diff --git a/src/PIL/BlpImagePlugin.py b/src/PIL/BlpImagePlugin.py
index 2db115ccc4f..003fa9b2479 100644
--- a/src/PIL/BlpImagePlugin.py
+++ b/src/PIL/BlpImagePlugin.py
@@ -31,6 +31,7 @@
 
 from __future__ import annotations
 
+import abc
 import os
 import struct
 from enum import IntEnum
@@ -276,7 +277,7 @@ def _open(self) -> None:
 class _BLPBaseDecoder(ImageFile.PyDecoder):
     _pulls_fd = True
 
-    def decode(self, buffer):
+    def decode(self, buffer: bytes) -> tuple[int, int]:
         try:
             self._read_blp_header()
             self._load()
@@ -285,6 +286,10 @@ def decode(self, buffer):
             raise OSError(msg) from e
         return -1, 0
 
+    @abc.abstractmethod
+    def _load(self) -> None:
+        pass
+
     def _read_blp_header(self) -> None:
         assert self.fd is not None
         self.fd.seek(4)
@@ -318,7 +323,7 @@ def _read_palette(self) -> list[tuple[int, int, int, int]]:
             ret.append((b, g, r, a))
         return ret
 
-    def _read_bgra(self, palette):
+    def _read_bgra(self, palette: list[tuple[int, int, int, int]]) -> bytearray:
         data = bytearray()
         _data = BytesIO(self._safe_read(self._blp_lengths[0]))
         while True:
@@ -327,7 +332,7 @@ def _read_bgra(self, palette):
             except struct.error:
                 break
             b, g, r, a = palette[offset]
-            d = (r, g, b)
+            d: tuple[int, ...] = (r, g, b)
             if self._blp_alpha_depth:
                 d += (a,)
             data.extend(d)
@@ -431,7 +436,7 @@ def _write_palette(self) -> bytes:
             data += b"\x00" * 4
         return data
 
-    def encode(self, bufsize):
+    def encode(self, bufsize: int) -> tuple[int, int, bytes]:
         palette_data = self._write_palette()
 
         offset = 20 + 16 * 4 * 2 + len(palette_data)
@@ -449,7 +454,7 @@ def encode(self, bufsize):
         return len(data), 0, data
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode != "P":
         msg = "Unsupported BLP image mode"
         raise ValueError(msg)
diff --git a/src/PIL/BmpImagePlugin.py b/src/PIL/BmpImagePlugin.py
index 2df1d8d33bd..45c1ea941e8 100644
--- a/src/PIL/BmpImagePlugin.py
+++ b/src/PIL/BmpImagePlugin.py
@@ -395,12 +395,12 @@ def _open(self) -> None:
 }
 
 
-def _dib_save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _dib_save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     _save(im, fp, filename, False)
 
 
 def _save(
-    im: Image.Image, fp: IO[bytes], filename: str, bitmap_header: bool = True
+    im: Image.Image, fp: IO[bytes], filename: str | bytes, bitmap_header: bool = True
 ) -> None:
     try:
         rawmode, bits, colors = SAVE[im.mode]
diff --git a/src/PIL/BufrStubImagePlugin.py b/src/PIL/BufrStubImagePlugin.py
index 7388a2b8a3a..0ee2f653b2c 100644
--- a/src/PIL/BufrStubImagePlugin.py
+++ b/src/PIL/BufrStubImagePlugin.py
@@ -60,7 +60,7 @@ def _load(self) -> ImageFile.StubHandler | None:
         return _handler
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "BUFR save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/DdsImagePlugin.py b/src/PIL/DdsImagePlugin.py
index a3efadb030d..861a1eca0cc 100644
--- a/src/PIL/DdsImagePlugin.py
+++ b/src/PIL/DdsImagePlugin.py
@@ -511,7 +511,7 @@ def decode(self, buffer):
         return -1, 0
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode not in ("RGB", "RGBA", "L", "LA"):
         msg = f"cannot write mode {im.mode} as DDS"
         raise OSError(msg)
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index f41bc2b321d..a540595b85b 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -715,12 +715,12 @@ def _write_multiple_frames(im, fp, palette):
     return True
 
