Zebra_Image.php
private function _sharpen_image($image) {

        // if the "sharpen_images" is set to true and we're running an appropriate version of PHP
        // (the "imageconvolution" is available only for PHP 5.1.0+)
        if ($this->sharpen_images && version_compare(PHP_VERSION, '5.1.0') >= 0) {

            // the convolution matrix as an array of three arrays of three floats
            $matrix = array(
                array(-1.2, -1, -1.2),
                array(-1, 20, -1),
                array(-1.2, -1, -1.2),
            );

            // the divisor of the matrix
            $divisor = array_sum(array_map('array_sum', $matrix));

            // color offset
            $offset = 0;

            // sharpen image
            imageconvolution($image, $matrix, $divisor, $offset);

        }

        // return the image's identifier
        return $image;

    }
private function _sharpen_image($image) {

        // if the "sharpen_images" is set to true and we're running an appropriate version of PHP
        // (the "imageconvolution" is available only for PHP 5.1.0+)
        if ($this->sharpen_images && version_compare(PHP_VERSION, '5.1.0') >= 0) {

            // the convolution matrix as an array of three arrays of three floats
            $matrix = array(
                array(-1.2, -1, -1.2),
                array(-1, 20, -1),
                array(-1.2, -1, -1.2),
            );

            // the divisor of the matrix
            $divisor = array_sum(array_map('array_sum', $matrix));

            // color offset
            $offset = 0;

            // sharpen image
            imageconvolution($image, $matrix, $divisor, $offset);

        }

        // return the image's identifier
        return $image;

    }
private function _sharpen_image ( $ image ) { // if the "sharpen_images" is set to true and we're running an appropriate version of PHP
 // (the "imageconvolution" is available only for PHP 5.1.0+)
 if ( $ this -> sharpen_images && version_compare ( PHP_VERSION , '5.1.0' ) >= 0 ) { // the convolution matrix as an array of three arrays of three floats
 $ matrix = array ( array ( - 1.2 , - 1 , - 1.2 ) , array ( - 1 , 20 , - 1 ) , array ( - 1.2 , - 1 , - 1.2 ) , ) ; // the divisor of the matrix
 $ divisor = array_sum ( array_map ( 'array_sum' , $ matrix ) ) ; // color offset
 $ offset = 0 ; // sharpen image
 imageconvolution ( $ image , $ matrix , $ divisor , $ offset ) ; } // return the image's identifier
 return $ image ; }
Sharpens images. Useful when creating thumbnails.

Code taken from the comments at {@link http://docs.php.net/imageconvolution}.

<i>This function will yield a result only for PHP version 5.1.0+ and will leave the image unaltered for older
versions!</i>

@param  $identifier identifier  An image identifier

@access private
Sharpens images . Useful when creating thumbnails .