fix: Improve edge transparency handling by modifying only the Alpha channel

In our testing, the method of exclusively processing the Alpha channel yielded the best results. This approach focuses on adjusting transparency while preserving the RGB color information, which prevents color distortion and maintains image detail. Key reasons for the improvement include:

- Protecting RGB from color alterations, avoiding color seepage and contamination.
- Precisely removing unwanted semi-transparency in the Alpha channel, eliminating white edges.
- Simplifying the process, reducing complexity, and minimizing risk of introducing new issues.

By targeting transparency issues directly in the Alpha channel, we achieve cleaner edges without compromising the image's color quality and detail.

sticker/lib/util.py

@@ -15,6 +15,7 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 from functools import partial
 from io import BytesIO
+import numpy as np
 import os.path
 import subprocess
 import json
@@ -26,7 +27,7 @@ try:
 except ImportError:
     print("[Warning] Magic is not installed, using file extensions to guess mime types")
     magic = None
-from PIL import Image, ImageSequence
+from PIL import Image, ImageSequence, ImageFilter
 
 from . import matrix
 
@@ -48,7 +49,7 @@ def guess_mime(data: bytes) -> str:
     return mime or "image/png"
 
 
-def video_to_webp(data: bytes) -> bytes:
+def _video_to_webp(data: bytes) -> bytes:
     mime = guess_mime(data)
     ext = mimetypes.guess_extension(mime)
     with tempfile.NamedTemporaryFile(suffix=ext) as video:
@@ -74,9 +75,9 @@ def video_to_webp(data: bytes) -> bytes:
             return webp.read()
 
 
-def video_to_gif(data: bytes, mime: str) -> bytes:
+def video_to_webp(data: bytes) -> bytes:
+    mime = guess_mime(data)
     ext = mimetypes.guess_extension(mime)
-    if mime.startswith("video/"):
     # run ffmpeg to fix duration
     with tempfile.NamedTemporaryFile(suffix=ext) as temp:
         temp.write(data)
@@ -89,17 +90,87 @@ def video_to_gif(data: bytes, mime: str) -> bytes:
                 raise RuntimeError(f"Run ffmpeg failed with code {result.returncode}, Error occurred:\n{result.stderr}")
             temp_fixed.seek(0)
             data = temp_fixed.read()
-    data = video_to_webp(data)
-    with tempfile.NamedTemporaryFile(suffix=ext) as temp:
-        temp.write(data)
-        temp.flush()
-        with tempfile.NamedTemporaryFile(suffix=".gif") as gif:
+    return _video_to_webp(data)
+
+
+def process_frame(frame):
+    """
+    Process GIF frame, repair edges, ensure no white or semi-transparent pixels, while keeping color information intact.
+    """
+    frame = frame.convert('RGBA')
+
+    # Decompose Alpha channel
+    alpha = frame.getchannel('A')
+
+    # Process Alpha channel with threshold, remove semi-transparent pixels
+    # Threshold can be adjusted as needed (0-255), 128 is the middle value
+    threshold = 128
+    alpha = alpha.point(lambda x: 255 if x >= threshold else 0)
+
+    # Process Alpha channel with MinFilter, remove edge noise
+    alpha = alpha.filter(ImageFilter.MinFilter(3))
+
+    # Process Alpha channel with MaxFilter, repair edges
+    alpha = alpha.filter(ImageFilter.MaxFilter(3))
+
+    # Apply processed Alpha channel back to image
+    frame.putalpha(alpha)
+
+    return frame
+
+
+def webp_to_others(data: bytes, mimetype: str) -> bytes:
+    with tempfile.NamedTemporaryFile(suffix=".webp") as webp:
+        webp.write(data)
+        webp.flush()
+        ext = mimetypes.guess_extension(mimetype)
+        with tempfile.NamedTemporaryFile(suffix=ext) as img:
             print(".", end="", flush=True)
-            im = Image.open(temp.name)
+            im = Image.open(webp.name)
             im.info.pop('background', None)
-            im.save(gif.name, save_all=True, lossless=True, quality=100, method=6)
-            gif.seek(0)
-            return gif.read()
+
+            if mimetype == "image/gif":
+                frames = []
+                duration = []
+
+                for frame in ImageSequence.Iterator(im):
+                    frame = process_frame(frame)
+                    frames.append(frame)
+                    duration.append(frame.info.get('duration', 100))
+
+                frames[0].save(img.name, save_all=True, lossless=True, quality=100, method=6,
+                               append_images=frames[1:], loop=0, duration=duration, disposal=2)
+            else:
+                im.save(img.name, save_all=True, lossless=True, quality=100, method=6)
+
+            img.seek(0)
+            return img.read()
+
+
+def is_uniform_animated_webp(data: bytes) -> bool:
+    img = Image.open(BytesIO(data))
+    if img.n_frames <= 1:
+        return False
+
+    first_frame = np.array(img)
+    for frame_number in range(1, img.n_frames):
+        img.seek(frame_number)
+        current_frame = np.array(img)
+        if not np.array_equal(first_frame, current_frame):
+            return False
+
+    return True
+
+
+def webp_to_gif_or_png(data: bytes) -> bytes:
+    # check if the webp is animated
+    image: Image.Image = Image.open(BytesIO(data))
+    is_animated = getattr(image, "is_animated", False)
+    if is_animated and not is_uniform_animated_webp(data):
+        return webp_to_others(data, "image/gif")
+    else:
+        # convert to png
+        return webp_to_others(data, "image/png")
 
