Loading transparent pixels in C from subsequent GIF frames is no longer a problem

src/PIL/GifImagePlugin.py

@@ -313,18 +313,14 @@ class GifImageFile(ImageFile.ImageFile):
             pass
 
         if interlace is not None:
-            transparency = -1
+            if frame == 0 and frame_transparency is not None:
-            if frame_transparency is not None:
+                self.info["transparency"] = frame_transparency
-                if frame == 0:
-                    self.info["transparency"] = frame_transparency
-                else:
-                    transparency = frame_transparency
             self.tile = [
                 (
                     "gif",
                     (x0, y0, x1, y1),
                     self.__offset,
-                    (bits, interlace, transparency),
+                    (bits, interlace),
                 )
             ]
         else:

src/decode.c

@@ -433,8 +433,7 @@ PyImaging_GifDecoderNew(PyObject *self, PyObject *args) {
     char *mode;
     int bits = 8;
     int interlace = 0;
-    int transparency = -1;
+    if (!PyArg_ParseTuple(args, "s|ii", &mode, &bits, &interlace)) {
-    if (!PyArg_ParseTuple(args, "s|iii", &mode, &bits, &interlace, &transparency)) {
         return NULL;
     }
 
@@ -452,7 +451,6 @@ PyImaging_GifDecoderNew(PyObject *self, PyObject *args) {
 
     ((GIFDECODERSTATE *)decoder->state.context)->bits = bits;
     ((GIFDECODERSTATE *)decoder->state.context)->interlace = interlace;
-    ((GIFDECODERSTATE *)decoder->state.context)->transparency = transparency;
 
     return (PyObject *)decoder;
 }

src/libImaging/Gif.h

@@ -30,9 +30,6 @@ typedef struct {
      */
     int interlace;
 
-    /* The transparent palette index, or -1 for no transparency. */
-    int transparency;
-
     /* PRIVATE CONTEXT (set by decoder) */
 
     /* Interlace parameters */

src/libImaging/GifDecode.c

@@ -248,33 +248,27 @@ ImagingGifDecode(Imaging im, ImagingCodecState state, UINT8 *buffer, Py_ssize_t
         /* To squeeze some extra pixels out of this loop, we test for
            some common cases and handle them separately. */
 
-        /* If we have transparency, we need to use the regular loop. */
+        if (i == 1) {
-        if (context->transparency == -1) {
+            if (state->x < state->xsize - 1) {
-            if (i == 1) {
+                /* Single pixel, not at the end of the line. */
-                if (state->x < state->xsize - 1) {
+                *out++ = p[0];
-                    /* Single pixel, not at the end of the line. */
+                state->x++;
-                    *out++ = p[0];
-                    state->x++;
-                    continue;
-                }
-            } else if (state->x + i <= state->xsize) {
-                /* This string fits into current line. */
-                memcpy(out, p, i);
-                out += i;
-                state->x += i;
-                if (state->x == state->xsize) {
-                    NEWLINE(state, context);
-                }
                 continue;
             }
+        } else if (state->x + i <= state->xsize) {
+            /* This string fits into current line. */
+            memcpy(out, p, i);
+            out += i;
+            state->x += i;
+            if (state->x == state->xsize) {
+                NEWLINE(state, context);
+            }
+            continue;
         }
 
         /* No shortcut, copy pixel by pixel */
         for (c = 0; c < i; c++) {
-            if (p[c] != context->transparency) {
+            *out++ = p[c];
-                *out = p[c];
-            }
-            out++;
             if (++state->x >= state->xsize) {
                 NEWLINE(state, context);
             }