feat: adding an alpha mask to ortho map tiles for pixels in the tile …

…but outside the image

.coveragerc

@@ -17,4 +17,4 @@ partial_branches =
 
 show_missing = True
 
-fail_under = 60
+fail_under = 96

src/aws/osml/image_processing/gdal_tile_factory.py

@@ -246,20 +246,53 @@ def find_appropriate_r_level(src_bbox, tile_width) -> int:
         map2 = src_y_interpolator(dst_x, dst_y).astype(np.float32)
 
         logger.debug(
-            f"Sanity check remap array sizes. " f"They should match the desired map tile size {tile_size[0]}x{tile_size[1]}"
+            f"Sanity check remap array sizes. They should match the desired map tile size {tile_size[0]}x{tile_size[1]}"
         )
         logger.debug(f"map1.shape = {map1.shape}")
         logger.debug(f"map2.shape = {map2.shape}")
 
-        dst = cv2.remap(src, map1, map2, cv2.INTER_LINEAR)
+        # Set the scalar for out of bounds pixels to 0 and bias the image just slightly such that all values
+        # of 0 in the output are only from out of bounds pixels.  Valid range for the scalar is 0-255 [int|tuple].
+        scalar = 0
+        if src.ndim == 2:  # 1-band grayscale
+            src[src == 0] = 1
+        elif src.ndim >= 3 and src.shape[2] == 3:  # 3-band
+            scalar = (0, 0, 0)
+            src[(src == [0, 0, 0]).all(axis=2)] = [0, 0, 1]
+        logger.debug(f"scalar = {scalar}")
+
+        # Transform image
+        dst = cv2.remap(src, map1, map2, cv2.INTER_LINEAR, borderMode=cv2.BORDER_CONSTANT, borderValue=scalar)
+
+        # Create alpha layer mask
+        alpha_mask = None
+        if dst.ndim == 2:  # 1-band grayscale
+            all_channel_pixels_mask = dst != 0
+            alpha_mask = np.zeros_like(dst, dtype=np.uint8)
+            alpha_mask[all_channel_pixels_mask] = 255
+        elif dst.ndim >= 3 and dst.shape[2] == 3:  # 3-band
+            all_channel_pixels_mask = np.all(dst != 0, axis=2)
+            alpha_mask = np.zeros_like(dst[..., 0], dtype=np.uint8)
+            alpha_mask[all_channel_pixels_mask] = 255
+        if alpha_mask is not None:  # arrays with zeros/zero size can be falsy so explicitly check None
+            logger.debug(f"alpha_mask.shape = {alpha_mask.shape}")
+        elif dst.ndim > 2:
+            logger.debug(f"alpha_mask = None.  Image has {dst.ndim} dimensions and {dst.shape[2]} bands.")
+        else:
+            logger.debug(f"alpha_mask = None.  Image has {dst.ndim} dimensions.")
+
         output_tile_pixels = self._create_display_image(dst)
 
+        if alpha_mask is not None:
+            # imencode does not support 2-band (grayscale + alpha) so the workaround is to convert to 3-band
+            if output_tile_pixels.ndim == 2:
+                output_tile_pixels = np.dstack((output_tile_pixels, output_tile_pixels, output_tile_pixels))
+            # add alpha mask
+            output_tile_pixels = np.dstack((output_tile_pixels, alpha_mask))
+
         # TODO: Formats other than PNG?
         is_success, image_bytes = cv2.imencode(".png", output_tile_pixels)
-        if is_success:
-            return image_bytes
-        else:
-            return None
+        return image_bytes if is_success else None
 
     def _read_from_rlevel_as_array(
         self, scaled_bbox: Tuple[int, int, int, int], r_level: int, band_numbers: Optional[List[int]] = None

test/aws/osml/image_processing/test_gdal_tile_factory.py

@@ -223,6 +223,31 @@ def test_create_map_tiles_for_image(self):
                 assert tile_dataset.RasterYSize == 256
                 assert tile_dataset.GetDriver().ShortName == GDALImageFormats.PNG
 
+    def test_create_map_tiles_for_color_image(self):
+        tile_set_id = "WebMercatorQuad"
+        tile_set = MapTileSetFactory.get_for_id(tile_set_id)
+        full_dataset, sensor_model = load_gdal_dataset("./test/data/small.tif")
+        tile_factory = GDALTileFactory(
+            full_dataset,
+            sensor_model,
+            GDALImageFormats.PNG,
+            GDALCompressionOptions.NONE,
+            output_type=gdalconst.GDT_Byte,
+            range_adjustment=RangeAdjustmentType.DRA,
+        )
+        tile_matrix = 14
+        tile_row = 10830
+        tile_col = 8437
+        map_tile = tile_set.get_tile(MapTileId(tile_matrix=tile_matrix, tile_row=tile_row, tile_col=tile_col))
+        encoded_tile_data = tile_factory.create_orthophoto_tile(geo_bbox=map_tile.bounds, tile_size=map_tile.size)
+        assert encoded_tile_data is not None
+        temp_ds_name = "/vsimem/" + token_hex(16) + ".PNG"
+        gdal.FileFromMemBuffer(temp_ds_name, encoded_tile_data)
+        tile_dataset = gdal.Open(temp_ds_name)
+        assert tile_dataset.RasterXSize == 256
+        assert tile_dataset.RasterYSize == 256
+        assert tile_dataset.GetDriver().ShortName == GDALImageFormats.PNG
+
 
 if __name__ == "__main__":
     unittest.main()