Only deprecate fromarray mode for changing data types (#9063)

Tests/test_image_array.py

@@ -101,9 +101,8 @@ def test_fromarray_strides_without_tobytes() -> None:
             self.__array_interface__ = arr_params
 
     with pytest.raises(ValueError):
-        wrapped = Wrapper({"shape": (1, 1), "strides": (1, 1)})
-        with pytest.warns(DeprecationWarning, match="'mode' parameter"):
-            Image.fromarray(wrapped, "L")
+        wrapped = Wrapper({"shape": (1, 1), "strides": (1, 1), "typestr": "|u1"})
+        Image.fromarray(wrapped, "L")
 
 
 def test_fromarray_palette() -> None:
@@ -112,9 +111,16 @@ def test_fromarray_palette() -> None:
     a = numpy.array(i)
 
     # Act
-    with pytest.warns(DeprecationWarning, match="'mode' parameter"):
-        out = Image.fromarray(a, "P")
+    out = Image.fromarray(a, "P")
 
     # Assert that the Python and C palettes match
     assert out.palette is not None
     assert len(out.palette.colors) == len(out.im.getpalette()) / 3
+
+
+def test_deprecation() -> None:
+    a = numpy.array(im.convert("L"))
+    with pytest.warns(
+        DeprecationWarning, match="'mode' parameter for changing data types"
+    ):
+        Image.fromarray(a, "1")

docs/deprecations.rst

@@ -35,8 +35,12 @@ Image.fromarray mode parameter
 
 .. deprecated:: 11.3.0
 
-The ``mode`` parameter in :py:meth:`~PIL.Image.fromarray()` has been deprecated. The
-mode can be automatically determined from the object's shape and type instead.
+Using the ``mode`` parameter in :py:meth:`~PIL.Image.fromarray()` was deprecated in
+Pillow 11.3.0. In Pillow 12.0.0, this was partially reverted, and it is now only
+deprecated when changing data types. Since pixel values do not contain information
+about palettes or color spaces, the parameter can still be used to place grayscale L
+mode data within a P mode image, or read RGB data as YCbCr for example. If omitted, the
+mode will be automatically determined from the object's shape and type.
 
 Saving I mode images as PNG
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^

docs/releasenotes/11.3.0.rst

@@ -29,6 +29,13 @@ Image.fromarray mode parameter
 The ``mode`` parameter in :py:meth:`~PIL.Image.fromarray()` has been deprecated. The
 mode can be automatically determined from the object's shape and type instead.
 
+.. note::
+
+    Since pixel values do not contain information about palettes or color spaces, part
+    of this functionality was restored in Pillow 12.0.0. The parameter can be used to
+    place grayscale L mode data within a P mode image, or read RGB data as YCbCr for
+    example.
+
 Saving I mode images as PNG
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

docs/releasenotes/12.0.0.rst

@@ -157,6 +157,15 @@ of 3.14.0 final (2025-10-07, :pep:`745`).
 
 Pillow 12.0.0 now officially supports Python 3.14.
 
+Image.fromarray mode parameter
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In Pillow 11.3.0, the ``mode`` parameter in :py:meth:`~PIL.Image.fromarray()` was
+deprecated. Part of this functionality has been restored in Pillow 12.0.0. Since pixel
+values do not contain information about palettes or color spaces, the parameter can be
+used to place grayscale L mode data within a P mode image, or read RGB data as YCbCr
+for example.
+
 ImageMorph operations must have length 1
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

src/PIL/Image.py

@@ -3259,19 +3259,10 @@ def fromarray(obj: SupportsArrayInterface, mode: str | None = None) -> Image:
     transferred. This means that P and PA mode images will lose their palette.
 
     :param obj: Object with array interface
-    :param mode: Optional mode to use when reading ``obj``. Will be determined from
-      type if ``None``. Deprecated.
-
-      This will not be used to convert the data after reading, but will be used to
-      change how the data is read::
-
-        from PIL import Image
-        import numpy as np
-        a = np.full((1, 1), 300)
-        im = Image.fromarray(a, mode="L")
-        im.getpixel((0, 0))  # 44
-        im = Image.fromarray(a, mode="RGB")
-        im.getpixel((0, 0))  # (44, 1, 0)
+    :param mode: Optional mode to use when reading ``obj``. Since pixel values do not
+      contain information about palettes or color spaces, this can be used to place
+      grayscale L mode data within a P mode image, or read RGB data as YCbCr for
+      example.
 
