diff --git a/Controller/ManagerController.php b/Controller/ManagerController.php
index e57712c..4882752 100644
--- a/Controller/ManagerController.php
+++ b/Controller/ManagerController.php
@@ -59,8 +59,10 @@ public function indexAction(Request $request, FileTypeService $fileTypeService):
         }
         $fileManager = $this->newFileManager($queryParameters);
 
-        // Folder search
-        $directoriesArbo = $this->retrieveSubDirectories($fileManager, $fileManager->getDirName(), \DIRECTORY_SEPARATOR, $fileManager->getBaseName());
+        // Folder search, walks the whole directory tree, so only when the tree is displayed
+        $directoriesArbo = $fileManager->getTree()
+            ? $this->retrieveSubDirectories($fileManager, $fileManager->getDirName(), \DIRECTORY_SEPARATOR, $fileManager->getBaseName())
+            : null;
 
         // File search
         $finderFiles = new Finder();
@@ -116,7 +118,7 @@ public function indexAction(Request $request, FileTypeService $fileTypeService):
         }
 
         if ('dimension' === $orderBy) {
-            usort($fileArray, function (File $a, File $b) {
+            usort($fileArray, static function (File $a, File $b) {
                 $aDimension = $a->getDimension();
                 $bDimension = $b->getDimension();
                 if ($aDimension && !$bDimension) {
@@ -147,7 +149,7 @@ public function indexAction(Request $request, FileTypeService $fileTypeService):
         if ($isJson) {
             $fileList = $this->renderView('@ArtgrisFileManager/views/_manager_view.html.twig', $parameters);
 
-            return new JsonResponse(['data' => $fileList, 'badge' => $finderFiles->count(), 'treeData' => $directoriesArbo]);
+            return new JsonResponse(['data' => $fileList, 'badge' => \count($fileArray), 'treeData' => $directoriesArbo]);
         }
         $parameters['treeData'] = json_encode($directoriesArbo);
 
@@ -213,7 +215,7 @@ public function renameFileAction(Request $request, string $fileName): RedirectRe
                 $fileManager = $this->newFileManager($queryParameters);
                 $newfilePath = $fileManager->getCurrentPath().\DIRECTORY_SEPARATOR.$newfileName;
                 $oldfilePath = realpath($fileManager->getCurrentPath().\DIRECTORY_SEPARATOR.$fileName);
-                if (0 !== mb_strpos($newfilePath, $fileManager->getCurrentPath())) {
+                if (!str_starts_with($newfilePath, $fileManager->getCurrentPath())) {
                     $this->addFlash('danger', $this->translator->trans('file.renamed.unauthorized'));
                 } else {
                     $fs = new Filesystem();
@@ -305,7 +307,7 @@ public function deleteAction(Request $request): RedirectResponse {
                 $is_delete = false;
                 foreach ($queryParameters['delete'] as $fileName) {
                     $filePath = realpath($fileManager->getCurrentPath().\DIRECTORY_SEPARATOR.$fileName);
-                    if (0 !== mb_strpos($filePath, $fileManager->getCurrentPath())) {
+                    if (!str_starts_with($filePath, $fileManager->getCurrentPath())) {
                         $this->addFlash('danger', 'file.deleted.danger');
                     } else {
                          try {
@@ -338,7 +340,7 @@ public function deleteAction(Request $request): RedirectResponse {
 
                 $this->dispatch(FileManagerEvents::POST_DELETE_FOLDER);
                 $queryParameters['route'] = \dirname($fileManager->getRoute());
-                if ($queryParameters['route'] == '/') {
+                if ($queryParameters['route'] === '/') {
                     unset($queryParameters['route']);
                 }
 
@@ -449,7 +451,7 @@ private function newFileManager(array $queryParameters): FileManager {
         return $this->fileManager;
     }
 
-    protected function dispatch(string $eventName, array $arguments = []) {
+    protected function dispatch(string $eventName, array $arguments = []): void {
         $arguments = array_replace([
             'filemanager' => $this->fileManager,
         ], $arguments);
diff --git a/Helpers/File.php b/Helpers/File.php
index 0ff8846..46cbc4c 100644
--- a/Helpers/File.php
+++ b/Helpers/File.php
@@ -3,27 +3,45 @@
 namespace Artgris\Bundle\FileManagerBundle\Helpers;
 
 use Artgris\Bundle\FileManagerBundle\Service\FileTypeService;
+use Symfony\Component\ErrorHandler\ErrorHandler;
 use Symfony\Component\Finder\SplFileInfo;
 use Symfony\Contracts\Translation\TranslatorInterface;
 
 class File
 {
-    private $preview;
+    public const IMAGE_EXTENSIONS = ['gif', 'png', 'jpg', 'jpeg', 'svg', 'webp'];
+
+    private ?array $preview = null;
+
+    private array|false|string|null $dimension = null;
 
