diff --git a/creader/SparseFile.py b/creader/SparseFile.py
new file mode 100644
index 0000000..4d0f9c8
--- /dev/null
+++ b/creader/SparseFile.py
@@ -0,0 +1,14 @@
+import numpy as np
+
+def to_sparse(data, th = 0):
+    """
+    Convert frames stack ndarray[frame, row, col] to sparse array.
+    Warning: this function drops the frame numbers and only keeps row, col, energy
+    """
+    sparse_dt = [('row', np.int16), ('col', np.int16), ('energy', data.dtype)]
+    size = (data>th).sum()
+    sparse = np.zeros(size, sparse_dt)
+    frames, rows, cols = np.where(data>th)
+    for i,(f,r,c) in enumerate(zip(frames, rows, cols)):
+        sparse[i] = (r, c, data[f,r,c])
+    return sparse
diff --git a/creader/__init__.py b/creader/__init__.py
index 47f8a42..609c0d1 100644
--- a/creader/__init__.py
+++ b/creader/__init__.py
@@ -4,4 +4,6 @@ from _creader import *
 from .file_utils import open_file
 from .ClusterFile import ClusterFile
 from .enums import DetectorType
-from .RawFile import RawFile
\ No newline at end of file
+from .RawFile import RawFile
+
+from .SparseFile import to_sparse
\ No newline at end of file