diff --git a/lungmask/mask.py b/lungmask/mask.py
index 90df7c2..73ea08e 100644
--- a/lungmask/mask.py
+++ b/lungmask/mask.py
@@ -50,9 +50,6 @@ def apply(
     else:
         directions = np.asarray([1, 0, 0, 0, 1, 0, 0, 0, 1])
 
-    if model is None:
-        model = get_model("unet", "R231")
-
     if force_cpu:
         device = torch.device("cpu")
     else:
@@ -62,7 +59,10 @@ def apply(
             logging.info("No GPU support available, will use CPU. Note, that this is significantly slower!")
             batch_size = 1
             device = torch.device("cpu")
-    model.to(device)
+
+    if model is None:
+        model = get_model("unet", "R231")
+        model.to(device)
 
     if not noHU:
         tvolslices, xnew_box = utils.preprocess(inimg_raw, resolution=[256, 256])
@@ -117,7 +117,7 @@ def apply(
     if len(directions) == 9:
         outmask = np.flip(outmask, np.where(directions[[0, 4, 8]][::-1] < 0)[0])
 
-    return outmask.astype(np.uint8)
+    return outmask
 
 
 def get_model(modeltype, modelname):
diff --git a/lungmask/utils.py b/lungmask/utils.py
index 2d36506..a319fb3 100644
--- a/lungmask/utils.py
+++ b/lungmask/utils.py
@@ -13,33 +13,32 @@
 import skimage.morphology
 from torch.utils.data import Dataset
 from tqdm import tqdm
+import pandas as pd
+
 
 ORDER2OCVINTER = {0: cv2.INTER_NEAREST, 1: cv2.INTER_LINEAR, 2: cv2.INTER_AREA, 3: cv2.INTER_CUBIC}
 
 
-def preprocess(img, label=None, resolution=[192, 192]):
-    imgmtx = np.copy(img)
-    lblsmtx = np.copy(label)
+def preprocess(
+    imgmtx: np.ndarray, resolution: list = [192, 192]
+) -> Tuple[np.ndarray, np.ndarray]:
+    """Preprocesses the image by clipping, cropping and resizing. Clipping at -1024 and 600 HU, cropping to the body
+
+    Args:
+        imgmtx (np.ndarray): Image to be preprocessed
+        resolution (list, optional): Target size after preprocessing. Defaults to [192, 192].
 
-    imgmtx[imgmtx < -1024] = -1024
-    imgmtx[imgmtx > 600] = 600
+    Returns:
+        Tuple[np.ndarray, np.ndarray]: Preprocessed image and the cropping bounding box
+    """
+    imgmtx = np.clip(imgmtx, -1024, 600)
     cip_xnew = []
     cip_box = []
-    cip_mask = []
-    for i in range(imgmtx.shape[0]):
-        if label is None:
-            (im, m, box) = crop_and_resize(imgmtx[i, :, :], width=resolution[0], height=resolution[1])
-        else:
-            (im, m, box) = crop_and_resize(
-                imgmtx[i, :, :], mask=lblsmtx[i, :, :], width=resolution[0], height=resolution[1]
-            )
-            cip_mask.append(m)
+    for imslice in imgmtx:
+        im, _, box = crop_and_resize(imslice, width=resolution[0], height=resolution[1])
         cip_xnew.append(im)
         cip_box.append(box)
-    if label is None:
-        return np.asarray(cip_xnew), cip_box
-    else:
-        return np.asarray(cip_xnew), cip_box, np.asarray(cip_mask)
+    return np.asarray(cip_xnew), cip_box
 
 
 def simple_bodymask(img):
@@ -210,6 +209,21 @@ def get_input_image(path):
     return input_image
 
 
+def speedup_numpy_unique(array: np.ndarray, return_counts: bool = False):
+    """
+    Alternative accelerated version of numpy.unique for integer-based arrays
+    """
+
+    if return_counts is True:
+        counts = np.bincount(array.ravel())
+        unique = np.where(counts != 0)[0]
+        counts = counts[counts != 0]
+        return unique, counts
+    else:
+        unique = np.sort(pd.unique(array.ravel()))
+        return unique
+
+
 def postrocessing(label_image, spare=[], verbose=True):
     """some post-processing mapping small label patches to the neighbout whith which they share the
     largest border. All connected components smaller than min_area will be removed
@@ -217,7 +231,7 @@ def postrocessing(label_image, spare=[], verbose=True):
 
     # merge small components to neighbours
     regionmask = skimage.measure.label(label_image)
-    origlabels = np.unique(label_image)
+    origlabels = speedup_numpy_unique(label_image)
     origlabels_maxsub = np.zeros((max(origlabels) + 1,), dtype=np.uint32)  # will hold the largest component for a label
     regions = skimage.measure.regionprops(regionmask, label_image)
     regions.sort(key=lambda x: x.area)
@@ -237,7 +251,7 @@ def postrocessing(label_image, spare=[], verbose=True):
             bb = bbox_3D(regionmask == r.label)
             sub = regionmask[bb[0] : bb[1], bb[2] : bb[3], bb[4] : bb[5]]
             dil = ndimage.binary_dilation(sub == r.label)
-            neighbours, counts = np.unique(sub[dil], return_counts=True)
+            neighbours, counts = speedup_numpy_unique(sub[dil], return_counts=True)
             mapto = r.label
             maxmap = 0
             myarea = 0
@@ -265,7 +279,7 @@ def postrocessing(label_image, spare=[], verbose=True):
         holefiller = fill_voids.fill
 
     outmask = np.zeros(outmask_mapped.shape, dtype=np.uint8)
-    for i in np.unique(outmask_mapped)[1:]:
+    for i in speedup_numpy_unique(outmask_mapped)[1:]:
         outmask[holefiller(keep_largest_connected_component(outmask_mapped == i))] = i
 
     return outmask
@@ -335,7 +349,7 @@ def cv2_zoom(
     out_shape = tuple((np.asarray(img.shape[:2]) * np.asarray(scale)).round().astype(int)[::-1])
 
     if pseudo_linear:
-        uniques = np.unique(img)
+        uniques = speedup_numpy_unique(img)
         out_shape_with_channels = list(out_shape[::-1]) + list(img.shape[2:])
         out_img = np.zeros(out_shape_with_channels, dtype=img.dtype)
         for value in uniques[uniques != 0]:
diff --git a/requirements.txt b/requirements.txt
index e2679cc..ff748b7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,3 +8,4 @@ SimpleITK==1.2.4
 skimage==0.0
 fill_voids
 opencv-python-headless==4.5.3.56
+pandas
\ No newline at end of file