 
-def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     _save(im, fp, filename, save_all=True)
 
 
 def _save(
-    im: Image.Image, fp: IO[bytes], filename: str, save_all: bool = False
+    im: Image.Image, fp: IO[bytes], filename: str | bytes, save_all: bool = False
 ) -> None:
     # header
     if "palette" in im.encoderinfo or "palette" in im.info:
@@ -796,7 +796,7 @@ def _write_local_header(fp, im, offset, flags):
     fp.write(o8(8))  # bits
 
 
-def _save_netpbm(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_netpbm(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     # Unused by default.
     # To use, uncomment the register_save call at the end of the file.
     #
diff --git a/src/PIL/GribStubImagePlugin.py b/src/PIL/GribStubImagePlugin.py
index d3655f4ddc0..e9aa084b281 100644
--- a/src/PIL/GribStubImagePlugin.py
+++ b/src/PIL/GribStubImagePlugin.py
@@ -60,7 +60,7 @@ def _load(self) -> ImageFile.StubHandler | None:
         return _handler
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "GRIB save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/Hdf5StubImagePlugin.py b/src/PIL/Hdf5StubImagePlugin.py
index b789c215fee..cc9e73deb80 100644
--- a/src/PIL/Hdf5StubImagePlugin.py
+++ b/src/PIL/Hdf5StubImagePlugin.py
@@ -60,7 +60,7 @@ def _load(self) -> ImageFile.StubHandler | None:
         return _handler
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "HDF5 save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/IcnsImagePlugin.py b/src/PIL/IcnsImagePlugin.py
index 0a86ba883f1..2a89d498cbf 100644
--- a/src/PIL/IcnsImagePlugin.py
+++ b/src/PIL/IcnsImagePlugin.py
@@ -22,6 +22,7 @@
 import os
 import struct
 import sys
+from typing import IO
 
 from . import Image, ImageFile, PngImagePlugin, features
 
@@ -312,7 +313,7 @@ def load(self):
         return px
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     """
     Saves the image as a series of PNG files,
     that are then combined into a .icns file.
@@ -346,29 +347,27 @@ def _save(im, fp, filename):
     entries = []
     for type, size in sizes.items():
         stream = size_streams[size]
-        entries.append(
-            {"type": type, "size": HEADERSIZE + len(stream), "stream": stream}
-        )
+        entries.append((type, HEADERSIZE + len(stream), stream))
 
     # Header
     fp.write(MAGIC)
     file_length = HEADERSIZE  # Header
     file_length += HEADERSIZE + 8 * len(entries)  # TOC
-    file_length += sum(entry["size"] for entry in entries)
+    file_length += sum(entry[1] for entry in entries)
     fp.write(struct.pack(">i", file_length))
 
     # TOC
     fp.write(b"TOC ")
     fp.write(struct.pack(">i", HEADERSIZE + len(entries) * HEADERSIZE))
     for entry in entries:
-        fp.write(entry["type"])
-        fp.write(struct.pack(">i", entry["size"]))
+        fp.write(entry[0])
+        fp.write(struct.pack(">i", entry[1]))
 
     # Data
     for entry in entries:
-        fp.write(entry["type"])
-        fp.write(struct.pack(">i", entry["size"]))
-        fp.write(entry["stream"])
+        fp.write(entry[0])
+        fp.write(struct.pack(">i", entry[1]))
+        fp.write(entry[2])
 
