DAS-2280: Merge TRANSPARENT_IDX and NODATA_IDX to increase available …

…colors

CHANGELOG.md

@@ -4,6 +4,14 @@ HyBIG follows semantic versioning. All notable changes to this project will be
 documented in this file. The format is based on [Keep a
 Changelog](http://keepachangelog.com/en/1.0.0/).
 
+## [v2.2.0] - 2024-12-19
+
+### Changed
+
+* NODATA and TRANSPARENT values are merged.
+  - The user visible change is that now a paletted output PNG will have up to 254 color values and a 255th value that is transparent.
+  - Internally, the code change removes `TRANSPARENT_IDX` (254) and uses `NODATA_IDX` in its stead.  A color of (0,0,0,0) was already set to both of the indexes in the ouput PNGs. This ensures the roundtrip from single band to RGBA to Paletted PNG is consistent.
+
 ## [v2.1.0] - 2024-12-13
 
 ### Changed

hybig/browse.py

@@ -28,8 +28,6 @@
     NODATA_RGBA,
     OPAQUE,
     TRANSPARENT,
-    TRANSPARENT_IDX,
-    TRANSPARENT_RGBA,
     all_black_color_map,
     get_color_palette,
     palette_from_remote_colortable,
@@ -299,7 +297,7 @@ def convert_gray_1band_to_raster(data_array: DataArray) -> ndarray:
     """Convert a 1-band raster without a color association."""
     band = data_array[0, :, :]
     cmap = matplotlib.colormaps['Greys_r']
-    cmap.set_bad(TRANSPARENT_RGBA)
+    cmap.set_bad(NODATA_RGBA)
     norm = Normalize(vmin=np.nanmin(band), vmax=np.nanmax(band))
     scalar_map = ScalarMappable(cmap=cmap, norm=norm)
 
@@ -403,9 +401,9 @@ def palettize_raster(raster: ndarray) -> tuple[ndarray, dict]:
     written to the final raster as 254 and add the mapped RGBA value to the
     color palette.
     """
-    # reserves 254 for transparent images and 255 for off grid fill values
-    # 0 to 253
-    max_colors = 254
+    # reserves 255 for transparent and off grid fill values
+    # 0 to 254
+    max_colors = 255
     rgb_raster, alpha = remove_alpha(raster)
 
     multiband_image = Image.fromarray(reshape_as_image(rgb_raster))
@@ -427,8 +425,8 @@ def add_alpha(
     """
     if alpha is not None and np.any(alpha != OPAQUE):
         # Set any alpha to the transparent index value
-        quantized_array = np.where(alpha != OPAQUE, TRANSPARENT_IDX, quantized_array)
-        color_map[TRANSPARENT_IDX] = TRANSPARENT_RGBA
+        quantized_array = np.where(alpha != OPAQUE, NODATA_IDX, quantized_array)
+        color_map[NODATA_IDX] = NODATA_RGBA
     return quantized_array, color_map
 
 

hybig/color_utility.py

@@ -21,9 +21,6 @@
 # Applied to transparent pixels where alpha < 255
 TRANSPARENT = np.uint8(0)
 OPAQUE = np.uint8(255)
-TRANSPARENT_RGBA = (0, 0, 0, 0)
-TRANSPARENT_IDX = 254
-
 # Applied to off grid areas during reprojection
 NODATA_RGBA = (0, 0, 0, 0)
 NODATA_IDX = 255

tests/unit/test_browse.py

@@ -724,7 +724,7 @@ def test_palettize_raster_no_alpha_layer(self, get_color_map_mock, image_mock):
 
         out_raster, out_map = palettize_raster(raster)
 
-        multiband_image_mock.quantize.assert_called_once_with(colors=254)
+        multiband_image_mock.quantize.assert_called_once_with(colors=255)
         get_color_map_mock.assert_called_once_with(quantized_output)
 
         np.testing.assert_array_equal(expected_out_raster, out_raster, strict=True)
@@ -748,11 +748,11 @@ def test_palettize_raster_with_alpha_layer(self, get_color_map_mock, image_mock)
         multiband_image_mock.quantize.return_value = quantized_output
 
         expected_out_raster = np.array(quantized_output).reshape(1, 10, 11)
-        expected_out_raster[0, 0:3, 0:3] = 254
+        expected_out_raster[0, 0:3, 0:3] = 255
 
         out_raster, out_map = palettize_raster(raster)
 
-        multiband_image_mock.quantize.assert_called_once_with(colors=254)
+        multiband_image_mock.quantize.assert_called_once_with(colors=255)
         get_color_map_mock.assert_called_once_with(quantized_output)
 
         np.testing.assert_array_equal(expected_out_raster, out_raster, strict=True)