     /**
      * File constructor.
      */
     public function __construct(private SplFileInfo $file,private TranslatorInterface $translator,private FileTypeService $fileTypeService,private FileManager $fileManager)
     {
-        $this->preview = $this->fileTypeService->preview($this->fileManager, $this->file);
     }
 
     /**
+     * Memoized: sorting by dimension calls this for every comparison.
+     *
      * @return array|false|string
      */
     public function getDimension(): bool|array|string {
-        return preg_match('/(gif|png|jpe?g|svg|webp)$/i', $this->file->getExtension()) ?
-            @getimagesize($this->file->getPathname()) : '';
+        return $this->dimension ??= $this->readDimension();
+    }
+
+    private function readDimension(): array|false|string {
+        if (!\in_array(strtolower($this->file->getExtension()), self::IMAGE_EXTENSIONS, true)) {
+            return '';
+        }
+
+        try {
+            // Turns the warning emitted for unreadable or corrupt images into an exception
+            return ErrorHandler::call('getimagesize', $this->file->getPathname());
+        } catch (\ErrorException) {
+            return false;
+        }
     }
 
     public function getHTMLDimension(): ?string {
@@ -68,7 +86,7 @@ public function getAttribut(): ?string {
     }
 
     public function isImage(): bool {
-        return \array_key_exists('image', $this->preview);
+        return \array_key_exists('image', $this->getPreview());
     }
 
     public function getFile(): SplFileInfo {
@@ -81,7 +99,8 @@ public function setFile(SplFileInfo $file) :void
     }
 
     public function getPreview(): array {
-        return $this->preview;
+        // Lazy: the preview renders a Twig template, so build it only for files that are displayed
+        return $this->preview ??= $this->fileTypeService->preview($this->fileManager, $this->file);
     }
 
     public function setPreview(array $preview) :void
diff --git a/Helpers/FileManager.php b/Helpers/FileManager.php
index 2c57e92..8d2a74a 100644
--- a/Helpers/FileManager.php
+++ b/Helpers/FileManager.php
@@ -45,7 +45,7 @@ public function getRegex(): string
 
         return match ($this->getType()) {
             'media' => '/\.(mp4|ogg|webm)$/i',
-            'image' => '/\.(gif|png|jpe?g|svg|webp)$/i',
+            'image' => '/\.('.implode('|', File::IMAGE_EXTENSIONS).')$/i',
             default => '/.+$/i',
         };
     }
diff --git a/Service/FileTypeService.php b/Service/FileTypeService.php
index b5a9948..26f384d 100644
--- a/Service/FileTypeService.php
+++ b/Service/FileTypeService.php
@@ -2,13 +2,14 @@
 
 namespace Artgris\Bundle\FileManagerBundle\Service;
 
+use Artgris\Bundle\FileManagerBundle\Helpers\File;
 use Artgris\Bundle\FileManagerBundle\Helpers\FileManager;
 use SplFileInfo;
 use Symfony\Component\Routing\RouterInterface;
 use Twig\Environment;
 
 class FileTypeService {
-    const IMAGE_SIZE = [
+    public const IMAGE_SIZE = [
         FileManager::VIEW_LIST => '22',
         FileManager::VIEW_THUMBNAIL => '100',
     ];
@@ -72,19 +73,17 @@ public function fileIcon(string $filePath,?string $extension = null, ?int $size
 
         $imageTemplate = null;
 
-        if (null === $extension) {
-            $filePathTmp = strtok($filePath, '?');
-            $extension = pathinfo($filePathTmp, PATHINFO_EXTENSION);
-        }
+        // Strip the query string before reading the extension, then match it case-insensitively
+        $extension = strtolower($extension ?? (new SplFileInfo(explode('?', $filePath)[0]))->getExtension());
         switch (true) {
             case $this->isYoutubeVideo($filePath):
-            case preg_match('/(mp4|ogg|webm|avi|wmv|mov)$/i', $extension):
+            case \in_array($extension, ['mp4', 'ogg', 'webm', 'avi', 'wmv', 'mov'], true):
                 $fa = 'far fa-file-video';
                 break;
-            case preg_match('/(mp3|wav)$/i', $extension):
+            case \in_array($extension, ['mp3', 'wav'], true):
                 $fa = 'far fa-file-audio';
                 break;
-            case preg_match('/(gif|png|jpe?g|svg|webp)$/i', $extension):
+            case \in_array($extension, File::IMAGE_EXTENSIONS, true):
 
