Open 16-bit grayscale PNGs as I;16

Tests/test_file_mcidas.py

@@ -19,7 +19,7 @@ def test_valid_file() -> None:
     # https://ghrc.nsstc.nasa.gov/hydro/details/cmx3g8
     # https://ghrc.nsstc.nasa.gov/pub/fieldCampaigns/camex3/cmx3g8/browse/
     test_file = "Tests/images/cmx3g8_wv_1998.260_0745_mcidas.ara"
-    saved_file = "Tests/images/cmx3g8_wv_1998.260_0745_mcidas.png"
+    saved_file = "Tests/images/cmx3g8_wv_1998.260_0745_mcidas.tiff"
 
     # Act
     with Image.open(test_file) as im:

Tests/test_file_png.py

@@ -102,7 +102,7 @@ class TestFilePng:
             im = hopper(mode)
             im.save(test_file)
             with Image.open(test_file) as reloaded:
-                if mode in ("I;16", "I;16B"):
+                if mode in ("I", "I;16B"):
                     reloaded = reloaded.convert(mode)
                 assert_image_equal(reloaded, im)
 
@@ -304,8 +304,8 @@ class TestFilePng:
         assert im.getcolors() == [(100, (0, 0, 0, 0))]
 
     def test_save_grayscale_transparency(self, tmp_path: Path) -> None:
-        for mode, num_transparent in {"1": 1994, "L": 559, "I": 559}.items():
-            in_file = "Tests/images/" + mode.lower() + "_trns.png"
+        for mode, num_transparent in {"1": 1994, "L": 559, "I;16": 559}.items():
+            in_file = "Tests/images/" + mode.split(";")[0].lower() + "_trns.png"
             with Image.open(in_file) as im:
                 assert im.mode == mode
                 assert im.info["transparency"] == 255

Tests/test_file_ppm.py

@@ -88,7 +88,7 @@ def test_16bit_pgm() -> None:
         assert im.size == (20, 100)
         assert im.get_format_mimetype() == "image/x-portable-graymap"
 
-        assert_image_equal_tofile(im, "Tests/images/16_bit_binary_pgm.png")
+        assert_image_equal_tofile(im, "Tests/images/16_bit_binary_pgm.tiff")
 
 
 def test_16bit_pgm_write(tmp_path: Path) -> None:

Tests/test_image_filter.py

@@ -148,9 +148,7 @@ def test_kernel_not_enough_coefficients() -> None:
 @pytest.mark.parametrize("mode", ("L", "LA", "I", "RGB", "CMYK"))
 def test_consistency_3x3(mode: str) -> None:
     with Image.open("Tests/images/hopper.bmp") as source:
-        reference_name = "hopper_emboss"
-        reference_name += "_I.png" if mode == "I" else ".bmp"
-        with Image.open("Tests/images/" + reference_name) as reference:
+        with Image.open("Tests/images/hopper_emboss.bmp") as reference:
             kernel = ImageFilter.Kernel(
                 (3, 3),
                 # fmt: off
@@ -160,23 +158,13 @@ def test_consistency_3x3(mode: str) -> None:
                 # fmt: on
                 0.3,
             )
-            source = source.split() * 2
-            reference = reference.split() * 2
-
-            if mode == "I":
-                source = source[0].convert(mode)
-            else:
-                source = Image.merge(mode, source[: len(mode)])
-            reference = Image.merge(mode, reference[: len(mode)])
             assert_image_equal(source.filter(kernel), reference)
 
 
 @pytest.mark.parametrize("mode", ("L", "LA", "I", "RGB", "CMYK"))
 def test_consistency_5x5(mode: str) -> None:
     with Image.open("Tests/images/hopper.bmp") as source:
-        reference_name = "hopper_emboss_more"
-        reference_name += "_I.png" if mode == "I" else ".bmp"
-        with Image.open("Tests/images/" + reference_name) as reference:
+        with Image.open("Tests/images/hopper_emboss_more.bmp") as reference:
             kernel = ImageFilter.Kernel(
                 (5, 5),
                 # fmt: off
@@ -188,14 +176,6 @@ def test_consistency_5x5(mode: str) -> None:
                 # fmt: on
                 0.3,
             )
-            source = source.split() * 2
-            reference = reference.split() * 2
-
-            if mode == "I":
-                source = source[0].convert(mode)
-            else:
-                source = Image.merge(mode, source[: len(mode)])
-            reference = Image.merge(mode, reference[: len(mode)])
             assert_image_equal(source.filter(kernel), reference)
 
