diff --git a/README.md b/README.md
index 53f29d1..4f86b63 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,7 @@ Contrast         | Supports changing contrast settings of an image. Also support
 Convolution      | Allows to build custom image filters like blur, emboss, sharpen and others (see http://docs.gimp.org/en/plug-in-convmatrix.html). | X          | IM only             |
 ImageMagick arguments | Directly enter ImageMagick command line arguments.                                      |            | X                   |
 Interlace        | Used to specify the type of interlacing scheme for raw image formats.                        | X          | IM only             |
+Opacity          | Change overall image transparency level.                                                     | X          | IM only             |
 Set canvas       | Places the source image over a colored or a transparent background of a defined size.        | X          | IM only             |
 Set transparent color | Defines the color to be used for transparency in GIF images.                            | X          | IM only             |
 Sharpen          | Sharpens an image (using convolution).                                                       | X          | IM only             |
diff --git a/config/schema/image_effects.schema.yml b/config/schema/image_effects.schema.yml
index 8157985..2ad089e 100644
--- a/config/schema/image_effects.schema.yml
+++ b/config/schema/image_effects.schema.yml
@@ -166,6 +166,14 @@ image.effect.image_effects_imagemagick_arguments:
       type: string
       label: 'Height in px or %'
 
+image.effect.image_effects_opacity:
+  type: mapping
+  label: 'Adjust image transparency level'
+  mapping:
+    opacity:
+      type: integer
+      label: 'Opacity % of the source image'
+
 image.effect.image_effects_set_canvas:
   type: mapping
   label: 'Set canvas image effect'
diff --git a/image_effects.module b/image_effects.module
index 52ac175..271bfbd 100644
--- a/image_effects.module
+++ b/image_effects.module
@@ -43,6 +43,10 @@ function image_effects_theme() {
     'image_effects_imagemagick_arguments_summary' => [
       'variables' => ['data' => NULL, 'effect' => []],
     ],
+    // Opacity image effect - summary
+    'image_effects_opacity_summary' => [
+      'variables' => ['data' => NULL, 'effect' => []],
+    ],
     // Set canvas image effect - summary
     'image_effects_set_canvas_summary' => [
       'variables' => ['data' => NULL, 'effect' => []],
diff --git a/src/Plugin/ImageEffect/OpacityImageEffect.php b/src/Plugin/ImageEffect/OpacityImageEffect.php
new file mode 100644
index 0000000..463549b
--- /dev/null
+++ b/src/Plugin/ImageEffect/OpacityImageEffect.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace Drupal\image_effects\Plugin\ImageEffect;
+
+use Drupal\Core\Image\ImageInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\image\ConfigurableImageEffectBase;
+
+/**
+ * Adjust image transparency.
+ *
+ * @ImageEffect(
+ *   id = "image_effects_opacity",
+ *   label = @Translation("Opacity"),
+ *   description = @Translation("Change overall image transparency level. Applies only to image formats that support Alpha channel, like PNG.")
+ * )
+ */
+class OpacityImageEffect extends ConfigurableImageEffectBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'opacity' => 50,
+    ] + parent::defaultConfiguration();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSummary() {
+    return [
+      '#theme' => 'image_effects_opacity_summary',
+      '#data' => $this->configuration,
+    ] + parent::getSummary();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form['opacity'] = [
+      '#type' => 'number',
+      '#title' => $this->t('Opacity'),
+      '#field_suffix' => '%',
+      '#description' => $this->t('Opacity: 0 - 100'),
+      '#default_value' => $this->configuration['opacity'],
+      '#min' => 0,
+      '#max' => 100,
+      '#maxlength' => 3,
+      '#size' => 3
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    parent::submitConfigurationForm($form, $form_state);
+    $this->configuration['opacity'] = $form_state->getValue('opacity');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applyEffect(ImageInterface $image) {
+    return $image->apply('opacity', ['opacity' => $this->configuration['opacity']]);
+  }
+
+}
diff --git a/src/Plugin/ImageToolkit/Operation/OpacityTrait.php b/src/Plugin/ImageToolkit/Operation/OpacityTrait.php
new file mode 100644
index 0000000..9dfab0c
--- /dev/null
+++ b/src/Plugin/ImageToolkit/Operation/OpacityTrait.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace Drupal\image_effects\Plugin\ImageToolkit\Operation;
+
+/**
+ * Base trait for image_effects Opacity operations.
+ */
+trait OpacityTrait {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function arguments() {
+    return [
+      'opacity' => [
+        'description' => 'Opacity.',
+        'required' => FALSE,
+        'default' => 100,
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function validateArguments(array $arguments) {
+    // Ensure opacity is in the range 0-100.