                 $fileName = $filePath;
                 if ($cachebreaker) {
@@ -112,19 +111,19 @@ public function fileIcon(string $filePath,?string $extension = null, ?int $size
                     'html' => $html,
                     'image' => true,
                 ];
-            case preg_match('/(pdf)$/i', $extension):
+            case 'pdf' === $extension:
                 $fa = 'far fa-file-pdf';
                 break;
-            case preg_match('/(docx?)$/i', $extension):
+            case \in_array($extension, ['doc', 'docx'], true):
                 $fa = 'far fa-file-word';
                 break;
-            case preg_match('/(xlsx?|csv)$/i', $extension):
+            case \in_array($extension, ['xls', 'xlsx', 'csv'], true):
                 $fa = 'far fa-file-excel';
                 break;
-            case preg_match('/(pptx?)$/i', $extension):
+            case \in_array($extension, ['ppt', 'pptx'], true):
                 $fa = 'far fa-file-powerpoint';
                 break;
-            case preg_match('/(zip|rar|gz)$/i', $extension):
+            case \in_array($extension, ['zip', 'rar', 'gz', 'tgz'], true):
                 $fa = 'far fa-file-archive';
                 break;
             case filter_var($filePath, FILTER_VALIDATE_URL):
diff --git a/Tests/Controller/ManagerControllerTest.php b/Tests/Controller/ManagerControllerTest.php
index e4e9ab0..fed9324 100644
--- a/Tests/Controller/ManagerControllerTest.php
+++ b/Tests/Controller/ManagerControllerTest.php
@@ -104,4 +104,30 @@ public function testTableTr()
             $this->assertSame($file, $crawler->filter('.list-blk tbody tr')->eq($i)->attr('class'));
         }
     }
+
+    public function testJsonWithoutTreeSkipsTreeData()
+    {
+        $this->getBackendPage(['conf' => 'default', 'tree' => 0, 'json' => 1]);
+        $data = json_decode($this->client->getResponse()->getContent(), true);
+
+        $this->assertNull($data['treeData']);
+        // SubDir and text.txt
+        $this->assertSame(2, $data['badge']);
+    }
+
+    public function testJsonWithTreeHasTreeData()
+    {
+        $this->getBackendPage(['conf' => 'default', 'json' => 1]);
+        $data = json_decode($this->client->getResponse()->getContent(), true);
+
+        $this->assertNotEmpty($data['treeData']);
+        // tree mode lists files only
+        $this->assertSame(1, $data['badge']);
+    }
+
+    public function testOrderByDimension()
+    {
+        $this->getBackendPage(['conf' => 'default', 'orderby' => 'dimension']);
+        $this->assertSame(200, $this->client->getResponse()->getStatusCode());
+    }
 }
diff --git a/Tests/Helpers/FileTest.php b/Tests/Helpers/FileTest.php
new file mode 100644
index 0000000..524f2b0
--- /dev/null
+++ b/Tests/Helpers/FileTest.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace Artgris\Bundle\FileManagerBundle\Tests\Helpers;
+
+use Artgris\Bundle\FileManagerBundle\Helpers\File;
+use Artgris\Bundle\FileManagerBundle\Helpers\FileManager;
+use Artgris\Bundle\FileManagerBundle\Service\FileTypeService;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Finder\SplFileInfo;
+use Symfony\Contracts\Translation\TranslatorInterface;
+
+class FileTest extends TestCase
+{
+    private string $dir;
+
+    protected function setUp(): void
+    {
+        $this->dir = sys_get_temp_dir().'/artgris-file-test-'.uniqid();
+        mkdir($this->dir);
+    }
+
+    protected function tearDown(): void
+    {
+        array_map('unlink', glob($this->dir.'/*'));
+        rmdir($this->dir);
+    }
+
+    public function testDimensionOfImage()
+    {
+        // 1x1 transparent PNG
+        $file = $this->createFile('pixel.PNG', base64_decode('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII='));
+
+        $this->assertSame([1, 1], \array_slice($file->getDimension(), 0, 2));
+    }
+
+    public function testDimensionOfCorruptImageIsFalse()
+    {
+        $file = $this->createFile('broken.png', 'not an image');
+
+        $this->assertFalse($file->getDimension());
+    }
+
+    public function testDimensionOfNonImageIsEmpty()
+    {
+        $file = $this->createFile('text.txt', 'text');
+
+        $this->assertSame('', $file->getDimension());
+    }
+
+    public function testPreviewIsNotBuiltUntilNeeded()
+    {
+        $fileTypeService = $this->createMock(FileTypeService::class);
+        $fileTypeService->expects($this->never())->method('preview');
+
+        $this->createFile('text.txt', 'text', $fileTypeService)->getDimension();
+    }
+
+    public function testPreviewIsBuiltOnce()
+    {
+        $fileTypeService = $this->createMock(FileTypeService::class);
+        $fileTypeService->expects($this->once())->method('preview')->willReturn(['image' => true]);
+
+        $file = $this->createFile('text.txt', 'text', $fileTypeService);
+
+        $this->assertTrue($file->isImage());
+        $this->assertSame(['image' => true], $file->getPreview());
+        $this->assertSame(['image' => true], $file->getPreview());
+    }
+
+    private function createFile(string $name, string $content, ?FileTypeService $fileTypeService = null): File
+    {
+        file_put_contents($this->dir.'/'.$name, $content);
+
+        return new File(
+            new SplFileInfo($this->dir.'/'.$name, '', $name),
+            $this->createMock(TranslatorInterface::class),
+            $fileTypeService ?? $this->createMock(FileTypeService::class),
+            $this->createMock(FileManager::class),
+        );
+    }
+}