     if hasattr(fp, "flush"):
         fp.flush()
diff --git a/src/PIL/IcoImagePlugin.py b/src/PIL/IcoImagePlugin.py
index af94e5a2e7f..227fcf35cbb 100644
--- a/src/PIL/IcoImagePlugin.py
+++ b/src/PIL/IcoImagePlugin.py
@@ -40,7 +40,7 @@
 _MAGIC = b"\0\0\1\0"
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     fp.write(_MAGIC)  # (2+2)
     bmp = im.encoderinfo.get("bitmap_format") == "bmp"
     sizes = im.encoderinfo.get(
diff --git a/src/PIL/ImImagePlugin.py b/src/PIL/ImImagePlugin.py
index c98cfb0984b..015c2febea8 100644
--- a/src/PIL/ImImagePlugin.py
+++ b/src/PIL/ImImagePlugin.py
@@ -326,7 +326,7 @@ def tell(self) -> int:
 }
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     try:
         image_type, rawmode = SAVE[im.mode]
     except KeyError as e:
@@ -341,6 +341,8 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
         # or: SyntaxError("not an IM file")
         # 8 characters are used for "Name: " and "\r\n"
         # Keep just the filename, ditch the potentially overlong path
+        if isinstance(filename, bytes):
+            filename = filename.decode("ascii")
         name, ext = os.path.splitext(os.path.basename(filename))
         name = "".join([name[: 92 - len(ext)], ext])
 
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index f6ffac8a77f..af174861019 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -626,7 +626,7 @@ def _ensure_mutable(self) -> None:
             self.load()
 
     def _dump(
-        self, file: str | None = None, format: str | None = None, **options
+        self, file: str | None = None, format: str | None = None, **options: Any
     ) -> str:
         suffix = ""
         if format:
@@ -649,10 +649,12 @@ def _dump(
 
         return filename
 
-    def __eq__(self, other):
+    def __eq__(self, other: object) -> bool:
+        if self.__class__ is not other.__class__:
+            return False
+        assert isinstance(other, Image)
         return (
-            self.__class__ is other.__class__
-            and self.mode == other.mode
+            self.mode == other.mode
             and self.size == other.size
             and self.info == other.info
             and self.getpalette() == other.getpalette()
@@ -2965,7 +2967,7 @@ def transform(
 # Debugging
 
 
-def _wedge():
+def _wedge() -> Image:
     """Create grayscale wedge (for debugging only)"""
 
     return Image()._new(core.wedge("L"))
@@ -3566,7 +3568,9 @@ def register_mime(id: str, mimetype: str) -> None:
     MIME[id.upper()] = mimetype
 
 
-def register_save(id: str, driver) -> None:
+def register_save(
+    id: str, driver: Callable[[Image, IO[bytes], str | bytes], None]
+) -> None:
     """
     Registers an image save function.  This function should not be
     used in application code.
@@ -3577,7 +3581,9 @@ def register_save(id: str, driver) -> None:
     SAVE[id.upper()] = driver
 
 
-def register_save_all(id: str, driver) -> None:
+def register_save_all(
+    id: str, driver: Callable[[Image, IO[bytes], str | bytes], None]
+) -> None:
     """
     Registers an image function to save all the frames
     of a multiframe format.  This function should not be
@@ -3651,7 +3657,7 @@ def register_encoder(name: str, encoder: type[ImageFile.PyEncoder]) -> None:
 # Simple display support.
 
 
-def _show(image, **options) -> None:
+def _show(image: Image, **options: Any) -> None:
     from . import ImageShow
 
     ImageShow.show(image, **options)
@@ -3661,7 +3667,9 @@ def _show(image, **options) -> None:
 # Effects
 
 
-def effect_mandelbrot(size, extent, quality):
+def effect_mandelbrot(
+    size: tuple[int, int], extent: tuple[int, int, int, int], quality: int
+) -> Image:
     """
     Generate a Mandelbrot set covering the given extent.
 
diff --git a/src/PIL/ImageDraw.py b/src/PIL/ImageDraw.py
index 73ed3d4a9a6..01f99c11984 100644
--- a/src/PIL/ImageDraw.py
+++ b/src/PIL/ImageDraw.py
@@ -219,7 +219,9 @@ def line(self, xy: Coords, fill=None, width=0, joint=None) -> None:
                         # This is a straight line, so no joint is required
                         continue
 
