Floresense Resource center: PHP Imaging support & Image manipulation

About / Contact Home

Support Desk Resource Center Products/Services

PHP Imaging support & Image manipulation - An overview of possibilities

Posted by: Floresense Team

Pages: 1 2 3 4

Colors:

Like in any drawing application one will need to create a color object or pen before drawing in a particular color, PHP also has the function imagecolorallocate() to create a color object.

$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);
// hexadecimal way
$white = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
$black = imagecolorallocate($im, 0x00, 0x00, 0x00);

where $im is the image resource on which we are going to use the color.

Color Alpha / transparency:

We use the method imagecolorallocatealpha() to set a color as transparent, or to set the opacity of a layer of the image.

$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);

The last parameter of imagecolorallocatealpha '75' mentions the opacity level of the objects drawn with $yellow. For example a circle drawn over a photograph with $yellow as color, would show the photo through the circle.

Sample code that generated above image: (use any image file in place of celebration1.jpg)

<?php
//create image from jpg file
$im = imagecreatefromjpeg("Celebration1.jpg");
if ($im)
{
  // allocate colors with alpha values
  $yellow = imagecolorallocatealpha($im, 255, 255, 0, 55);
  // drawing circle over image
  $yellow_x = 60;  $yellow_y = 110;  $radius   = 100;
  imagefilledellipse($im, $yellow_x, $yellow_y, $radius, $radius, $yellow);
  // don't forget to output a correct header!
  header('Content-type: image/jpeg');
  // and finally, output the result
  imagejpeg($im);
  imagedestroy($im);
}
?>

In this sample we use the ellipse function with same width and height to draw a circle. Since this is possible, php doesnt have a separate method for drawing circles as of version v.3.x (new versions might have though they might internally only use the ellipse drawing code.. it doesnt matter).

Drawing:

In the above sample we used a drawing function, imagefilledellipse. Many more drawing methods are there.
imagearc
imageellipse
imageline
imagepolygon
imagerectangle, and so on..

For documentation on trying other image functions in php check http://www.php.net/manual/en/ref.image.php, or http://www.php.net/manual/en/ for the full english php documentation.

Image resizing:

Image resizing is done with help of imagecopyresized() method.

This method actually copies an image from a source to a destination object.

1: We load the source image from a file using imagecreatefrom... methods.
2: We create a new blank small size image using imagecreatetruecolor().

We use this instead of imagecreate(), because we lose the colors if we created destination image with imagecreate().

<?php
  //load image
  $src_im = imagecreatefromjpeg("reef.jpg");
  //get size
  $src_width = imagesx($src_im);
  $src_height = imagesy($src_im);
  //fix resize factor... to 30% of image size both width and height.
  $resize_factor = .3;
  $new_width = $src_width * $resize_factor;
  $new_height = $src_height * $resize_factor;
  //since we apply the same resize factor for both widht and height,
  // it ensures proportionate resize
  //create new blank image for holding resized image
  $thumb_im = imagecreatetruecolor($new_width,$new_height);
  //we use imagecreatetruecolor instead of imagecreate to preserve colors
  //during resize.
  // Resize
  imagecopyresized($thumb_im, $src_im, 0, 0, 0, 0,
                     $new_width, $new_height,
                     $src_width, $src_height);
  
  header('Content-type: image/jpeg');
  imagejpeg($thumb_im);
  imagedestroy($im);
?>

Interesting thing is, using the methods imagecopy and imagecopyresized we can resize even "any" rectangular portion of an image, and it need not be always the full image.

Pages: 1 2 3 4