Fixed reading 10-bit PGM

Tests/test_file_ppm.py

@@ -20,6 +20,16 @@ def test_sanity():
         assert im.get_format_mimetype() == "image/x-portable-pixmap"
 
 
+def test_10bit_pgm():
+    with Image.open("Tests/images/10_bit_binary.pgm") as im:
+        im.load()
+        assert im.mode == "I"
+        assert im.size == (128, 128)
+        assert im.get_format_mimetype() == "image/x-portable-graymap"
+
+        assert_image_equal_tofile(im, "Tests/images/10_bit_binary_pgm.png")
+
+
 def test_16bit_pgm():
     with Image.open("Tests/images/16_bit_binary.pgm") as im:
         im.load()

src/PIL/PpmImagePlugin.py

@@ -113,9 +113,12 @@ class PpmImageFile(ImageFile.ImageFile):
             elif ix == 2:  # token is maxval
                 maxval = token
                 if maxval > 255:
-                    if not mode == "L":
+                    if mode != "L":
                         raise ValueError(f"Too many colors for band: {token}")
-                    if maxval < 2**16:
+                    if maxval == 1023:
+                        self.mode = "I"
+                        rawmode = "I;10B"
+                    elif maxval < 2**16:
                         self.mode = "I"
                         rawmode = "I;16B"
                     else:

src/libImaging/Unpack.c

@@ -1182,6 +1182,23 @@ unpackI12_I16(UINT8 *out, const UINT8 *in, int pixels) {
     }
 }
 
+static void
+unpackI10B(UINT8 *out, const UINT8 *in, int pixels) {
+    int i, pixel;
+    for (i = 0; i < pixels; i++) {
+        pixel = ((in[0] << 8) + in[1]) << 6;
+#ifdef WORDS_BIGENDIAN
+        out[2] = pixel >> 8;
+        out[3] = pixel;
+#else
+        out[0] = pixel;
+        out[1] = pixel >> 8;
+#endif
+        in += 2;
+        out += 4;
+    }
+}
+
 static void
 copy1(UINT8 *out, const UINT8 *in, int pixels) {
     /* L, P */
@@ -1684,6 +1701,7 @@ static struct {
     {"I", "I", 32, copy4},
     {"I", "I;8", 8, unpackI8},
     {"I", "I;8S", 8, unpackI8S},
+    {"I", "I;10B", 16, unpackI10B},
     {"I", "I;16", 16, unpackI16},
     {"I", "I;16S", 16, unpackI16S},
     {"I", "I;16B", 16, unpackI16B},