Custom image sharpening

Using the imageapi and imagecache 5.x-2.0 it is fairly easy to integrate new image filters.

Firstly, ensure that you have a custom module that you can edit, or create a new one using the two files given below:

File: extra_filters.info

; $Id:
name = Image unsharp mask
description = Misc. custom filters; including unsharp mask, ...
package = Other
version = 0.1

File: extra_filters.module

<?php

/**
 * Implementation of hook_imagecache_actions.
 *
 * @return array
 *   An array of information on the actions implemented by a module. The array contains a 
 *   sub-array for each action node type, with the machine-readable action name as the key. 
 *   Each sub-array has up to 3 attributes. Possible attributes:
 * 
 *     "name": the human-readable name of the action. Required.
 *     "description": a brief description of the action. Required.
 *     "file": the name of the include file the action can be found 
 *             in relative to the implementing module's path.
 */
function extra_filters_imagecache_actions() {
  $actions = array(
    'extra_filters_unsharp_mask' => array(
      'name' => 'Unsharp mask',
      'description' => 'Unsharp mask using amount, radius and threshold.',
      // using external files to reduce the server load and clutter in the module
      'file' => 'extra_filters_unsharp_mask.inc',
    ),
  );

  return $actions;
}
// don't add the ? > below to the real file
?>

Then define up the form fields and filter:

Go to http://vikjavev.no/computing/ump.php to get a copy of the UnsharpMask function and paste it into the following file.

File: extra_filters_unsharp_mask.inc

<?php
/**
 * Form to create the new filter parameters
 */
function extra_filters_unsharp_mask_form($action) {
  $form['amount'] = array(
    '#type' => 'textfield',
    '#title' => t('Amount'),
    '#default_value' => $action['amount'],
    '#description' => t('Amount to sharpen: (typically 50 - 200)'),
  );
  $form['radius'] = array(
    '#type' => 'textfield',
    '#title' => t('Radius'),
    '#default_value' => $action['radius'],
    '#description' => t('Radius: (typically 0.5 - 1)'),
  );
  $form['threshold'] = array(
    '#type' => 'textfield',
    '#title' => t('Threshold'),
    '#default_value' => $action['threshold'],
    '#description' => t('Threshold: (typically 0 - 5)'),
  );
  return $form;
}

/**
 * This lets the user see what parameters were selected for the action
 */
function theme_extra_filters_unsharp_mask($element) {
  $data = $element['#value'];
  return 'amount: '. $data['amount'] .', radius: '. $data['radius'] .', threshold: '. $data['threshold'];
}

/**
 * Prep the filter
 */
function extra_filters_unsharp_mask_image(&$image, $data) {
  $amount = $data['amount'] ? $data['amount'] : 100;
  $radius = $data['radius'] ? $data['radius'] : 0.75;
  $threshold = $data['threshold'] ? $data['threshold'] : 2.5;
  $image->res = UnsharpMask($image->res, $amount, $radius, $threshold);
  return true;
}

Paste the UnsharpMask function here.

// don't add the ? > below to the real file
?>

Now, enable the new module via the admin interface, and the new filter should be listed alongside the core filters.

If you can't see the new action in imagecache, clear the cache table or add a hook_enable (and also hook_disable) in the module with following simple line:

<?php
  cache_clear_all('imagecache_actions', 'cache');
?>

If you have any issues, use the forum topic http://drupal.org/node/281193 to discuss these.