diff --git a/pixel_mask_analysis.py b/pixel_mask_analysis.py
new file mode 100755
index 0000000..3fd71bb
--- /dev/null
+++ b/pixel_mask_analysis.py
@@ -0,0 +1,109 @@
+#!/usr/bin/env python
+
+import argparse
+import h5py
+import numpy as np
+from matplotlib import pyplot as plt
+
+
+def get_bit_values(img):
+    vmax = img.max()
+    maxbit = int(vmax).bit_length()
+    uniq = np.unique(img)
+    res = []
+    for bit in range(maxbit):
+        bv = (1 << bit)
+        if any(uniq & bv):
+            res.append(bv)
+    return res
+
+
+def calc_square_plots(n_plots):
+    nrows = int(round(np.sqrt(n_plots)))
+    ncols = int(np.ceil(n_plots / nrows))
+    return nrows, ncols
+
+
+def make_reasons():
+    # this should not be needed, but there is overlap in the reasons
+    class Trict(dict):
+        def __setitem__(self, key, value):
+            if key not in self:
+                super().__setitem__(key, [])
+            super().__getitem__(key).append(value)
+            print(key, super().__getitem__(key))
+
+    reasons = Trict()
+
+    reasons[5] = "additional pixel mask"
+
+    for index, gain in enumerate((0, 1, 3)):
+        reasons[index + 6] = f"std dev of gain {gain}"
+
+    for hg0 in (False, True):
+        for gain in range(4):
+            reasons[gain + 4 * hg0] = f"wrong gain ({gain=})" if not hg0 else f"wrong gain ({gain=}, hg0)"
+
+    res = {}
+    for k, v in sorted(reasons.items()):
+        v = " / ".join(v) # this should not be needed
+        res[1 << k] = v
+
+    return res
+
+
+def print_dict(d):
+    for i, (k, v) in enumerate(sorted(d.items())):
+        print(i, k, v, sep="\t")
+
+
+
+
+
+parser = argparse.ArgumentParser(description="Analyse the pixel mask of a pedestal file")
+parser.add_argument("fname", help="Path to a pedestal file")
+clargs = parser.parse_args()
+
+
+with h5py.File(clargs.fname) as f:
+    image = f["pixel_mask"][()]
+
+values = get_bit_values(image)
+
+n_plots = len(values) + 2
+nrows, ncols = calc_square_plots(n_plots)
+_fig, axs = plt.subplots(nrows, ncols, sharex=True, sharey=True)
+axs = iter(axs.flatten())
+
+def plot(img, title):
+    ax = next(axs)
+    ax.imshow(img, cmap="turbo")
+    ax.set_title(title)
+    print(f"{img.sum()} x {title}")
+
+
+plot(image, "raw")
+
+mask = image.astype(bool)
+plot(mask, "mask")
+
+
+reasons = make_reasons()
+for val in values:
+    selected = (image & val) == 0
+    reason = reasons[val]
+    plot(selected, f"{val} | {val:b} | {reason}")
+
+
+print()
+print_dict(reasons)
+
+
+plt.tight_layout()
+try:
+    plt.show()
+except KeyboardInterrupt:
+    pass
+
+
+
diff --git a/write_fake_example.py b/write_fake_example.py
new file mode 100755
index 0000000..20e3241
--- /dev/null
+++ b/write_fake_example.py
@@ -0,0 +1,25 @@
+#!/usr/bin/env python
+
+import h5py
+import numpy as np
+
+
+#image = np.zeros((512, 1024), dtype=int)
+image = np.zeros((10, 10), dtype=int)
+
+values = [3, 11, 128]
+#N = 10000 # per value
+N = 10 # per value
+
+width = max(values).bit_length()
+
+for val in values:
+    print(f"{val:0{width}b}")
+    idx = np.random.choice(image.size, size=N, replace=False)
+    image.flat[idx] = val
+
+with h5py.File("example.h5", "x") as f:
+    f["pixel_mask"] = image
+
+
+