Added dedicated unpacker for inverted alpha

Author: radarhere

src/PIL/TgaImagePlugin.py

@@ -36,7 +36,7 @@
     (3, 1): "1",
     (3, 8): "L",
     (3, 16): "LA",
-    (2, 16): "BGRA;15",
+    (2, 16): "BGRA;15Z",
     (2, 24): "BGR",
     (2, 32): "BGRA",
 }
@@ -87,9 +87,7 @@ def _open(self) -> None:
         elif imagetype in (1, 9):
             self._mode = "P" if colormaptype else "L"
         elif imagetype in (2, 10):
-            self._mode = "RGB"
-            if depth == 32:
-                self._mode = "RGBA"
+            self._mode = "RGB" if depth == 24 else "RGBA"
         else:
             msg = "unknown TGA mode"
             raise SyntaxError(msg)
@@ -117,11 +115,9 @@ def _open(self) -> None:
             # read palette
             start, size, mapdepth = i16(s, 3), i16(s, 5), s[7]
             if mapdepth == 16:
-                colormap = self.fp.read(2 * size)
-                palette_data = bytearray(2 * start)
-                for a, b in zip(colormap[::2], colormap[1::2]):
-                    palette_data += bytearray((a, b ^ 128))
-                self.palette = ImagePalette.raw("BGRA;15", bytes(palette_data))
+                self.palette = ImagePalette.raw(
+                    "BGRA;15Z", bytes(2 * start) + self.fp.read(2 * size)
+                )
                 self.palette.mode = "RGBA"
             elif mapdepth == 24:
                 self.palette = ImagePalette.raw(

src/libImaging/Unpack.c

@@ -718,6 +718,21 @@ ImagingUnpackBGRA15(UINT8 *out, const UINT8 *in, int pixels) {
     }
 }
 
+void
+ImagingUnpackBGRA15Z(UINT8 *out, const UINT8 *in, int pixels) {
+    int i, pixel;
+    /* RGB, rearranged channels, 5/5/5/1 bits per pixel, inverted alpha */
+    for (i = 0; i < pixels; i++) {
+        pixel = in[0] + (in[1] << 8);
+        out[B] = (pixel & 31) * 255 / 31;
+        out[G] = ((pixel >> 5) & 31) * 255 / 31;
+        out[R] = ((pixel >> 10) & 31) * 255 / 31;
+        out[A] = ~((pixel >> 15) * 255);
+        out += 4;
+        in += 2;
+    }
+}
+
 void
 ImagingUnpackRGB16(UINT8 *out, const UINT8 *in, int pixels) {
     int i, pixel;
@@ -1538,7 +1553,7 @@ static struct {
 
     /* flags: "I" inverted data; "R" reversed bit order; "B" big
        endian byte order (default is little endian); "L" line
-       interleave, "S" signed, "F" floating point */
+       interleave, "S" signed, "F" floating point, "Z" inverted alpha */
 
     /* exception: rawmodes "I" and "F" are always native endian byte order */
 
@@ -1646,6 +1661,7 @@ static struct {
     {"RGBA", "RGBA;L", 32, unpackRGBAL},
     {"RGBA", "RGBA;15", 16, ImagingUnpackRGBA15},
     {"RGBA", "BGRA;15", 16, ImagingUnpackBGRA15},
+    {"RGBA", "BGRA;15Z", 16, ImagingUnpackBGRA15Z},
     {"RGBA", "RGBA;4B", 16, ImagingUnpackRGBA4B},
     {"RGBA", "RGBA;16L", 64, unpackRGBA16L},
     {"RGBA", "RGBA;16B", 64, unpackRGBA16B},