PHP : How to create a shadow to an image using an alpha mask

Question

I have a PNG image with an alpha mask. I want to generate a shadow for this image, that would use the alpha mask.

a picture is worth thousand words http://www.brunet.fr/alpha.jpg

I suppose I would need to :

1. get the alpha mask from the first image
2. fill it with the appropriate color, and blur it
3. create a new blank white image
4. compose it with the shadow first, and the first image

But I can't found anywhere some tips, especially for the first part.

Edit : i found a begining of answer here I try it and let you know.

Thanks

Answer 1

At first , you need install the php ext named : Imagick

<?php 
/* Read the image into the object */ 
$im = new Imagick( 'a.png' ); 
$im->setImageFormat("png"); 

/* Make the image a little smaller, maintain aspect ratio */ 
$im->thumbnailImage( 200, null ); 

/* Clone the current object */ 
$shadow = $im->clone(); 

/* Set image background color to black 
        (this is the color of the shadow) */ 
$shadow->setImageBackgroundColor( new ImagickPixel( 'black' ) ); 

/* Create the shadow */ 
$shadow->shadowImage( 80, 3, 5, 5 ); 

/* Imagick::shadowImage only creates the shadow. 
        That is why the original image is composited over it */ 
$shadow->compositeImage( $im, Imagick::COMPOSITE_OVER, 0, 0 ); 

/* Display the image */ 
header( "Content-Type: image/png" ); 
echo $shadow;