-                    def coord_at_angle(coord, angle):
+                    def coord_at_angle(
+                        coord: Sequence[float], angle: float
+                    ) -> tuple[float, float]:
                         x, y = coord
                         angle -= 90
                         distance = width / 2 - 1
@@ -1109,11 +1111,13 @@ def _get_angles(n_sides: int, rotation: float) -> list[float]:
     return [_compute_polygon_vertex(angle) for angle in angles]
 
 
-def _color_diff(color1, color2: float | tuple[int, ...]) -> float:
+def _color_diff(
+    color1: float | tuple[int, ...], color2: float | tuple[int, ...]
+) -> float:
     """
     Uses 1-norm distance to calculate difference between two values.
     """
-    if isinstance(color2, tuple):
-        return sum(abs(color1[i] - color2[i]) for i in range(0, len(color2)))
-    else:
-        return abs(color1 - color2)
+    first = color1 if isinstance(color1, tuple) else (color1,)
+    second = color2 if isinstance(color2, tuple) else (color2,)
+
+    return sum(abs(first[i] - second[i]) for i in range(0, len(second)))
diff --git a/src/PIL/ImageFile.py b/src/PIL/ImageFile.py
index f0e49238760..6bef681e979 100644
--- a/src/PIL/ImageFile.py
+++ b/src/PIL/ImageFile.py
@@ -763,7 +763,7 @@ class PyEncoder(PyCodec):
     def pushes_fd(self):
         return self._pushes_fd
 
-    def encode(self, bufsize):
+    def encode(self, bufsize: int) -> tuple[int, int, bytes]:
         """
         Override to perform the encoding process.
 
diff --git a/src/PIL/Jpeg2KImagePlugin.py b/src/PIL/Jpeg2KImagePlugin.py
index 5a0ef0d01a3..72c2cb85e3c 100644
--- a/src/PIL/Jpeg2KImagePlugin.py
+++ b/src/PIL/Jpeg2KImagePlugin.py
@@ -329,11 +329,13 @@ def _accept(prefix: bytes) -> bool:
 # Save support
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     # Get the keyword arguments
     info = im.encoderinfo
 
-    if filename.endswith(".j2k") or info.get("no_jp2", False):
+    if isinstance(filename, str):
+        filename = filename.encode()
+    if filename.endswith(b".j2k") or info.get("no_jp2", False):
         kind = "j2k"
     else:
         kind = "jp2"
diff --git a/src/PIL/JpegImagePlugin.py b/src/PIL/JpegImagePlugin.py
index 4d0b75e77ed..0c8a678887e 100644
--- a/src/PIL/JpegImagePlugin.py
+++ b/src/PIL/JpegImagePlugin.py
@@ -42,7 +42,7 @@
 import sys
 import tempfile
 import warnings
-from typing import Any
+from typing import IO, Any
 
 from . import Image, ImageFile
 from ._binary import i16be as i16
@@ -644,7 +644,7 @@ def get_sampling(im):
     return samplings.get(sampling, -1)
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.width == 0 or im.height == 0:
         msg = "cannot write empty image as JPEG"
         raise ValueError(msg)
@@ -827,7 +827,7 @@ def validate_qtables(qtables):
     ImageFile._save(im, fp, [("jpeg", (0, 0) + im.size, 0, rawmode)], bufsize)
 
 
-def _save_cjpeg(im, fp, filename):
+def _save_cjpeg(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     # ALTERNATIVE: handle JPEGs via the IJG command line utilities.
     tempfile = im._dump()
     subprocess.check_call(["cjpeg", "-outfile", filename, tempfile])
diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index 6716722f204..152e19e2365 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -33,7 +33,7 @@
 from ._binary import o32le
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     JpegImagePlugin._save(im, fp, filename)
 
