diff --git a/src/Canvas.php b/src/Canvas.php
index f72b30e..eacef13 100644
--- a/src/Canvas.php
+++ b/src/Canvas.php
@@ -26,17 +26,6 @@ class Canvas {
         }
     }
 
-    public function __destruct() {
-        $this->destroy();
-    }
-
-    public function destroy() : self
-    {
-        \is_resource($this->image) && \imagedestroy($this->image);
-
-        return $this;
-    }
-
     public function create(int $width, int $height) : self
     {
         $this->width = $width;
@@ -200,8 +189,18 @@ class Canvas {
         unset($src->image);
     }
 
-    public function constrain(int $width, int $height, bool $immutable = true) : self
+    public function constrain(? int $width, ? int $height, bool $immutable = true) : self
     {
+        if ($width === null && $height === null) {
+            throw new \LogicException("At least one limiting factor must be provided, either width or height (or both).");
+        }
+        elseif ($width === null) {
+            $width = $this->width * ( $height / $this->height );
+        }
+        elseif ($height === null) {
+            $height = $this->height * ( $width / $this->width );
+        }
+
         if ( ($this->width > $width) || ($this->height > $height) ) {
             if ($this->width > $this->height) {
                 $height = $this->height * ( $width / $this->width );
@@ -224,6 +223,7 @@ class Canvas {
             }
         }
 
+
         return $this;
     }
 
diff --git a/src/Image.php b/src/Image.php
index 3fe4e8e..46a21c3 100644
--- a/src/Image.php
+++ b/src/Image.php
@@ -120,12 +120,12 @@ class Image extends Canvas {
         return $img;
     }
 
-    public function save(int $quality = null, $filters = null) : bool
+    public function save(? int $quality = null, $filters = null) : bool
     {
         return $this->render($this->filename, $quality, $filters);
     }
 
-    public function render(string $path = null, int $quality = null, $filters = null) # : bool
+    public function render(? string $path = null, ? int $quality = null, $filters = null) # : bool
     {
         $layers = $this->layers();