Neos\Media\Domain\Model\ThumbnailGenerator\DocumentThumbnailGenerator::refresh PHP Method

    public function refresh(Thumbnail $thumbnail)
    {
        try {
            $filenameWithoutExtension = pathinfo($thumbnail->getOriginalAsset()->getResource()->getFilename(), PATHINFO_FILENAME);
            $temporaryLocalCopyFilename = $thumbnail->getOriginalAsset()->getResource()->createTemporaryLocalCopy();
            $documentFile = sprintf(in_array($thumbnail->getOriginalAsset()->getResource()->getFileExtension(), $this->getOption('paginableDocuments')) ? '%s[0]' : '%s', $temporaryLocalCopyFilename);
            $width = $thumbnail->getConfigurationValue('width') ?: $thumbnail->getConfigurationValue('maximumWidth');
            $height = $thumbnail->getConfigurationValue('height') ?: $thumbnail->getConfigurationValue('maximumHeight');
            $im = new \Imagick();
            $im->setResolution($this->getOption('resolution'), $this->getOption('resolution'));
            $im->readImage($documentFile);
            $im->setImageFormat('png');
            $im->setImageBackgroundColor('white');
            $im->setImageCompose(\Imagick::COMPOSITE_OVER);
            if (defined('\\Imagick::ALPHACHANNEL_OFF')) {
                // ImageMagick >= 7.0, Imagick >= 3.4.3RC1
                // @see https://pecl.php.net/package/imagick/3.4.3RC1
                $im->setImageAlphaChannel(\Imagick::ALPHACHANNEL_OFF);
            } else {
                $im->setImageAlphaChannel(\Imagick::ALPHACHANNEL_RESET);
            }
            $im->thumbnailImage($width, $height, true);
            if (method_exists($im, 'mergeImageLayers')) {
                // Replace flattenImages in imagick 3.3.0
                // @see https://pecl.php.net/package/imagick/3.3.0RC2
                $im->mergeImageLayers(\Imagick::LAYERMETHOD_MERGE);
            } else {
                $im->flattenImages();
            }
            $resource = $this->resourceManager->importResourceFromContent($im->getImageBlob(), $filenameWithoutExtension . '.png');
            $im->destroy();
            $thumbnail->setResource($resource);
            $thumbnail->setWidth($width);
            $thumbnail->setHeight($height);
        } catch (\Exception $exception) {
            $filename = $thumbnail->getOriginalAsset()->getResource()->getFilename();
            $sha1 = $thumbnail->getOriginalAsset()->getResource()->getSha1();
            $message = sprintf('Unable to generate thumbnail for the given document (filename: %s, SHA1: %s)', $filename, $sha1);
            throw new Exception\NoThumbnailAvailableException($message, 1433109652, $exception);
        }
    }