note 70082 deleted from function.imagecreatefromgif by didou
| From: | didou@php.net | Date: | Sat, 13 Jan 2007 20:47:23 +0000 |
| Subject: | note 70082 deleted from function.imagecreatefromgif by didou | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-121606@lists.php.net to get a copy of this message | ||
Note Submitter: moxley at moxleydata dot com
----
I wanted to find out if a GIF is Black & White or Color, but I didn't want to wait around
for imagecreatefromgif() to parse a 200k file (about 1 second) to get the color map, so I wrote this
function to get a list of all the colors in the GIF. Hope it is useful for you.
<?php
function getGIFColorMap($file)
{
$fp = fopen($file, 'r');
$buf = fread($fp, 1024);
fclose($fp);
// Calculate number of colors
// buf[10] is the color info byte
$color_byte = ord($buf[10]);
$has_color_map = ($color_byte >> 7) & 1;
$color_res = (($color_byte >> 4) & 7) + 1;
$bits_per_pixel = ($color_byte & 7) + 1;
if (!$has_color_map) return null;
// buf[13] is the beginning of the color map
$color_map_index = 13;
$map = array();
for ($i=0; $i <= $bits_per_pixel; $i++) {
$index = $color_map_index + $i*3;
$r = ord($buf[$index]);
$g = ord($buf[$index + 1]);
$b = ord($buf[$index + 2]);
$map[$i] = array($r, $g, $b);
}
return $map;
}
$colors = getGIFColorMap("big.gif");
foreach ($colors as $i=>$color) {
echo "color[$i]: (red=$color[0], blue=$color[1], green=$color[2])\n";
}
?>