Add JPEG XL plugin via optional imagecodecs

Tests/test_file_jxl.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+import io
+
+import pytest
+
+from PIL import Image
+
+imagecodecs = pytest.importorskip("imagecodecs", reason="JPEG XL requires imagecodecs")
+
+
+def test_jxl_roundtrip() -> None:
+    im = Image.new("RGB", (24, 24), (30, 120, 200))
+    im.info["lossless"] = True
+    buf = io.BytesIO()
+    im.save(buf, format="JXL")
+    buf.seek(0)
+    assert buf.read(2) == b"\xff\x0a"  # JPEG XL codestream signature
+
+    buf.seek(0)
+    with Image.open(buf) as reloaded:
+        assert reloaded.format == "JXL"
+        assert reloaded.size == (24, 24)
+        assert reloaded.mode == "RGB"
+        assert list(reloaded.getdata()) == list(im.getdata())

src/PIL/Image.py

@@ -345,6 +345,7 @@ def getmodebands(mode: str) -> int:
     ".apng": "PngImagePlugin",
     # Less common formats (init)
     ".avif": "AvifImagePlugin",
+    ".jxl": "JxlImagePlugin",
     ".avifs": "AvifImagePlugin",
     ".blp": "BlpImagePlugin",
     ".bufr": "BufrStubImagePlugin",

src/PIL/JxlImagePlugin.py

@@ -0,0 +1,91 @@
+#
+# The Python Imaging Library.
+#
+# JPEG XL support for PIL, via the optional ``imagecodecs`` package
+# (which bundles libjxl). Without it, opening or saving .jxl files
+# raises an error, mirroring how the external pillow-jxl-plugin works.
+#
+# See the README file for information on usage and redistribution.
+#
+from __future__ import annotations
+
+import io
+from typing import IO
+
+from . import Image, ImageFile
+
+try:
+    import imagecodecs
+
+    SUPPORTED = True
+except ImportError:
+    SUPPORTED = False
+
+_CODESTREAM_MAGIC = b"\xff\x0a"
+_CONTAINER_MAGIC = b"\x00\x00\x00\x0cJXL \x0d\x0a\x87\x0a"
+
+
+def _accept(prefix: bytes) -> bool:
+    return prefix.startswith((_CODESTREAM_MAGIC, _CONTAINER_MAGIC))
+
+
+class JxlImageFile(ImageFile.ImageFile):
+    format = "JXL"
+    format_description = "JPEG XL"
+
+    def _open(self) -> None:
+        if not SUPPORTED:
+            msg = "image file could not be opened because JPEG XL support not installed"
+            raise SyntaxError(msg)
+
+        assert self.fp is not None
+        data = self.fp.read()
+        try:
+            import numpy as np
+
+            arr = np.asarray(imagecodecs.jpegxl_decode(data))
+        except Exception as e:
+            msg = "could not decode JPEG XL image"
+            raise SyntaxError(msg) from e
+
+        if arr.ndim == 2:
+            self._mode = "L"
+        elif arr.shape[2] == 3:
+            self._mode = "RGB"
+        elif arr.shape[2] == 4:
+            self._mode = "RGBA"
+        else:
+            msg = f"unsupported JPEG XL channel count: {arr.shape}"
+            raise SyntaxError(msg)
+
+        self._size = arr.shape[1], arr.shape[0]
+        # Hand the decoded pixels to Pillow's raw decoder.
+        self.fp = io.BytesIO(arr.tobytes())
+        self.tile = [ImageFile._Tile("raw", (0, 0, *self._size), 0, (self._mode, 0, 1))]
+        self._fp = self.fp
+
+
+def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
+    if not SUPPORTED:
+        msg = "JPEG XL support not installed"
+        raise ValueError(msg)
+
+    import numpy as np
+
+    if im.mode not in ("L", "RGB", "RGBA"):
+        im = im.convert("RGBA" if "A" in im.getbands() else "RGB")
+    arr = np.asarray(im)
+    lossless = bool(im.info.get("lossless", False))
+    encoded = imagecodecs.jpegxl_encode(
+        arr,
+        lossless=lossless,
+        distance=None if lossless else float(im.info.get("distance", 1.0)),
+        effort=int(im.info.get("effort", 7)),
+    )
+    fp.write(bytes(encoded))
+
+
+Image.register_open(JxlImageFile.format, JxlImageFile, _accept)
+Image.register_save(JxlImageFile.format, _save)
+Image.register_extension(JxlImageFile.format, ".jxl")
+Image.register_mime(JxlImageFile.format, "image/jxl")

src/PIL/__init__.py

@@ -26,6 +26,7 @@
 
 _plugins = [
     "AvifImagePlugin",
+    "JxlImagePlugin",
     "BlpImagePlugin",
     "BmpImagePlugin",
     "BufrStubImagePlugin",