If you have a very large image file, or a high-resolution image, it's possible that Imagick fails to read that file.
Lets say your server has 512MB of memory and you try to generate a thumbnail image from a 300DPI image with a resolution of 15000 x 15000 pixels and thus also a large filesize.
What happens is, when Drupal tries to create an image style from that image, it fails and you see this in your log messages:
Unable to generate the derived image located at ....
Yes that's good, but you have no idea WHY drupal was unable to generate the derived image.
I figured out that the source is this piece of code in ImagickToolkit.php:
public function parseFile() {
$success = FALSE;
try {
$resource = new Imagick();
$resource->setBackgroundColor(new ImagickPixel('transparent'));
$resource->readImage($this->getPath());
$this->setResource($resource);
$success = TRUE;
} catch (ImagickException $e) {}
// cleanup local file if the original was remote
if ($this->isRemoteUri($this->getPath())) {
$this->fileSystem->delete($this->getPath());
}
return $success;
}
There are 2 things wrong here I think:
- There is no logging in the catch() part so you never know exactly what went wrong
- It is possible that the $resource (Imagick) object is halfway created before something fails and its never cleared.
I suggest adapting this piece of code to:
public function parseFile() {
$success = FALSE;
$resource = new Imagick();
try {
$resource->setBackgroundColor(new ImagickPixel('transparent'));
$resource->readImage($this->getPath());
$this->setResource($resource);
$success = TRUE;
} catch (ImagickException $e) {
$resource->clear();
$this->logger->error('Failed parsing file %file: %message', ['%file' => $this->getPath(),'%message' => $e->getMessage()]);
}
// cleanup local file if the original was remote
if ($this->isRemoteUri($this->getPath())) {
$this->fileSystem->delete($this->getPath());
}
return $success;
}
That would fix both problems and would generate a helpful watchdog message like this:
Failed parsing file /data/sites/web/mywebsitecom/production/private/assets/images/myverylargeimage.jpg: CacheResourcesExhausted `/data/sites/web/mywebsitecom/production/private/assets/images/myverylargeimage.jpg' @ error/cache.c/OpenPixelCache/4095
Now for those who care they can at least know that Drupal failed to generate the derived image because of Imagick CacheResourcesExhausted