 

Tests/test_imagedraw.py

@@ -753,7 +753,7 @@ def test_rectangle_I16(bbox: Coords) -> None:
     draw.rectangle(bbox, outline=0xFFFF)
 
     # Assert
-    assert_image_equal_tofile(im.convert("I"), "Tests/images/imagedraw_rectangle_I.png")
+    assert_image_equal_tofile(im, "Tests/images/imagedraw_rectangle_I.tiff")
 
 
 @pytest.mark.parametrize("bbox", BBOX)

src/PIL/Image.py

@@ -978,7 +978,7 @@ class Image:
         delete_trns = False
         # transparency handling
         if has_transparency:
-            if (self.mode in ("1", "L", "I") and mode in ("LA", "RGBA")) or (
+            if (self.mode in ("1", "L", "I", "I;16") and mode in ("LA", "RGBA")) or (
                 self.mode == "RGB" and mode == "RGBA"
             ):
                 # Use transparent conversion to promote from transparent

src/PIL/PngImagePlugin.py

@@ -62,7 +62,7 @@ _MODES = {
     (2, 0): ("L", "L;2"),
     (4, 0): ("L", "L;4"),
     (8, 0): ("L", "L"),
-    (16, 0): ("I", "I;16B"),
+    (16, 0): ("I;16", "I;16B"),
     # Truecolour
     (8, 2): ("RGB", "RGB"),
     (16, 2): ("RGB", "RGB;16B"),
@@ -467,7 +467,7 @@ class PngStream(ChunkStream):
                 # otherwise, we have a byte string with one alpha value
                 # for each palette entry
                 self.im_info["transparency"] = s
-        elif self.im_mode in ("1", "L", "I"):
+        elif self.im_mode in ("1", "L", "I;16"):
             self.im_info["transparency"] = i16(s)
         elif self.im_mode == "RGB":
             self.im_info["transparency"] = i16(s), i16(s, 2), i16(s, 4)
@@ -1356,7 +1356,7 @@ def _save(im, fp, filename, chunk=putchunk, save_all=False):
                 transparency = max(0, min(255, transparency))
                 alpha = b"\xFF" * transparency + b"\0"
                 chunk(fp, b"tRNS", alpha[:alpha_bytes])
-        elif im.mode in ("1", "L", "I"):
+        elif im.mode in ("1", "L", "I", "I;16"):
             transparency = max(0, min(65535, transparency))
             chunk(fp, b"tRNS", o16(transparency))
         elif im.mode == "RGB":

src/libImaging/Convert.c

@@ -878,6 +878,18 @@ I16B_L(UINT8 *out, const UINT8 *in, int xsize) {
     }
 }
 
+static void
+I16_RGB(UINT8 *out, const UINT8 *in, int xsize) {
+    int x;
+    for (x = 0; x < xsize; x++, in += 2) {
+        UINT8 v = in[1] == 0 ? in[0] : 255;
+        *out++ = v;
+        *out++ = v;
+        *out++ = v;
+        *out++ = 255;
+    }
+}
+
 static struct {
     const char *from;
     const char *to;
@@ -978,6 +990,7 @@ static struct {
 
     {"I", "I;16", I_I16L},
     {"I;16", "I", I16L_I},
+    {"I;16", "RGB", I16_RGB},
     {"L", "I;16", L_I16L},
     {"I;16", "L", I16L_L},
 
@@ -1678,6 +1691,7 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
         convert = rgb2rgba;
     } else if ((strcmp(imIn->mode, "1") == 0 ||
                 strcmp(imIn->mode, "I") == 0 ||
+                strcmp(imIn->mode, "I;16") == 0 ||
                 strcmp(imIn->mode, "L") == 0
                ) && (
                 strcmp(mode, "RGBA") == 0 ||
@@ -1687,6 +1701,8 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
             convert = bit2rgb;
         } else if (strcmp(imIn->mode, "I") == 0) {
             convert = i2rgb;
+        } else if (strcmp(imIn->mode, "I;16") == 0) {
+            convert = I16_RGB;
         } else {
             convert = l2rgb;
         }