Drupal 7 failed to open stream: Permission denied in image_gd_save() - php

Question

I am trying to generate and scaled image for thumbnails, scaling image has no problem and when use
image_save($_image) // Works Fine
(using the same folder an replacing) this code has not problem, the problem starts when I tried to save images in another destination folder using destination parameter:
image_save($_image, $destination) //throws errors
then the error occurs:
Warning: imagejpeg(C:\xampp\htdocs\drupal-devel\sites\default\files): failed to open stream: Permission denied in image_gd_save() (line 284 of C:\xampp\htdocs\drupal-devel\modules\system\image.gd.inc).
I'm working into a Windows xampp and using the function is_write of PHP, return true, no problem with permissions.
I had been trying for a time and I don't know what's happening, no problem with permissions.
This is my code:
$destination = 'public://gallery/thumbs/';
$filepath = drupal_get_path('module', 'gallery_blueprint') . '/img/large/1.jpg'
// Someplace before function
file_prepare_directory($destination, FILE_CREATE_DIRECTORY);
_generate_thumb($filepath,$destionation,300,NULL);
// Function code
function _generate_thumb($filepath, $destination_path, $width = NULL, $height = NULL) {
$_img = image_load($filepath);
$scaled = image_scale($_img, $width, $height); // Return true
$result = image_save($_img, $destination_path); //Error occurs whit destination path
return $result;
}

Answer 1

Is an stupid answer but will be written.
the function image_save() when you pass throw the $destination folder, it doesn't write the name by default, finally you need to write a final absolute name path, the name of file is required or throws.
Warning: imagejpeg(C:\xampp\htdocs\drupal-devel\sites\default\files): failed to open stream: Permission denied in image_gd_save() (line 284 of C:\xampp\htdocs\drupal-devel\modules\system\image.gd.inc).
//finally you need to write whole filepath
image_save($_img, $finalname_path) //$filname_path = public://gallery/thumbs/1.jpg