check if discrete colormap has negative values (#492)

CHANGES.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 * Switch to `pyproject.toml` and `flit` for packaging
+* Catch discrete colormap with negative values
 
 # 3.1.2 (2022-03-25)
 

rio_tiler/colormap.py

@@ -102,7 +102,7 @@ def apply_cmap(data: numpy.ndarray, colormap: ColorMapType) -> DataMaskType:
     # rio_tiler.colormap.make_lut, because we don't want to create a `lookup table`
     # with more than 256 entries (256 x 4) array. In this case we use `apply_discrete_cmap`
     # which can work with arbitrary colormap dict.
-    if len(colormap) > 256 or max(colormap) >= 256:
+    if len(colormap) > 256 or max(colormap) >= 256 or min(colormap) < 0:
         return apply_discrete_cmap(data, colormap)
 
     lookup_table = make_lut(colormap)

tests/test_cmap.py

@@ -164,13 +164,22 @@ def test_apply_discrete_cmap():
     cm = deepcopy(colormap.EMPTY_COLORMAP)
     cm.pop(255)
     cm[1000] = (255, 255, 255, 255)
-
     d, m = colormap.apply_cmap(data, cm)
     dd, mm = colormap.apply_discrete_cmap(data, cm)
+    numpy.testing.assert_array_equal(dd, d)
+    numpy.testing.assert_array_equal(mm, m)
 
     cm = {1: (0, 0, 0, 255), 256: (255, 255, 255, 255)}
     assert colormap.apply_cmap(data, cm)
 
+    # Test with negative value
+    cm = {-100: (255, 255, 255, 255), 1: (0, 0, 0, 255), 256: (255, 255, 255, 255)}
+    data[0, 5:, 5:] = -100
+    d, m = colormap.apply_cmap(data, cm)
+    dd, mm = colormap.apply_discrete_cmap(data, cm)
+    numpy.testing.assert_array_equal(dd, d)
+    numpy.testing.assert_array_equal(mm, m)
+
 
 def test_apply_intervals_cmap():
     """Should return valid data and mask."""