diff --git a/.ci/install.sh b/.ci/install.sh
index d5cbd82488b..4748feb3d49 100755
--- a/.ci/install.sh
+++ b/.ci/install.sh
@@ -23,7 +23,7 @@ if [[ $(uname) != CYGWIN* ]]; then
     sudo apt-get -qq install libfreetype6-dev liblcms2-dev python3-tk\
                              ghostscript libffi-dev libjpeg-turbo-progs libopenjp2-7-dev\
                              cmake meson imagemagick libharfbuzz-dev libfribidi-dev\
-                             sway wl-clipboard
+                             sway wl-clipboard libopenblas-dev
 fi
 
 python3 -m pip install --upgrade pip
@@ -38,8 +38,7 @@ python3 -m pip install -U pytest-timeout
 python3 -m pip install pyroma
 
 if [[ $(uname) != CYGWIN* ]]; then
-    # TODO Remove condition when NumPy supports 3.12
-    if ! [ "$GHA_PYTHON_VERSION" == "3.12-dev" ]; then python3 -m pip install numpy ; fi
+    python3 -m pip install numpy
 
     # PyQt6 doesn't support PyPy3
     if [[ $GHA_PYTHON_VERSION == 3.* ]]; then
diff --git a/.github/workflows/macos-install.sh b/.github/workflows/macos-install.sh
index 1fc6262f4fe..a20838a1507 100755
--- a/.github/workflows/macos-install.sh
+++ b/.github/workflows/macos-install.sh
@@ -3,6 +3,7 @@
 set -e
 
 brew install libtiff libjpeg openjpeg libimagequant webp little-cms2 freetype libraqm
+export PKG_CONFIG_PATH="/usr/local/opt/openblas/lib/pkgconfig"
 
 PYTHONOPTIMIZE=0 python3 -m pip install cffi
 python3 -m pip install coverage
@@ -13,8 +14,7 @@ python3 -m pip install -U pytest-cov
 python3 -m pip install -U pytest-timeout
 python3 -m pip install pyroma
 
-# TODO Remove condition when NumPy supports 3.12
-if ! [ "$GHA_PYTHON_VERSION" == "3.12-dev" ]; then python3 -m pip install numpy ; fi
+python3 -m pip install numpy
 
 # extra test images
 pushd depends && ./install_extra_test_images.sh && popd
diff --git a/.github/workflows/test-cygwin.yml b/.github/workflows/test-cygwin.yml
index 949da636069..5071e5bd442 100644
--- a/.github/workflows/test-cygwin.yml
+++ b/.github/workflows/test-cygwin.yml
@@ -102,10 +102,10 @@ jobs:
         run: |
           bash.exe .ci/install.sh
 
-      - name: Install latest NumPy
+      - name: Upgrade NumPy
         shell: dash.exe -l "{0}"
         run: |
-          python3 -m pip install -U numpy
+          python3 -m pip install -U "numpy<1.26"
 
       - name: Build
         shell: bash.exe -eo pipefail -o igncr "{0}"
diff --git a/CHANGES.rst b/CHANGES.rst
index 9cdd4cf2524..d1dce8e0d90 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,9 @@ Changelog (Pillow)
 10.1.0 (unreleased)
 -------------------
 
+- Fixed bug when reading BC5S DDS images #7401
+  [radarhere]
+
 - Prevent TIFF orientation from being applied more than once #7383
   [radarhere]
 
diff --git a/Tests/images/bc5s.png b/Tests/images/bc5s.png
index 39d7811bf2e..657d723053a 100644
Binary files a/Tests/images/bc5s.png and b/Tests/images/bc5s.png differ
diff --git a/docs/reference/Image.rst b/docs/reference/Image.rst
index 41d3b8fcec0..66e6b2a0c97 100644
--- a/docs/reference/Image.rst
+++ b/docs/reference/Image.rst
@@ -93,10 +93,14 @@ Generating images
 Registering plugins
 ^^^^^^^^^^^^^^^^^^^
 
+.. autofunction:: preinit
+.. autofunction:: init
+
 .. note::
 
-    These functions are for use by plugin authors. Application authors can
-    ignore them.
+    These functions are for use by plugin authors. They are called when a
+    plugin is loaded as part of :py:meth:`~preinit()` or :py:meth:`~init()`.
+    Application authors can ignore them.
 
 .. autofunction:: register_open
 .. autofunction:: register_mime
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 9bf293d13e8..2a6b4646bbd 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -298,7 +298,11 @@ def getmodebands(mode):
 
 
 def preinit():
-    """Explicitly load standard file format drivers."""
+    """
+    Explicitly loads BMP, GIF, JPEG, PPM and PPM file format drivers.
+
+    It is called when opening or saving images.
+    """
 
     global _initialized
     if _initialized >= 1:
@@ -334,11 +338,6 @@ def preinit():
         assert PngImagePlugin
     except ImportError:
         pass
-    # try:
-    #     import TiffImagePlugin
-    #     assert TiffImagePlugin
-    # except ImportError:
-    #     pass
 
     _initialized = 1
 
@@ -347,6 +346,9 @@ def init():
     """
     Explicitly initializes the Python Imaging Library. This function
     loads all available file format drivers.
+
+    It is called when opening or saving images if :py:meth:`~preinit()` is
+    insufficient, and by :py:meth:`~PIL.features.pilinfo`.
     """
 
     global _initialized
@@ -3407,8 +3409,12 @@ def register_open(id, factory, accept=None):
 
 def register_mime(id, mimetype):
     """
-    Registers an image MIME type.  This function should not be used
-    in application code.
+    Registers an image MIME type by populating ``Image.MIME``. This function
+    should not be used in application code.
+
+    ``Image.MIME`` provides a mapping from image format identifiers to mime
+    formats, but :py:meth:`~PIL.ImageFile.ImageFile.get_format_mimetype` can
+    provide a different result for specific images.
 
     :param id: An image format identifier.
     :param mimetype: The image MIME type for this format.
diff --git a/src/libImaging/BcnDecode.c b/src/libImaging/BcnDecode.c
index a57b74b61ac..dfd4b3e07a4 100644
--- a/src/libImaging/BcnDecode.c
+++ b/src/libImaging/BcnDecode.c
@@ -118,8 +118,8 @@ decode_bc3_alpha(char *dst, const UINT8 *src, int stride, int o, int sign) {
     if (sign == 1) {
         bc5s_alpha b;
         memcpy(&b, src, sizeof(bc5s_alpha));
-        a0 = (b.a0 + 255) / 2;
-        a1 = (b.a1 + 255) / 2;
+        a0 = b.a0 + 128;
+        a1 = b.a1 + 128;
         lut1 = b.lut[0] | (b.lut[1] << 8) | (b.lut[2] << 16);
         lut2 = b.lut[3] | (b.lut[4] << 8) | (b.lut[5] << 16);
     } else {