diff --git a/utils/raspberrypi/ctt/ctt.py b/utils/raspberrypi/ctt/ctt.py
index 93a8e8fb1..0b6789f29 100755
--- a/utils/raspberrypi/ctt/ctt.py
+++ b/utils/raspberrypi/ctt/ctt.py
@@ -736,13 +736,15 @@ def run_ctt(json_output, directory, config, log_output, json_template, grid_size
     try:
         Cam = Camera(json_output, json=json_template)
         Cam.log_user_input(json_output, directory, config, log_output)
-        if alsc_only:
-            disable = set(Cam.json.keys()).symmetric_difference({"rpi.alsc"})
-        Cam.disable = disable
-        Cam.plot = plot
         Cam.add_imgs(directory, mac_config, blacklevel)
     except FileNotFoundError:
         raise ArgError('\n\nError: Input image directory not found!')
+    if len(Cam.imgs) == 0 and len(Cam.imgs_cac) == 0 and len(Cam.imgs_alsc) > 0:
+        alsc_only = True
+    if alsc_only:
+        disable = set(Cam.json.keys()).symmetric_difference({"rpi.alsc"})
+    Cam.disable = disable
+    Cam.plot = plot
 
     """
     preform calibrations as long as check_imgs returns True
diff --git a/utils/raspberrypi/ctt/ctt_alsc.py b/utils/raspberrypi/ctt/ctt_alsc.py
index 5d8b2ced9..65abcb129 100644
--- a/utils/raspberrypi/ctt/ctt_alsc.py
+++ b/utils/raspberrypi/ctt/ctt_alsc.py
@@ -159,7 +159,7 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12), max_gain=8.0)
         cb = cb/np.min(cb)
         cg = cv2.medianBlur(cg, 3).astype('float64')
         cg = cg/np.min(cg)
-        cg = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
+        cg_clamp = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
 
         """
         debugging code showing 2D surface plot of vignetting. Quite useful for
@@ -183,7 +183,7 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12), max_gain=8.0)
             # print(Img.str)
             plt.show()
 
-        return Img.col, cr.flatten(), cb.flatten(), cg, (w, h, dx, dy)
+        return Img.col, cr.flatten(), cb.flatten(), cg_clamp, (w, h, dx, dy)
 
     else:
         """
@@ -193,17 +193,17 @@ def alsc(Cam, Img, do_alsc_colour, plot=False, grid_size=(16, 12), max_gain=8.0)
         cg = np.reshape(1/g, (grid_h, grid_w)).astype('float32')
         cg = cv2.medianBlur(cg, 3).astype('float64')
         cg = cg/np.min(cg)
-        cg = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
+        cg_clamp = [min(v, max_gain) for v in cg.flatten()]  # never exceed the max luminance gain
 
         if plot:
-            hf = plt.figure(figssize=(8, 8))
+            hf = plt.figure(figsize=(8, 8))
             ha = hf.add_subplot(1, 1, 1, projection='3d')
-            X, Y = np.meashgrid(range(grid_w), range(grid_h))
+            X, Y = np.meshgrid(range(grid_w), range(grid_h))
             ha.plot_surface(X, -Y, cg, cmap=cm.coolwarm, linewidth=0)
-            ha.set_title('ALSC Plot (Luminance only!)\nImg: {}\n\ncg').format(Img.str)
+            ha.set_title('ALSC Plot (Luminance only!)\nImg: {}\n\ncg'.format(Img.str))
             plt.show()
 
-        return Img.col, None, None, cg.flatten(), (w, h, dx, dy)
+        return Img.col, None, None, cg_clamp, (w, h, dx, dy)
 
 
 """
diff --git a/utils/raspberrypi/ctt/ctt_image_load.py b/utils/raspberrypi/ctt/ctt_image_load.py
index 531de328d..1842f2b32 100644
--- a/utils/raspberrypi/ctt/ctt_image_load.py
+++ b/utils/raspberrypi/ctt/ctt_image_load.py
@@ -322,14 +322,21 @@ def dng_load_image(Cam, im_str):
             photo = "Image"
         Img.pad = 0
         Img.h = metadata[f'Exif.{subimage}.ImageLength'].value
-        white = metadata[f'Exif.{subimage}.WhiteLevel'].value
+        try:
+            white = metadata[f'Exif.{subimage}.WhiteLevel'].value
+        except:
+            white = (1 << Img.sigbits) - 1
         Img.sigbits = int(white).bit_length()
         Img.fmt = (Img.sigbits - 4) // 2
         Img.exposure = int(metadata[f'Exif.{photo}.ExposureTime'].value * 1000000)
         Img.againQ8 = metadata[f'Exif.{photo}.ISOSpeedRatings'].value * 256 / 100
         Img.againQ8_norm = Img.againQ8 / 256
         Img.camName = metadata['Exif.Image.Model'].value
-        Img.blacklevel = int(metadata[f'Exif.{subimage}.BlackLevel'].value[0])
+        blacks = metadata[f'Exif.{subimage}.BlackLevel'].value
+        try:
+            Img.blacklevel = int(blacks[0])
+        except TypeError:
+            Img.blacklevel = int(blacks)
         Img.blacklevel_16 = Img.blacklevel << (16 - Img.sigbits)
         bayer_case = {
             '0 1 1 2': (0, (0, 1, 2, 3)),
@@ -337,9 +344,13 @@ def dng_load_image(Cam, im_str):
             '2 1 1 0': (2, (3, 2, 1, 0)),
             '1 0 2 1': (3, (1, 0, 3, 2))
         }
-        cfa_pattern = metadata[f'Exif.{subimage}.CFAPattern'].value
-        Img.pattern = bayer_case[cfa_pattern][0]
-        Img.order = bayer_case[cfa_pattern][1]
+        try:
+            cfa_pattern = metadata[f'Exif.{subimage}.CFAPattern'].value
+            Img.pattern = bayer_case[cfa_pattern][0]
+            Img.order = bayer_case[cfa_pattern][1]
+        except:
+            Img.pattern = 128
+            Img.order = (0, 1, 2, 3) # dummy order for mono images
 
         # Now use RawPy tp get the raw Bayer pixels
         raw_im = raw.imread(im_str)
@@ -358,6 +369,7 @@ def dng_load_image(Cam, im_str):
         Cam.log += '\nERROR: DNG file does not exist or is incompatible'
         raise
 
+    Img.str = im_str
     return Img