What causes "Failed to imagecopyresampled() image: %s" in phacility/phabricator?

Raise PHP's memory_limit (php.ini / php-fpm pool) for web and daemon processes — GD needs several bytes per pixel for both buffers.

phacility/phabricator · error · Exception

Failed to imagecopyresampled() image: %s

Error message

Failed to imagecopyresampled() image: %s

What it means

The GD function imagecopyresampled() returned false while PhabricatorFileImageTransform was copying/rescaling pixels into the destination canvas; the collected PHP warnings (via PhutilErrorTrap) are appended to the message. GD returns false when the operation cannot be performed — most often memory exhaustion while allocating the resampled rows, or an invalid source/destination resource.

Source

Thrown at src/applications/files/transform/PhabricatorFileImageTransform.php:102

      return $this->applyImagemagick($argv);
    }

    $src = $this->getImage();
    $dst = $this->newEmptyImage($dst_w, $dst_h);

    $trap = new PhutilErrorTrap();
    $ok = @imagecopyresampled(
      $dst,
      $src,
      $off_x, $off_y,
      $src_x, $src_y,
      $cpy_w, $cpy_h,
      $src_w, $src_h);
    $errors = $trap->getErrorsAsString();
    $trap->destroy();

    if ($ok === false) {
      throw new Exception(
        pht(
          'Failed to imagecopyresampled() image: %s',
          $errors));
    }

    $data = PhabricatorImageTransformer::saveImageDataInAnyFormat(
      $dst,
      $this->file->getMimeType());

    return $this->newFileFromData($data);
  }

  protected function applyImagemagick(array $argv) {
    $tmp = new TempFile();
    Filesystem::writeFile($tmp, $this->getData());

    $out = new TempFile();

View on GitHub (pinned to 5720a38cfe)

Solutions

Raise PHP's memory_limit (php.ini / php-fpm pool) for web and daemon processes — GD needs several bytes per pixel for both buffers.
Verify the source file is a valid raster image (re-encode it or strip bogus metadata) and that its pixel count is under the 4096x4096 transform cap.
Catch the exception at the transform call site and fall back to serving/storing the original, untransformed file.

Example fix

// before
$transformed = $transform->execute($file);

// after
try {
  $transformed = $transform->execute($file);
} catch (Exception $ex) {
  phlog($ex);
  $transformed = $file; // degrade gracefully to the original
}

Defensive patterns

Strategy: try-catch

Try / catch

try {
  $transformed = $transform->execute($file);
} catch (Exception $ex) {
  phlog(pht('Transform failed for %s: %s', $file->getPHID(), $ex->getMessage()));
  $transformed = $file; // fall back to the original
}

Prevention

Pre-check byte size (16MB cap) and pixel count (4096x4096 cap) before transforming.
Set memory_limit generously (512M+) on hosts that transform user images.
Treat transforms as best-effort: always have an original-file fallback path.

When it happens

Trigger: Executing any built-in image transform (thumbnails, profile-crops, the transform pipeline in PhabricatorFileImageTransform::applyTransform) on a file whose decoded bitmap is large relative to PHP's memory_limit, so the resample of e.g. 4000x3000 into a thumb exhausts memory mid-copy.

Common situations: Default PHP memory_limit (128M) with multi-megapixel JPEGs; a transform applied to a file that passed getimagesize() but decodes into a huge bitmap; GD built without proper support; concurrent transforms on a memory-constrained host.

Related errors

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/99db143f0c89451f. Report an issue: GitHub.