How to fix python `dlib` error: "symbol not found in flat namespace '_png_do_expand_palette_rgb8_neon'"?

Question

I am getting the error: symbol not found in flat namespace '_png_do_expand_palette_rgb8_neon' The error occurs in spite of the dlib package being installed for the relevant Python version.

I am using VSCode, in case that is relevant.

Can anyone please help me to fix this bug?

Answer 1

For me, this is a mac M1 specific issue, solved by linking libpng:

brew install libpng
export C_INCLUDE_PATH=/opt/homebrew/Cellar/libpng/1.6.37/include
export LIBRARY_PATH=/opt/homebrew/Cellar/libpng/1.6.37/lib
pip3 install dlib --force-reinstall 

(replace 1.6.37 by your installed version of libpng)

Answer 2

I ended up having to install dlib from source:

git clone https://github.com/davisking/dlib.git
cd dlib
python setup.py install --set DLIB_PNG_SUPPORT=1 --compiler-flags "-I/usr/local/include -L/opt/homebrew/lib -lpng"

This was based on this issue on dlib which recommends installing libpng and this issue on homebrew which recommends adding the --compiler-flags .

Installing libpng and setting the compiler flags didn't make the error go away, and in desperation I went into dlib/image_save/save_png.h to comment out the assert. However, there was a helpful commend in the code:

#ifndef DLIB_PNG_SUPPORT
            /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                You are getting this error because you are trying to use save_png()
                but you haven't defined DLIB_PNG_SUPPORT.  You must do so to use
                this function.   You must also make sure you set your build environment
                to link against the libpng library.
            !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
            COMPILE_TIME_ASSERT(sizeof(image_type) == 0);
#else
...

Given that I have libpng, I set DLIB_PNG_SUPPORT and building succeeded.

Then ensure your virtual environment is active (if applicable) and install it:

python -m pip install .

Answer 3

Should work if you force a reinstall using:

pip3 install dlib --force-reinstall --no-cache-dir --global-option=build_ext

That fixed it for me.