Reflection Media » PHP

Making darkness or brightness transparent

Cristian — Mon, 06 Jul 2009 10:28:08 +0000

Let’s say you have the picture of a flame and you want to change the background. In order to do that you first must make the background transparent. But how can you do that? You can do it by hand using a brush but it’s not quite the effect I was looking for. So I figured there must be a way to automatically adjust the transparency of each pixel depending on it’s darkness.

This gave me the chance to play around with PHP GD, and I must say I’m quite impressed. It seems to be a really powerful image processing tool. Here is the script I came up with, and here it is in action.

Before

After

Pretty neat, huh? Here’s the script so you can see it without having to download the zip file.

// $url: the URL of the image you want to be processed. It can also be a local filename.
// $type: 0 for brightness, anything else for darkness.
// $mode: 0 for theoretical mode, anything else for Photoshop mode.
 
function transparent($url, $type=1, $mode=1){
// Create the old image
$old_image = imagecreatefromstring(file_get_contents($url));
 
// Create the new image of the same size as the old one
list($x_size, $y_size) = getimagesize($url);
$new_image = imagecreatetruecolor($x_size, $y_size);
 
// Turn off alpha blending and set alpha flag for our new image
imagealphablending($new_image, false);
imagesavealpha($new_image, true);
 
// Do the following for each pixel
for($y=0; $y<$y_size; $y++){
	for($x=0; $x<$x_size; $x++){
		// get it's color
		$rgb = imagecolorat($old_image, $x, $y);
		// and get the R, G and B components of the color
		$old_color = imagecolorsforindex($old_image, $rgb);
		$r = $old_color['red'];
		$g = $old_color['green'];
		$b = $old_color['blue'];
 
		// Define brightness:
		if ($mode) $brightness = max($r, $g, $b); // photoshop mode OR
		else $brightness = (max($r, $g, $b) + min($r, $g, $b)) / 2; // theoretical mode
 
		// Define darkness:
		$darkness = (255 - $brightness);
 
		// Generate transparence:
		if($type) $alpha = $darkness / 2; // for darkness OR
		else $alpha = $brightness / 2; // for brightness
 
		// Define the new color, same as the old one, but with alpha transparency
		$new_color = imagecolorallocatealpha($new_image, $r, $g, $b, $alpha);
		// Set that color to the pixel in the new image
		imagesetpixel($new_image, $x, $y, $new_color);
	}
}
 
// Output image to browser
header('Content-Type: image/png');
imagepng($new_image);
 
// Destroy all images in the end
imagedestroy($old_image);
imagedestroy($new_image);
}

Update: There’s also a Photoshop plugin for doing something similar, but it costs 27 euros.

404 email alert

Cristian — Fri, 29 May 2009 09:44:26 +0000

Here is a little PHP code snippet to add to your 404 page, in order to get an email alert with all sorts of useful data, each time a 404 page is accessed.

if(isset($_SERVER['HTTP_REFERER'])) {
    $ref=$_SERVER['HTTP_REFERER'];
}
else{
	$ref='none';
}
 
$sitename='Reflection Media';
 
$recipient = 'mail@gmail.com';
$subject = 'New '.$sitename.' 404 accessed';
$mail_body = '
A new 404 page has been accessed:
 
The accessed URI was: '.$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'].'
The user's IP address: '.$_SERVER['REMOTE_ADDR'].'
The user's Internet browser: '.$_SERVER['HTTP_USER_AGENT'].'
The URI from where your user came: '.$ref.'
';
$header = 'From: '.$sitename.' 404 page rn';
 
mail($recipient, $subject, $mail_body, $header);

Fun with PHP

Cristian — Mon, 16 Feb 2009 10:09:51 +0000

OK. So we know that instead of using the database, regular files can be used. It’s quite ineffective, but it’s possible. This means that the database structure and the regular file structure are somehow interchangeable.

So… this would mean that the database can be used instead of regular files.

Now, this is the obvious use of the BLOB object, but it’s mainly used for media files. What I had in mind are actual web-pages, including PHP code, stored inside the database.

The first obstacle I bumped into was that you can’t echo PHP code. I mean, you can do it, but it’s useless. The web server won’t parse your PHP twice, so it just sends PHP code to your browser, which is dumb.

1 2	echo "< ?php echo 'hello world'; ?>"; // does not work

The first solution that came to mind was writing the code in a temporary file and right after that include it, in the very same script. I’d love to hear other solutions to this problem.

So, once I got this figured out, the rest was more or less a piece of cake.

All I had to do was:

Connect to the MySQL server, select the database and fetch the results;
Create a temporary file, write the database results there and then close it;
Include the temporary file right there, in the same script;
Delete the temporary file and close the MySQL connection.

The table I used is a very simple one:

1
2
3

CREATE TABLE IF NOT EXISTS `webpages` (
  `name` varchar(10000) default NULL,
  `content` varchar(10000) default NULL);

And here is the little script:

// a function I made for easily linking to other database web pages:
function dblink($name){
	echo 'http://'.$_SERVER['SERVER_NAME'].$_SERVER['SCRIPT_NAME'].'?name='.$name;
}
// function for including the text of a database web page:
function dbinclude($name){
	// getting the content of the web page from the database:
	$result = mysql_query("SELECT * FROM webpages WHERE name='$name'");
	$row = mysql_fetch_array($result);
	// creating a tempoeary file and writing the web page content to it:
	$handle = fopen("temp.php", "w");
	fwrite($handle, $row['content']);
	fclose($handle);
	// include the text of the temporary file:
	include('temp.php');
}
// get the name of the database web page I want to include:
$name=$_GET['name'];
if ($name=='') $name='home';
// connect to the database:
$con = mysql_connect("localhost","your_username","your_password");
mysql_select_db("your_database", $con);
// include the content of the database web page:
dbinclude($name);
// close the MySQL connection and delete the temporary file:
mysql_close($con);
unlink('temp.php');

It’s the only file a site needs. Everything else can be in the database. Of course, I do realize that the database too is made of files.

You can test it here and you can download the script and sql file from here.