 
diff --git a/src/PIL/MspImagePlugin.py b/src/PIL/MspImagePlugin.py
index 65cc70624b7..0a75c868b97 100644
--- a/src/PIL/MspImagePlugin.py
+++ b/src/PIL/MspImagePlugin.py
@@ -164,7 +164,7 @@ def decode(self, buffer: bytes) -> tuple[int, int]:
 # write MSP files (uncompressed only)
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode != "1":
         msg = f"cannot write mode {im.mode} as MSP"
         raise OSError(msg)
diff --git a/src/PIL/PcxImagePlugin.py b/src/PIL/PcxImagePlugin.py
index 026bfd9a01b..dd42003b5a3 100644
--- a/src/PIL/PcxImagePlugin.py
+++ b/src/PIL/PcxImagePlugin.py
@@ -144,7 +144,7 @@ def _open(self) -> None:
 }
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     try:
         version, bits, planes, rawmode = SAVE[im.mode]
     except KeyError as e:
diff --git a/src/PIL/PdfImagePlugin.py b/src/PIL/PdfImagePlugin.py
index ccd28f3434b..f0da1e04797 100644
--- a/src/PIL/PdfImagePlugin.py
+++ b/src/PIL/PdfImagePlugin.py
@@ -40,7 +40,7 @@
 #  5. page contents
 
 
-def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     _save(im, fp, filename, save_all=True)
 
 
diff --git a/src/PIL/PdfParser.py b/src/PIL/PdfParser.py
index a6c24e67179..52e8358017a 100644
--- a/src/PIL/PdfParser.py
+++ b/src/PIL/PdfParser.py
@@ -76,7 +76,7 @@ class PdfFormatError(RuntimeError):
     pass
 
 
-def check_format_condition(condition, error_message):
+def check_format_condition(condition: bool, error_message: str) -> None:
     if not condition:
         raise PdfFormatError(error_message)
 
@@ -93,12 +93,11 @@ def __str__(self) -> str:
     def __bytes__(self) -> bytes:
         return self.__str__().encode("us-ascii")
 
-    def __eq__(self, other):
-        return (
-            other.__class__ is self.__class__
-            and other.object_id == self.object_id
-            and other.generation == self.generation
-        )
+    def __eq__(self, other: object) -> bool:
+        if self.__class__ is not other.__class__:
+            return False
+        assert isinstance(other, IndirectReference)
+        return other.object_id == self.object_id and other.generation == self.generation
 
     def __ne__(self, other):
         return not (self == other)
diff --git a/src/PIL/PngImagePlugin.py b/src/PIL/PngImagePlugin.py
index 76ffdef3f55..9aaadb47d5e 100644
--- a/src/PIL/PngImagePlugin.py
+++ b/src/PIL/PngImagePlugin.py
@@ -1234,7 +1234,7 @@ def _write_multiple_frames(im, fp, chunk, rawmode, default_image, append_images)
             seq_num = fdat_chunks.seq_num
 
 
-def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     _save(im, fp, filename, save_all=True)
 
 
diff --git a/src/PIL/PpmImagePlugin.py b/src/PIL/PpmImagePlugin.py
index 94bf430b825..16c9ccbba72 100644
--- a/src/PIL/PpmImagePlugin.py
+++ b/src/PIL/PpmImagePlugin.py
@@ -328,7 +328,7 @@ def decode(self, buffer: bytes) -> tuple[int, int]:
 # --------------------------------------------------------------------
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode == "1":
         rawmode, head = "1;I", b"P4"
     elif im.mode == "L":
diff --git a/src/PIL/QoiImagePlugin.py b/src/PIL/QoiImagePlugin.py
index f2cf06d0dd7..202ef52d09b 100644
--- a/src/PIL/QoiImagePlugin.py
+++ b/src/PIL/QoiImagePlugin.py
@@ -37,6 +37,8 @@ def _open(self) -> None:
 
 class QoiDecoder(ImageFile.PyDecoder):
     _pulls_fd = True
+    _previous_pixel: bytes | bytearray | None = None
+    _previously_seen_pixels: dict[int, bytes | bytearray] = {}
 
     def _add_to_previous_pixels(self, value: bytes | bytearray) -> None:
         self._previous_pixel = value
@@ -45,9 +47,10 @@ def _add_to_previous_pixels(self, value: bytes | bytearray) -> None:
         hash_value = (r * 3 + g * 5 + b * 7 + a * 11) % 64
         self._previously_seen_pixels[hash_value] = value
 