+    if (!is_numeric($arguments['opacity']) || $arguments['opacity'] > 100 || $arguments['opacity'] < 0) {
+      throw new \InvalidArgumentException("Invalid opacity ('{$arguments['opacity']}') specified for the image 'opacity' operation");
+    }
+    return $arguments;
+  }
+
+}
diff --git a/src/Plugin/ImageToolkit/Operation/gd/GDOperationTrait.php b/src/Plugin/ImageToolkit/Operation/gd/GDOperationTrait.php
index 35f064a..fbb2f1a 100644
--- a/src/Plugin/ImageToolkit/Operation/gd/GDOperationTrait.php
+++ b/src/Plugin/ImageToolkit/Operation/gd/GDOperationTrait.php
@@ -221,4 +221,70 @@ protected function _imagettfbbox($size, $angle, $fontfile, $text) {
     }
   }
 
+  /**
+   * Change overall image transparency level.
+   *
+   * This method implements the algorithm described in
+   * http://php.net/manual/en/function.imagefilter.php#82162
+   *
+   * @param resource $img
+   *   Image resource id.
+   * @param int $pct
+   *   Opacity of the source image in percentage.
+   *
+   * @return bool
+   *   Returns TRUE on success or FALSE on failure.
+   *
+   * @see http://php.net/manual/en/function.imagefilter.php#82162
+   */
+  function filterOpacity($img, $pct) {
+    if (!isset($pct)) {
+      return false;
+    }
+    $pct /= 100;
+
+    // Get image width and height.
+    $w = imagesx($img);
+    $h = imagesy($img);
+
+    // Turn alpha blending off.
+    imagealphablending($img, FALSE);
+
+    // Find the most opaque pixel in the image (the one with the smallest alpha
+    // value).
+    $min_alpha = 127;
+    for ($x = 0; $x < $w; $x++) {
+      for ($y = 0; $y < $h; $y++) {
+        $alpha = (imagecolorat($img, $x, $y) >> 24) & 0xFF;
+        if ($alpha < $min_alpha) {
+          $min_alpha = $alpha;
+        }
+      }
+    }
+
+    // Loop through image pixels and modify alpha for each.
+    for ($x = 0; $x < $w; $x++) {
+      for ($y = 0; $y < $h; $y++) {
+        // Get current alpha value (represents the TANSPARENCY!).
+        $color_xy = imagecolorat($img, $x, $y);
+        $alpha = ($color_xy >> 24) & 0xFF;
+        // Calculate new alpha.
+        if ($min_alpha !== 127) {
+          $alpha = 127 + 127 * $pct * ($alpha - 127) / (127 - $min_alpha);
+        }
+        else {
+          $alpha += 127 * $pct;
+        }
+        // Get the color index with new alpha
+        $alpha_color_xy = imagecolorallocatealpha($img, ($color_xy >> 16) & 0xFF, ($color_xy >> 8) & 0xFF, $color_xy & 0xFF, $alpha);
+        // Set pixel with the new color + opacity.
+        if (!imagesetpixel($img, $x, $y, $alpha_color_xy)) {
+          return FALSE;
+        }
+      }
+    }
+
+    return TRUE;
+  }
+
 }
diff --git a/src/Plugin/ImageToolkit/Operation/gd/Opacity.php b/src/Plugin/ImageToolkit/Operation/gd/Opacity.php
new file mode 100644
index 0000000..9ccf605
--- /dev/null
+++ b/src/Plugin/ImageToolkit/Operation/gd/Opacity.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Drupal\image_effects\Plugin\ImageToolkit\Operation\gd;
+
+use Drupal\system\Plugin\ImageToolkit\Operation\gd\GDImageToolkitOperationBase;
+use Drupal\image_effects\Plugin\ImageToolkit\Operation\gd\GDOperationTrait;
+use Drupal\image_effects\Plugin\ImageToolkit\Operation\OpacityTrait;
+
+/**
+ * Defines GD Opacity operation.
+ *
+ * @ImageToolkitOperation(
+ *   id = "image_effects_gd_opacity",
+ *   toolkit = "gd",
+ *   operation = "opacity",
+ *   label = @Translation("Opacity"),
+ *   description = @Translation("Adjust image transparency.")
+ * )
+ */
+class Opacity extends GDImageToolkitOperationBase {
+
+  use GDOperationTrait;
+  use OpacityTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(array $arguments) {
+    if ($arguments['opacity'] < 100) {
+      return $this->filterOpacity($this->getToolkit()->getResource(), $arguments['opacity']);
+    }
+    return TRUE;
+  }
+
+}
diff --git a/src/Plugin/ImageToolkit/Operation/imagemagick/Opacity.php b/src/Plugin/ImageToolkit/Operation/imagemagick/Opacity.php
new file mode 100644
index 0000000..df577ca
--- /dev/null
+++ b/src/Plugin/ImageToolkit/Operation/imagemagick/Opacity.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace Drupal\image_effects\Plugin\ImageToolkit\Operation\imagemagick;
+
+use Drupal\imagemagick\Plugin\ImageToolkit\Operation\imagemagick\ImagemagickImageToolkitOperationBase;
+use Drupal\image_effects\Plugin\ImageToolkit\Operation\OpacityTrait;
+
+/**
+ * Defines ImageMagick Opacity operation.
