Index: wp-includes/class-wp-image-editor-gd.php
===================================================================
--- wp-includes/class-wp-image-editor-gd.php	(revision 24312)
+++ wp-includes/class-wp-image-editor-gd.php	(working copy)
@@ -353,7 +353,9 @@
 			if ( function_exists('imageistruecolor') && ! imageistruecolor( $image ) )
 				imagetruecolortopalette( $image, false, imagecolorstotal( $image ) );
 
-			if ( ! $this->make_image( $filename, 'imagepng', array( $image, $filename ) ) )
+			$compression = - ( ( 0.09 * $this->quality ) - 9 ); // from 0 (no compression) to 9.
+			
+			if ( ! $this->make_image( $filename, 'imagepng', array( $image, $filename, $compression ) ) )
 				return new WP_Error( 'image_save_error', __('Image Editor Save Failed') );
 		}
 		elseif ( 'image/jpeg' == $mime_type ) {