       See: :ref:`concept-modes` for general information about modes.
     :returns: An image object.
@@ -3282,21 +3273,28 @@ def fromarray(obj: SupportsArrayInterface, mode: str | None = None) -> Image:
     shape = arr["shape"]
     ndim = len(shape)
     strides = arr.get("strides", None)
-    if mode is None:
-        try:
-            typekey = (1, 1) + shape[2:], arr["typestr"]
-        except KeyError as e:
+    try:
+        typekey = (1, 1) + shape[2:], arr["typestr"]
+    except KeyError as e:
+        if mode is not None:
+            typekey = None
+            color_modes: list[str] = []
+        else:
             msg = "Cannot handle this data type"
             raise TypeError(msg) from e
+    if typekey is not None:
         try:
-            mode, rawmode = _fromarray_typemap[typekey]
+            typemode, rawmode, color_modes = _fromarray_typemap[typekey]
         except KeyError as e:
             typekey_shape, typestr = typekey
             msg = f"Cannot handle this data type: {typekey_shape}, {typestr}"
             raise TypeError(msg) from e
-    else:
-        deprecate("'mode' parameter", 13)
+    if mode is not None:
+        if mode != typemode and mode not in color_modes:
+            deprecate("'mode' parameter for changing data types", 13)
         rawmode = mode
+    else:
+        mode = typemode
     if mode in ["1", "L", "I", "P", "F"]:
         ndmax = 2
     elif mode == "RGB":
@@ -3393,29 +3391,29 @@ def fromqpixmap(im: ImageQt.QPixmap) -> ImageFile.ImageFile:
 
 
 _fromarray_typemap = {
-    # (shape, typestr) => mode, rawmode
+    # (shape, typestr) => mode, rawmode, color modes
     # first two members of shape are set to one
-    ((1, 1), "|b1"): ("1", "1;8"),
-    ((1, 1), "|u1"): ("L", "L"),
-    ((1, 1), "|i1"): ("I", "I;8"),
-    ((1, 1), "<u2"): ("I", "I;16"),
-    ((1, 1), ">u2"): ("I", "I;16B"),
-    ((1, 1), "<i2"): ("I", "I;16S"),
-    ((1, 1), ">i2"): ("I", "I;16BS"),
-    ((1, 1), "<u4"): ("I", "I;32"),
-    ((1, 1), ">u4"): ("I", "I;32B"),
-    ((1, 1), "<i4"): ("I", "I;32S"),
-    ((1, 1), ">i4"): ("I", "I;32BS"),
-    ((1, 1), "<f4"): ("F", "F;32F"),
-    ((1, 1), ">f4"): ("F", "F;32BF"),
-    ((1, 1), "<f8"): ("F", "F;64F"),
-    ((1, 1), ">f8"): ("F", "F;64BF"),
-    ((1, 1, 2), "|u1"): ("LA", "LA"),
-    ((1, 1, 3), "|u1"): ("RGB", "RGB"),
-    ((1, 1, 4), "|u1"): ("RGBA", "RGBA"),
+    ((1, 1), "|b1"): ("1", "1;8", []),
+    ((1, 1), "|u1"): ("L", "L", ["P"]),
+    ((1, 1), "|i1"): ("I", "I;8", []),
+    ((1, 1), "<u2"): ("I", "I;16", []),
+    ((1, 1), ">u2"): ("I", "I;16B", []),
+    ((1, 1), "<i2"): ("I", "I;16S", []),
+    ((1, 1), ">i2"): ("I", "I;16BS", []),
+    ((1, 1), "<u4"): ("I", "I;32", []),
+    ((1, 1), ">u4"): ("I", "I;32B", []),
+    ((1, 1), "<i4"): ("I", "I;32S", []),
+    ((1, 1), ">i4"): ("I", "I;32BS", []),
+    ((1, 1), "<f4"): ("F", "F;32F", []),
+    ((1, 1), ">f4"): ("F", "F;32BF", []),
+    ((1, 1), "<f8"): ("F", "F;64F", []),
+    ((1, 1), ">f8"): ("F", "F;64BF", []),
+    ((1, 1, 2), "|u1"): ("LA", "LA", ["La", "PA"]),
+    ((1, 1, 3), "|u1"): ("RGB", "RGB", ["YCbCr", "LAB", "HSV"]),
+    ((1, 1, 4), "|u1"): ("RGBA", "RGBA", ["RGBa", "RGBX", "CMYK"]),
     # shortcuts:
-    ((1, 1), f"{_ENDIAN}i4"): ("I", "I"),
-    ((1, 1), f"{_ENDIAN}f4"): ("F", "F"),
+    ((1, 1), f"{_ENDIAN}i4"): ("I", "I", []),
+    ((1, 1), f"{_ENDIAN}f4"): ("F", "F", []),
 }