-    def decode(self, buffer):
+    def decode(self, buffer: bytes) -> tuple[int, int]:
+        assert self.fd is not None
+
         self._previously_seen_pixels = {}
-        self._previous_pixel = None
         self._add_to_previous_pixels(bytearray((0, 0, 0, 255)))
 
         data = bytearray()
@@ -55,7 +58,8 @@ def decode(self, buffer):
         dest_length = self.state.xsize * self.state.ysize * bands
         while len(data) < dest_length:
             byte = self.fd.read(1)[0]
-            if byte == 0b11111110:  # QOI_OP_RGB
+            value: bytes | bytearray
+            if byte == 0b11111110 and self._previous_pixel:  # QOI_OP_RGB
                 value = bytearray(self.fd.read(3)) + self._previous_pixel[3:]
             elif byte == 0b11111111:  # QOI_OP_RGBA
                 value = self.fd.read(4)
@@ -66,7 +70,7 @@ def decode(self, buffer):
                     value = self._previously_seen_pixels.get(
                         op_index, bytearray((0, 0, 0, 0))
                     )
-                elif op == 1:  # QOI_OP_DIFF
+                elif op == 1 and self._previous_pixel:  # QOI_OP_DIFF
                     value = bytearray(
                         (
                             (self._previous_pixel[0] + ((byte & 0b00110000) >> 4) - 2)
@@ -77,7 +81,7 @@ def decode(self, buffer):
                             self._previous_pixel[3],
                         )
                     )
-                elif op == 2:  # QOI_OP_LUMA
+                elif op == 2 and self._previous_pixel:  # QOI_OP_LUMA
                     second_byte = self.fd.read(1)[0]
                     diff_green = (byte & 0b00111111) - 32
                     diff_red = ((second_byte & 0b11110000) >> 4) - 8
@@ -90,7 +94,7 @@ def decode(self, buffer):
                         )
                     )
                     value += self._previous_pixel[3:]
-                elif op == 3:  # QOI_OP_RUN
+                elif op == 3 and self._previous_pixel:  # QOI_OP_RUN
                     run_length = (byte & 0b00111111) + 1
                     value = self._previous_pixel
                     if bands == 3:
diff --git a/src/PIL/SgiImagePlugin.py b/src/PIL/SgiImagePlugin.py
index 7bd84ebd491..50d97910932 100644
--- a/src/PIL/SgiImagePlugin.py
+++ b/src/PIL/SgiImagePlugin.py
@@ -125,7 +125,7 @@ def _open(self) -> None:
             ]
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode not in {"RGB", "RGBA", "L"}:
         msg = "Unsupported SGI image mode"
         raise ValueError(msg)
@@ -171,8 +171,9 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     # Maximum Byte value (255 = 8bits per pixel)
     pinmax = 255
     # Image name (79 characters max, truncated below in write)
-    filename = os.path.basename(filename)
-    img_name = os.path.splitext(filename)[0].encode("ascii", "ignore")
+    img_name = os.path.splitext(os.path.basename(filename))[0]
+    if isinstance(img_name, str):
+        img_name = img_name.encode("ascii", "ignore")
     # Standard representation of pixel in the file
     colormap = 0
     fp.write(struct.pack(">h", magic_number))
diff --git a/src/PIL/SpiderImagePlugin.py b/src/PIL/SpiderImagePlugin.py
index 98dd91c0e24..a6cc00019da 100644
--- a/src/PIL/SpiderImagePlugin.py
+++ b/src/PIL/SpiderImagePlugin.py
@@ -263,7 +263,7 @@ def makeSpiderHeader(im: Image.Image) -> list[bytes]:
     return [struct.pack("f", v) for v in hdr]
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode[0] != "F":
         im = im.convert("F")
 
@@ -279,9 +279,10 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     ImageFile._save(im, fp, [("raw", (0, 0) + im.size, 0, (rawmode, 0, 1))])
 
