Now using the rgbT2rgba conversion for L+transparency to RGBA, dropping the palette hack

PIL/Image.py

@@ -721,18 +721,8 @@ class Image:
         if dither is None:
             dither = FLOYDSTEINBERG
 
-        # fake a P-mode image, otherwise the transparency will get lost as there is
-        # currently no other way to convert transparency into an RGBA image
-        if self.mode == "L" and mode == "RGBA" and "transparency" in self.info:
-            from PIL import ImagePalette
-            self.mode = "P"
-            bytePalette = bytes(bytearray([i//3 for i in range(768)]))
-            self.palette = ImagePalette.raw("RGB", bytePalette)
-            self.palette.dirty = 1
-            self.load()
-
         # Use transparent conversion to promote from transparent color to an alpha channel.
-        if self.mode == "RGB" and mode == "RGBA" and "transparency" in self.info:
+        if self.mode in ("L", "RGB") and mode == "RGBA" and "transparency" in self.info:
             return self._new(self.im.convert_transparent(mode, self.info['transparency']))
             
         try:

Tests/test_file_png.py

@@ -182,6 +182,10 @@ def test_save_l_transparency():
     file = tempfile("temp.png")
     assert_no_exception(lambda: im.save(file))
 
+    # There are 559 transparent pixels. 
+    im = im.convert('RGBA')
+    assert_equal(im.split()[3].getcolors()[0][0], 559)
+
 def test_save_rgb_single_transparency():
     in_file = "Tests/images/caption_6_33_22.png"
     im = Image.open(in_file)

_imaging.c

@@ -799,12 +799,15 @@ _convert_transparent(ImagingObject* self, PyObject* args)
 {
     char* mode;
     int r,g,b;
-    if (!PyArg_ParseTuple(args, "s(iii)", &mode, &r, &g, &b)) {
+    if (PyArg_ParseTuple(args, "s(iii)", &mode, &r, &g, &b)) {
-        return NULL;
-    }
-
         return PyImagingNew(ImagingConvertTransparent(self->image, mode, r, g, b));
     }
+    PyErr_Clear();
+    if (PyArg_ParseTuple(args, "si", &mode, &r)) {
+        return PyImagingNew(ImagingConvertTransparent(self->image, mode, r, 0, 0));
+    }
+    return NULL;
+}
 
 static PyObject*
 _copy(ImagingObject* self, PyObject* args)

libImaging/Convert.c

@@ -319,7 +319,7 @@ rgba2rgbA(UINT8* out, const UINT8* in, int xsize)
  */
  
 static void
-rgbT2rgba(UINT8* out, const UINT8* in, int xsize, int r, int g, int b) 
+rgbT2rgba(UINT8* out, int xsize, int r, int g, int b) 
 {
 #ifdef WORDS_BIGENDIAN
     UINT32 trns = ((r & 0xff)<<24) | ((g & 0xff)<<16) | ((b & 0xff)<<8) | 0xff;
@@ -332,8 +332,6 @@ rgbT2rgba(UINT8* out, const UINT8* in, int xsize, int r, int g, int b)
     UINT32* tmp = (UINT32 *)out;
     int i;
 
-    rgb2rgba(out, in, xsize);
-
     for (i=0; i < xsize; i++ ,tmp++) {
         if (tmp[0]==trns) {
             tmp[0]=repl;
@@ -342,7 +340,6 @@ rgbT2rgba(UINT8* out, const UINT8* in, int xsize, int r, int g, int b)
 }
     
 
-
 /* ---------------- */
 /* CMYK conversions */
 /* ---------------- */
@@ -1197,6 +1194,7 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
                           int r, int g, int b)
 {
     ImagingSectionCookie cookie;
+    ImagingShuffler convert;
     Imaging imOut = NULL;
     int y;
 
@@ -1204,7 +1202,9 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
         return (Imaging) ImagingError_ModeError();
     }
     
-    if (!(strcmp(imIn->mode, "RGB") == 0 && strcmp(mode, "RGBA") == 0))
+    if (!((strcmp(imIn->mode, "RGB") == 0 || 
+           strcmp(imIn->mode, "L") == 0) 
+          && strcmp(mode, "RGBA") == 0))
 #ifdef notdef
     {
         return (Imaging) ImagingError_ValueError("conversion not supported");
@@ -1218,6 +1218,12 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
     }
 #endif
 
+    if (strcmp(imIn->mode, "RGB") == 0) {
+        convert = rgb2rgba;
+    } else {
+        convert = l2rgb;
+        g = b = r;
+    }
 
     imOut = ImagingNew2(mode, imOut, imIn);
     if (!imOut){
@@ -1225,9 +1231,11 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
     }
 
     ImagingSectionEnter(&cookie);
-    for (y = 0; y < imIn->ysize; y++)
+    for (y = 0; y < imIn->ysize; y++) {
-        rgbT2rgba((UINT8*) imOut->image[y], (UINT8*) imIn->image[y],
+        (*convert)((UINT8*) imOut->image[y], (UINT8*) imIn->image[y],
-                  imIn->xsize, r, g, b);
+                   imIn->xsize);
+        rgbT2rgba((UINT8*) imOut->image[y], imIn->xsize, r, g, b);
+    }
     ImagingSectionLeave(&cookie);
 
     return imOut;