diff --git a/system/src/Grav/Common/Page/Media.php b/system/src/Grav/Common/Page/Media.php
index c8385ea15..c4451e08c 100644
--- a/system/src/Grav/Common/Page/Media.php
+++ b/system/src/Grav/Common/Page/Media.php
@@ -74,16 +74,13 @@ class Media extends Getters
             }
 
             // Create the base medium
-            if (!empty($types['base'])) {
+            if (empty($types['base'])) {
+                $max = max(array_keys($types['alternative']));
+                $medium = $types['alternative'][$max]['file'];
+                $medium = MediumFactory::scaledFromMedium($medium, $max, 1)['file'];
+            } else {
                 $medium = MediumFactory::fromFile($types['base']['file']);
                 $medium && $medium->set('size', $types['base']['size']);
-            } else if (!empty($types['alternative'])) {
-                $altMedium = reset($types['alternative']);
-                $ratio = key($types['alternative']);
-
-                $altMedium = $altMedium['file'];
-
-                $medium = MediumFactory::scaledFromMedium($altMedium, $ratio, 1)['file'];
             }
 
             if (empty($medium)) {
@@ -103,10 +100,9 @@ class Media extends Getters
             // Build missing alternatives
             if (!empty($types['alternative'])) {
                 $alternatives = $types['alternative'];
-
                 $max = max(array_keys($alternatives));
 
-                for ($i=2; $i < $max; $i++) {
+                for ($i=$max; $i > 1; $i--) {
                     if (isset($alternatives[$i])) {
                         continue;
                     }
@@ -115,7 +111,9 @@ class Media extends Getters
                 }
 
                 foreach ($types['alternative'] as $ratio => $altMedium) {
-                    $medium->addAlternative($ratio, $altMedium['file']);
+                    if ($altMedium['file'] != $medium) {
+                        $medium->addAlternative($ratio, $altMedium['file']);
+                    }
                 }
             }
 
diff --git a/system/src/Grav/Common/Page/Medium/ImageMedium.php b/system/src/Grav/Common/Page/Medium/ImageMedium.php
index e3900baef..a2bb7b169 100644
--- a/system/src/Grav/Common/Page/Medium/ImageMedium.php
+++ b/system/src/Grav/Common/Page/Medium/ImageMedium.php
@@ -65,11 +65,6 @@ class ImageMedium extends Medium
         'zoomCrop' => [0, 1]
     ];
 
-    /**
-     * @var array
-     */
-    protected $derivatives = [];
-
     /**
      * @var string
      */
@@ -197,27 +192,19 @@ class ImageMedium extends Medium
      */
     public function srcset($reset = true)
     {
-        if (empty($this->alternatives) && empty($this->derivatives)) {
+        if (empty($this->alternatives)) {
             if ($reset) {
                 $this->reset();
             }
+
             return '';
         }
 
-        if (!empty($this->derivatives)) {
-            asort($this->derivatives);
-
-            foreach ($this->derivatives as $url => $width) {
-                $srcset[] = $url . ' ' . $width . 'w';
-            }
-
-            $srcset[] = $this->url($reset) . ' ' . $this->get('width') . 'w';
-        } else {
-            $srcset = [$this->url($reset) . ' ' . $this->get('width') . 'w'];
-            foreach ($this->alternatives as $ratio => $medium) {
-                $srcset[] = $medium->url($reset) . ' ' . $medium->get('width') . 'w';
-            }
+        $srcset = [];
+        foreach ($this->alternatives as $ratio => $medium) {
+            $srcset[] = $medium->url($reset) . ' ' . $medium->get('width') . 'w';
         }
+        $srcset[] = $this->url($reset) . ' ' . $this->get('width') . 'w';
 
