In a Windows 10 powershell window I entered your first line of code:

git submodule update --init --recursive
fatal: not a git repository (or any of the parent directories): .git

I have no idea what the next line means:
And then build with mingw-w64 (make).

Your instructions are referenced here https://squidfunk.github.io/mkdocs-material/setup/dependencies/image-processing/#windows_1 - I did the previous steps without issue.

I have many warnings about "visibility attribute":

pngquant/lib/blur.c: In function 'liq_max3':
pngquant/lib/blur.c:91:1: warning: visibility attribute not supported in this configuration; ignored [-Wattributes]
}
^

Do you know what this is mean?

My environment:

e:\GitHub\pngquant-winbuild>gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/dev/mingw-w64/mingw32/bin/../libexec/gcc/i686-w64-mingw32/6.2.0/lto-wrapper.exe
Target: i686-w64-mingw32
Configured with: ../../../src/gcc-6.2.0/configure --host=i686-w64-mingw32 --build=i686-w64-mingw32 --target=i686-w64-min
gw32 --prefix=/mingw32 --with-sysroot=/c/mingw620/i686-620-win32-dwarf-rt_v5-rev0/mingw32 --enable-shared --enable-stati
c --disable-multilib --enable-languages=c,c++,fortran,lto --enable-libstdcxx-time=yes --enable-threads=win32 --enable-li
bgomp --enable-libatomic --enable-lto --enable-graphite --enable-checking=release --enable-fully-dynamic-string --enable
-version-specific-runtime-libs --enable-libstdcxx-filesystem-ts=yes --disable-sjlj-exceptions --with-dwarf2 --disable-is
l-version-check --disable-libstdcxx-pch --disable-libstdcxx-debug --enable-bootstrap --disable-rpath --disable-win32-reg
istry --disable-nls --disable-werror --disable-symvers --with-gnu-as --with-gnu-ld --with-arch=i686 --with-tune=generic
--with-libiconv --with-system-zlib --with-gmp=/c/mingw620/prerequisites/i686-w64-mingw32-static --with-mpfr=/c/mingw620/
prerequisites/i686-w64-mingw32-static --with-mpc=/c/mingw620/prerequisites/i686-w64-mingw32-static --with-isl=/c/mingw62
0/prerequisites/i686-w64-mingw32-static --with-pkgversion='i686-win32-dwarf-rev0, Built by MinGW-W64 project' --with-bug
url=http://sourceforge.net/projects/mingw-w64 CFLAGS='-O2 -pipe -I/c/mingw620/i686-620-win32-dwarf-rt_v5-rev0/mingw32/op
t/include -I/c/mingw620/prerequisites/i686-zlib-static/include -I/c/mingw620/prerequisites/i686-w64-mingw32-static/inclu
de' CXXFLAGS='-O2 -pipe -I/c/mingw620/i686-620-win32-dwarf-rt_v5-rev0/mingw32/opt/include -I/c/mingw620/prerequisites/i6
86-zlib-static/include -I/c/mingw620/prerequisites/i686-w64-mingw32-static/include' CPPFLAGS= LDFLAGS='-pipe -L/c/mingw6
20/i686-620-win32-dwarf-rt_v5-rev0/mingw32/opt/lib -L/c/mingw620/prerequisites/i686-zlib-static/lib -L/c/mingw620/prereq
uisites/i686-w64-mingw32-static/lib -Wl,--large-address-aware'
Thread model: win32
gcc version 6.2.0 (i686-win32-dwarf-rev0, Built by MinGW-W64 project)

Since we build one set of object files with IMAGEQUANT_EXPORTS defined, the pngquant executable also exports the functions like the dll.

Fixing this would require building separate object files for the executable and dll.

Thanks a lot for providing this!

I definitely do not want it to turn into a programming lesson! Just wanted to say that neither binary works for me on latest Win10x64. Both, when asked why, say:

Untitled-1.png:
  read 151KB file
Skipped 1 file out of a total of 1 file.

And make says:

\pngquant-winbuild>make
gcc -Wall -O2 -msse -fopenmp -flto -fvisibility=hidden -DNDEBUG -D_LARGEFILE64_SOURCE=1 -DUSE_SSE=1 -DUSE_LCMS=1 -DIMAGEQUANT_EXPORTS -I zlib -I libpng -I lcms2/include -fno-math-errno -funroll-loops -fomit-frame-pointer -fexcess-precision=fast -c -o pngquant/pngquant.o pngquant/pngquant.c
pngquant/pngquant.c:84:17: fatal error: omp.h: No such file or directory
 #include <omp.h>
                 ^
compilation terminated.
make: *** [Makefile:56: pngquant/pngquant.o] Error 1

Thanks anyway, I will figure out a way!

Building with MSVC currently fails:

• There is an issue with delcaring variables in OpenMP for loops (kornelski/pngquant#211)
• pngquant.c uses getopt, which is not available with MSVC

Why imagequant.dll (at least 32-bit version) require MessageBoxW function from user32.dll?