<?php
/**
 * Copyright 2010-2017 Horde LLC (http://www.horde.org/)
 *
 * See the enclosed file LICENSE for license information (LGPL). If you
 * did not receive this file, see http://www.horde.org/licenses/lgpl21.
 *
 * @author    Michael J. Rubinsky <mrubinsk@horde.org>
 * @category  Horde
 * @license   http://www.horde.org/licenses/lgpl21 LGPL-2.1
 * @package   Image
 */

/**
 * Unsharp mask Image effect.
 *
 * @author    Michael J. Rubinsky <mrubinsk@horde.org>
 * @category  Horde
 * @copyright 2010-2017 Horde LLC
 * @license   http://www.horde.org/licenses/lgpl21 LGPL-2.1
 * @package   Image
 */
class Horde_Image_Effect_Im_Unsharpmask extends Horde_Image_Effect
{
    /**
     * Valid parameters:
     *   - radius: (float) Thickness of the sharpened edge. Should be greater
     *             than sigma (or 0, and imagick will attempt to auto choose).
     *             In general, radius should be roughly output dpi / 150.  So
     *             for display purposes a radius of 0.5 is suggested.
     *   - amount: (float) Amount of the difference between original and the
     *             blur image that gets added back to the original. Can be
     *             thought of as the "strength" of the effect. Too high may
     *             cause blocking of shadows and highlights. Given a decimal
     *             value indicating percentage, e.g. 1.2 = 120%
     *   - threshold: (float) Determines how large the brightness delta between
     *                adjacent pixels needs to be to sharpen the edge.  Larger
     *                values == less sharpening. Useful for preventing noisy
     *                images from being oversharpened.
     *
     * @var array
     */
    protected $_params = array(
        'radius' => 0.5,
        'amount' => 1,
        'threshold' => 0.05
    );

    /**
     * Applies the effect.
     */
    public function apply()
    {
        /* Calculate appropriate sigma:
         * Determines how the sharpening is graduated away from the center
         * pixel of the sharpened edge. In general, if radius < 1, then sigma =
         * radius else sigma = sqrt(radius) */
        $this->_params['sigma'] = ($this->_params['radius'] < 1)
            ? $this->_params['radius']
            : sqrt($this->_params['radius']);

        $this->_image->addPostSrcOperation(sprintf(
            '-unsharp %Fx%F+%F+%F',
            $this->_params['radius'], $this->_params['sigma'], $this->_params['amount'], $this->_params['threshold']
        ));
    }
}