         return implode(', ', $srcset);
     }
@@ -257,31 +244,53 @@ class ImageMedium extends Medium
      * @return $this
      */
     public function derivatives($min_width, $max_width, $step = 200) {
-      $width = $min_width;
-
-      // Do not upscale images.
-      if ($max_width > $this->get('width')) {
-        $max_width = $this->get('width');
-      }
-
-      while ($width <= $max_width) {
-        $ratio = $width / $this->get('width');
-        $derivative = MediumFactory::scaledFromMedium($this, 1, $ratio);
-        if (is_array($derivative)) {
-          $this->addDerivative($derivative['file']);
+        if (!empty($this->alternatives)) {
+            $max = max(array_keys($this->alternatives));
+            $base = $this->alternatives[$max];
+        } else {
+            $base = $this;
         }
-        $width += $step;
-      }
-      return $this;
-    }
 
-    /**
-     * Add a derivative
-     *
-     * @param  ImageMedium $image
-     */
-    public function addDerivative(ImageMedium $image) {
-      $this->derivatives[$image->url()] = $image->get('width');
+        // Do not upscale images.
+        $max_width = min($max_width, $base->get('width'));
+
+        for ($width = $min_width; $width < $max_width; $width = $width + $step) {
+            // Only generate image alternatives that don't already exist
+            if (array_key_exists((int) $width, $this->alternatives)) {
+                continue;
+            }
+
+            $derivative = MediumFactory::fromFile($base->get('filepath'));
+
+            // It's possible that MediumFactory::fromFile returns null if the
+            // original image file no longer exists and this class instance was
+            // retrieved from the page cache
+            if (isset($derivative)) {
+                $index = 2;
+                $widths = array_keys($this->alternatives);
+                sort($widths);
+
+                foreach ($widths as $i => $key) {
+                    if ($width > $key) {
+                        $index += max($i, 1);
+                    }
+                }
+
+                $basename = preg_replace('/(@\d+x){0,1}$/', "@{$width}w", $base->get('basename'), 1);
+                $derivative->setImagePrettyName($basename);
+
+                $ratio = $base->get('width') / $width;
+                $height = $derivative->get('height') / $ratio;
+
+                $derivative->resize($width, $height);
+                $derivative->set('width', $width);
+                $derivative->set('height', $height);
+
+                $this->addAlternative($ratio, $derivative);
+            }
+        }
+
+        return $this;
     }
 
     /**
@@ -489,6 +498,10 @@ class ImageMedium extends Medium
             call_user_func_array([$this->image, $method], $args);
 
             foreach ($this->alternatives as $ratio => $medium) {
+                if (!$medium->image) {
+                    $medium->image();
+                }
+
                 $args_copy = $args;
 
                 // regular image: resize 400x400 -> 200x200
diff --git a/system/src/Grav/Common/Page/Medium/Medium.php b/system/src/Grav/Common/Page/Medium/Medium.php
index b13306f52..b9e338854 100644
--- a/system/src/Grav/Common/Page/Medium/Medium.php
+++ b/system/src/Grav/Common/Page/Medium/Medium.php
@@ -100,7 +100,9 @@ class Medium extends Data implements RenderableInterface
         }
 
         $alternative->set('ratio', $ratio);
-        $this->alternatives[(float) $ratio] = $alternative;
+        $width = $alternative->get('width');
+
+        $this->alternatives[$width] = $alternative;
     }
 
     /**
diff --git a/system/src/Grav/Common/Page/Medium/MediumFactory.php b/system/src/Grav/Common/Page/Medium/MediumFactory.php
index c75044f5c..3743a81cf 100644
--- a/system/src/Grav/Common/Page/Medium/MediumFactory.php
+++ b/system/src/Grav/Common/Page/Medium/MediumFactory.php
@@ -119,8 +119,8 @@ class MediumFactory
         }
 
         $ratio = $to / $from;
-        $width = (int) ($medium->get('width') * $ratio);
-        $height = (int) ($medium->get('height') * $ratio);
+        $width = $medium->get('width') * $ratio;
+        $height = $medium->get('height') * $ratio;
 
         $prev_basename = $medium->get('basename');
         $basename = str_replace('@'.$from.'x', '@'.$to.'x', $prev_basename);