patch: apply scale/offset to statistis (#812)

Author: vincentsarago

rio_tiler/reader.py

@@ -297,6 +297,19 @@ def read(
             numpy.multiply(data, scales, out=data, casting="unsafe")
             numpy.add(data, offsets, out=data, casting="unsafe")
 
+            # apply scale/offsets to stats
+            if dataset_statistics:
+                scales = numpy.array(dataset.scales)[numpy.array(indexes) - 1].reshape(
+                    (-1, 1)
+                )
+                offsets = numpy.array(dataset.offsets)[numpy.array(indexes) - 1].reshape(
+                    (-1, 1)
+                )
+                stats_array = numpy.array(dataset_statistics)
+                numpy.multiply(stats_array, scales, out=stats_array, casting="unsafe")
+                numpy.add(stats_array, offsets, out=stats_array, casting="unsafe")
+                dataset_statistics = [tuple(s) for s in stats_array.tolist()]
+
         if post_process:
             data = post_process(data)
 

tests/fixtures/cog_scale_stats.tif

@@ -38,6 +38,7 @@
 COG_TAGS = os.path.join(PREFIX, "cog_tags.tif")
 COG_NODATA = os.path.join(PREFIX, "cog_nodata.tif")
 COG_SCALE = os.path.join(PREFIX, "cog_scale.tif")
+COG_SCALE_STATS = os.path.join(PREFIX, "cog_scale_stats.tif")
 COG_GCPS = os.path.join(PREFIX, "cog_gcps.tif")
 COG_DLINE = os.path.join(PREFIX, "cog_dateline.tif")
 COG_EARTH = os.path.join(PREFIX, "cog_fullearth.tif")
@@ -1163,3 +1164,21 @@ def test_titiler_issue_1163_warpedVrt():
             (75.0, 9.0, 77.0, 10.0), bounds_crs="epsg:4326", width=500, height=500
         )
         assert img.statistics()["b1"].valid_percent
+
+
+def test_unscale_stats():
+    """check if scale/offset were applied on stats."""
+    with Reader(COG_SCALE_STATS) as src:
+        img = src.read(unscale=True)
+        stats = img.statistics()
+        minb1, maxb1 = stats["b1"].min, stats["b1"].max
+
+        assert pytest.approx(img.dataset_statistics[0][0]) == pytest.approx(minb1)
+        assert pytest.approx(img.dataset_statistics[0][1]) == pytest.approx(maxb1)
+
+        img = src.read()
+        stats = img.statistics()
+        minb1, maxb1 = stats["b1"].min, stats["b1"].max
+
+        assert pytest.approx(img.dataset_statistics[0][0]) == pytest.approx(minb1)
+        assert pytest.approx(img.dataset_statistics[0][1]) == pytest.approx(maxb1)