 
-def _save_spider(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_spider(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     # get the filename extension and register it with Image
-    ext = os.path.splitext(filename)[1]
+    filename_ext = os.path.splitext(filename)[1]
+    ext = filename_ext.decode() if isinstance(filename_ext, bytes) else filename_ext
     Image.register_extension(SpiderImageFile.format, ext)
     _save(im, fp, filename)
 
diff --git a/src/PIL/TgaImagePlugin.py b/src/PIL/TgaImagePlugin.py
index 401a83f9fba..f16f075df05 100644
--- a/src/PIL/TgaImagePlugin.py
+++ b/src/PIL/TgaImagePlugin.py
@@ -178,7 +178,7 @@ def load_end(self) -> None:
 }
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     try:
         rawmode, bits, colormaptype, imagetype = SAVE[im.mode]
     except KeyError as e:
diff --git a/src/PIL/TiffImagePlugin.py b/src/PIL/TiffImagePlugin.py
index 0b96017552a..08ee506b162 100644
--- a/src/PIL/TiffImagePlugin.py
+++ b/src/PIL/TiffImagePlugin.py
@@ -387,7 +387,7 @@ def __repr__(self) -> str:
     def __hash__(self):
         return self._val.__hash__()
 
-    def __eq__(self, other):
+    def __eq__(self, other: object) -> bool:
         val = self._val
         if isinstance(other, IFDRational):
             other = other._val
@@ -2149,7 +2149,7 @@ def fixOffsets(self, count, isShort=False, isLong=False):
                 self.rewriteLastLong(offset)
 
 
-def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     encoderinfo = im.encoderinfo.copy()
     encoderconfig = im.encoderconfig
     append_images = list(encoderinfo.get("append_images", []))
diff --git a/src/PIL/WebPImagePlugin.py b/src/PIL/WebPImagePlugin.py
index 463d6a62398..97debc2edc9 100644
--- a/src/PIL/WebPImagePlugin.py
+++ b/src/PIL/WebPImagePlugin.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from io import BytesIO
-from typing import Any
+from typing import IO, Any
 
 from . import Image, ImageFile
 
@@ -182,7 +182,7 @@ def tell(self) -> int:
         return self.__logical_frame
 
 
-def _save_all(im, fp, filename):
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     encoderinfo = im.encoderinfo.copy()
     append_images = list(encoderinfo.get("append_images", []))
 
@@ -195,7 +195,7 @@ def _save_all(im, fp, filename):
         _save(im, fp, filename)
         return
 
-    background = (0, 0, 0, 0)
+    background: int | tuple[int, ...] = (0, 0, 0, 0)
     if "background" in encoderinfo:
         background = encoderinfo["background"]
     elif "background" in im.info:
@@ -325,7 +325,7 @@ def _save_all(im, fp, filename):
     fp.write(data)
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     lossless = im.encoderinfo.get("lossless", False)
     quality = im.encoderinfo.get("quality", 80)
     alpha_quality = im.encoderinfo.get("alpha_quality", 100)
diff --git a/src/PIL/WmfImagePlugin.py b/src/PIL/WmfImagePlugin.py
index a68f705a03c..3d5cddcc8f5 100644
--- a/src/PIL/WmfImagePlugin.py
+++ b/src/PIL/WmfImagePlugin.py
@@ -163,7 +163,7 @@ def load(self, dpi=None):
         return super().load()
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "WMF save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/XbmImagePlugin.py b/src/PIL/XbmImagePlugin.py
index eee7274361c..6d11bbfcf6b 100644
--- a/src/PIL/XbmImagePlugin.py
+++ b/src/PIL/XbmImagePlugin.py
@@ -70,7 +70,7 @@ def _open(self) -> None:
         self.tile = [("xbm", (0, 0) + self.size, m.end(), None)]
 
 
-def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     if im.mode != "1":
         msg = f"cannot write mode {im.mode} as XBM"
         raise OSError(msg)