+ *
+ * @ImageToolkitOperation(
+ *   id = "image_effects_imagemagick_opacity",
+ *   toolkit = "imagemagick",
+ *   operation = "opacity",
+ *   label = @Translation("Opacity"),
+ *   description = @Translation("Adjust image transparency.")
+ * )
+ */
+class Opacity extends ImagemagickImageToolkitOperationBase {
+
+  use OpacityTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(array $arguments) {
+    if ($this->getToolkit()->getPackage() === 'graphicsmagick') {
+      // GraphicsMagick does not support -alpha argument, return early.
+      // @todo implement a GraphicsMagick solution if possible.
+      return FALSE;
+    }
+
+    switch ($arguments['opacity']) {
+      case 100:
+        // Fully opaque, leave image as-is.
+        break;
+
+      case 0:
+        // Fully transparent, set full transparent for all pixels.
+        $this->getToolkit()->addArgument("-alpha set -channel Alpha -evaluate Set 0%");
+        break;
+
+      default:
+        // Divide existing alpha to the opacity needed. This preserves
+        // partially transparent images.
+        $divide = number_format((float) (100 / $arguments['opacity']), 4, '.', ',');
+        $this->getToolkit()->addArgument("-alpha set -channel Alpha -evaluate Divide {$divide}");
+        break;
+
+    }
+
+    return TRUE;
+  }
+
+}
diff --git a/src/Tests/ImageEffectsOpacityTest.php b/src/Tests/ImageEffectsOpacityTest.php
new file mode 100644
index 0000000..846bd5a
--- /dev/null
+++ b/src/Tests/ImageEffectsOpacityTest.php
@@ -0,0 +1,69 @@
+<?php
+
+namespace Drupal\image_effects\Tests;
+
+/**
+ * Opacity effect test.
+ *
+ * @group Image Effects
+ */
+class ImageEffectsOpacityTest extends ImageEffectsTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    // @todo This effect does not work on GraphicsMagick.
+    $this->imagemagickPackages['graphicsmagick'] = FALSE;
+  }
+
+  /**
+   * Opacity effect test.
+   */
+  public function testOpacityEffect() {
+    // Test operations on toolkits.
+    $this->executeTestOnToolkits([$this, 'doTestOpacityOperations']);
+  }
+
+  /**
+   * Opacity operations test.
+   */
+  public function doTestOpacityOperations() {
+    // Test on the PNG test image.
+    $original_uri = $this->getTestImageCopyUri('/files/image-test.png', 'simpletest');
+
+    // Test data.
+    $test_data = [
+      // No transparency change.
+      '100' => [$this->red, $this->green, $this->transparent, $this->blue],
+      // 50% transparency.
+      '50' => [[255, 0, 0, 63], [0, 255, 0, 63], $this->transparent, [0, 0, 255, 63]],
+      // 100% transparency.
+      '0' => [$this->transparent, $this->transparent, $this->transparent, $this->transparent],
+    ];
+
+    foreach ($test_data as $opacity => $colors) {
+      // Add Opacity effect to the test image style.
+      $effect = [
+        'id' => 'image_effects_opacity',
+        'data' => [
+          'opacity' => $opacity,
+        ],
+      ];
+      $uuid = $this->addEffectToTestStyle($effect);
+
+      // Check that ::applyEffect generates image with expected opacity.
+      $derivative_uri = $this->testImageStyle->buildUri($original_uri);
+      $this->testImageStyle->createDerivative($original_uri, $derivative_uri);
+      $image = $this->imageFactory->get($derivative_uri, 'gd');
+      $this->assertTrue($this->colorsAreEqual($colors[0], $this->getPixelColor($image, 0, 0)));
+      $this->assertTrue($this->colorsAreEqual($colors[1], $this->getPixelColor($image, 39, 0)));
+      $this->assertTrue($this->colorsAreEqual($colors[2], $this->getPixelColor($image, 0, 19)));
+      $this->assertTrue($this->colorsAreEqual($colors[3], $this->getPixelColor($image, 39, 19)));
+
+      // Remove effect.
+      $uuid = $this->removeEffectFromTestStyle($uuid);
+    }
+  }
+}
diff --git a/templates/image-effects-opacity-summary.html.twig b/templates/image-effects-opacity-summary.html.twig
new file mode 100644
index 0000000..0e05bcf
--- /dev/null
+++ b/templates/image-effects-opacity-summary.html.twig
@@ -0,0 +1,19 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a summary of an image opacity effect.
+ *
+ * Available variables:
+ * - data: The current configuration for this opacity effect, including:
+ *   - opacity: The opacity of the image.
+ * - effect: The effect information, including:
+ *   - id: The effect identifier.
+ *   - label: The effect name.
+ *   - description: The effect description.
+ *
+ * @ingroup themeable
+ */
+#}
+{% spaceless %}
+  {{ data.opacity|e }}%
+{% endspaceless %}