 
 def opermize_gif(data: bytes) -> bytes:
@@ -118,9 +189,6 @@ def opermize_gif(data: bytes) -> bytes:
 def _convert_image(data: bytes, mimetype: str) -> (bytes, int, int):
     image: Image.Image = Image.open(BytesIO(data))
     new_file = BytesIO()
-    suffix = mimetypes.guess_extension(mimetype)
-    if suffix:
-        suffix = suffix[1:]
     # Determine if the image is a GIF
     is_animated = getattr(image, "is_animated", False)
     if is_animated:
@@ -138,6 +206,9 @@ def _convert_image(data: bytes, mimetype: str) -> (bytes, int, int):
         # Get the size of the first frame to determine resizing
         w, h = frames[0].size
     else:
+        suffix = mimetypes.guess_extension(mimetype)
+        if suffix:
+            suffix = suffix[1:]
         image = image.convert("RGBA")
         image.save(new_file, format=suffix)
         w, h = image.size
@@ -155,9 +226,8 @@ def _convert_image(data: bytes, mimetype: str) -> (bytes, int, int):
 def _convert_sticker(data: bytes) -> (bytes, str, int, int):
     mimetype = guess_mime(data)
     if mimetype.startswith("video/"):
-        data = video_to_gif(data, mimetype)
+        data = video_to_webp(data)
         print(".", end="", flush=True)
-        mimetype = "image/gif"
     elif mimetype.startswith("application/gzip"):
         print(".", end="", flush=True)
         # unzip file
@@ -168,7 +238,7 @@ def _convert_sticker(data: bytes) -> (bytes, str, int, int):
             suffix = mimetypes.guess_extension(mimetype)
             with tempfile.NamedTemporaryFile(suffix=suffix) as temp:
                 temp.write(data)
-                with tempfile.NamedTemporaryFile(suffix=".gif") as gif:
+                with tempfile.NamedTemporaryFile(suffix=".webp") as gif:
                     # run lottie_convert.py input output
                     print(".", end="", flush=True)
                     import subprocess
@@ -179,7 +249,10 @@ def _convert_sticker(data: bytes) -> (bytes, str, int, int):
                         raise RuntimeError(f"Run {cmd} failed with code {retcode}, Error occurred:\n{result.stderr}")
                     gif.seek(0)
                     data = gif.read()
-                    mimetype = "image/gif"
+    mimetype = guess_mime(data)
+    if mimetype == "image/webp":
+        data = webp_to_gif_or_png(data)
+        mimetype = guess_mime(data)
     rlt = _convert_image(data, mimetype)
     data = rlt[0]
     if mimetype == "image/gif":