpha channel will be retained or not.

EXERCISE


<?php

echo 'PHP VERSION: ' . PHP_VERSION . '<br><br>';

$lang = 'en';

$org_img01 = "png/PNG 035 01 Nathan Phillips Sq.png";

$dst_img01a = "png/PNG 035 01 Nathan Phillips Sq no alpaha.png";

$dst_img01b = "png/PNG 035 01 Nathan Phillips Sq alpha.png";

$id_org_img01 = imagecreatefrompng($org_img01);
$nbr_colors_org_img01 = imagecolorstotal($id_org_img01);

if($nbr_colors_org_img01 == 0)
{
$en = '<br>TRUECOLOR IMAGE';
}
else
{
$en = 'PALLETIZED IMAGE '. $nbr_colors_org_img01 .' colors';
}

echo $org_img01; ?><?php echo $$lang; ?><br><br>
<img src="<?php echo $org_img01; ?>"
 alt="<?php echo $org_img01; ?>" 
 title="<?php echo $org_img01; ?>" width="400"><br><br> 
 
<?php

$id_org_img01 = imagecreatefrompng($org_img01);

$save_flag01 = 0;

$save_alpha01 = imagesavealpha ($id_org_img01, $save_flag01);
imagepng($id_org_img01, $dst_img01a);

echo $dst_img01a; ?> <?php echo '<br>save flag = ' . 
$save_flag01; ?><br><br>
<img src="<?php echo $dst_img01a; ?>"
 alt="<?php echo $dst_img01a; ?>" 
 title="<?php echo $dst_img01a; ?>" width="400"><br><br>
  
 <?php

$id_org_img02 = imagecreatefrompng($org_img01);

$save_flag02 = 1;

$save_alpha02 = imagesavealpha ($id_org_img02, $save_flag02);
imagepng($id_org_img02, $dst_img01b);

echo $dst_img01b; ?> <?php echo '<br>save flag = ' . 
$save_flag02; ?><br><br>
<img src="<?php echo $dst_img01b; ?>"
 alt="<?php echo $dst_img01b; ?>" 
 title="<?php echo $dst_img01b; ?>" width="400"><br>

RESULT

PNG 035 01 Nathan Phillips Sq.png

TRUECOLOR IMAGE

PNG 035 01 Nathan Phillips Sq no alpaha.png

save flag = 0
ALPHA-CHANNEL IS NOT RETAINED

PNG 035 01 Nathan Phillips Sq no alpaha.png apr

PNG 035 01 Nathan Phillips Sq alpha.png

save flag = 1
ALPHA-CHANNEL IS RETAINED

PNG 035 01 Nathan Phillips Sq alpha.png apr

EXERCISE


<?php

echo 'PHP VERSION: ' . PHP_VERSION . '<br><br>';

$lang = 'en';

$org_img02 = "png/PNG 036 02 pomegranate.png";

$dst_img02a = "png/PNG 036 02 pomegranate no alpaha.png";

$dst_img02b = "png/PNG 036 02 pomegranate alpaha.png";

$id_org_img02 = imagecreatefrompng($org_img02);
$nbr_colors_org_img02 = imagecolorstotal($id_org_img02);

if($nbr_colors_org_img02 == 0)
{
$en = '<br>TRUECOLOR IMAGE';
}
else
{
$en = 'PALLETIZED IMAGE '. $nbr_colors_org_img02 .' 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

$id_org_img02 = imagecreatefrompng($org_img02);

$save_flag02 = 0;

$save_alpha02 = imagesavealpha ($id_org_img02, $save_flag02);
imagepng($id_org_img02, $dst_img02a);

echo $dst_img02a; ?> <?php echo '<br>save flag = ' . 
$save_flag02; ?><br><br>
<img src="<?php echo $dst_img02a; ?>"
 alt="<?php echo $dst_img02a; ?>" 
 title="<?php echo $dst_img02a; ?>" width="400"><br><br>
  
 <?php

$id_org_img03 = imagecreatefrompng($org_img02);

$save_flag03 = 1;

$save_alpha03 = imagesavealpha ($id_org_img03, $save_flag03);
imagepng($id_org_img03, $dst_img02b);

echo $dst_img02b; ?> <?php echo '<br>save flag = ' . 
$save_flag03; ?><br><br>
<img src="<?php echo $dst_img02b; ?>"
 alt="<?php echo $dst_img02b; ?>" 
 title="<?php echo $dst_img02b; ?>" width="400"><br>

RESULT

PNG 036 02 pomegranate.png

TRUECOLOR IMAGE

PNG 036 02 pomegranate.png apr

PNG 036 02 pomegranate no alpaha.png

save flag = 0
ALPHA-CHANNEL IS NOT RETAINED

PNG 036 02 pomegranate no alpaha.png apr

056 01 PNG 036 02 pomegranate alpaha.png

save flag = 1
ALPHA-CHANNEL IS RETAINED

EXERCISE


<?php

echo 'PHP VERSION: ' . PHP_VERSION . '<br><br>';

$lang = 'en';

$org_img03 = "gif/GIF 016 03 flowers.gif";

$dst_img03a = "gif/GIF 016 03 flowers no alpha.gif";

$dst_img03b = "gif/GIF 016 03 flowers alpha.gif";

$id_org_img03 = imagecreatefromgif($org_img03);
$nbr_colors_org_img03 = imagecolorstotal($id_org_img03);

if($nbr_colors_org_img03 == 0)
{
$en = '<br>TRUECOLOR IMAGE';
}
else
{
$en = '<br>PALLETIZED IMAGE<br>'. 
$nbr_colors_org_img03 .' colors';
}
?> 

<?php echo $org_img03; ?><?php echo $$lang; ?><br><br>
<img src="<?php echo $org_img03; ?>"
 alt="<?php echo $org_img03; ?>" 
 title="<?php echo $org_img03; ?>"><br><br> 
 
<?php

$id_org_img03 = imagecreatefromgif($org_img03);

$save_flag03 = 0;

$save_alpha03 = imagesavealpha ($id_org_img03, 
                                                       $save_flag03);
imagegif($id_org_img03, $dst_img03a);

echo $dst_img03a; ?> 
<?php echo '<br>save flag = ' . $save_flag03; ?><br><br>
<img src="<?php echo $dst_img03a; ?>"
 alt="<?php echo $dst_img03a; ?>" 
 title="<?php echo $dst_img03a; ?>"><br><br>
  
 <?php

$id_org_img04 = imagecreatefromgif($org_img03);

$save_flag04 = 1;

$save_alpha04 = imagesavealpha ($id_org_img04, 
                                                       $save_flag04);
imagegif($id_org_img04, $dst_img03b);

echo $dst_img03b; ?> 
<?php echo '<br>save flag = ' . $save_flag04; ?><br><br>
<img src="<?php echo $dst_img03b; ?>"
 alt="<?php echo $dst_img03b; ?>" 
 title="<?php echo $dst_img03b; ?>"><br>