错误
usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: ../../lib/libopencv_imgcodecs.so.4.2.0: undefined reference to `png_riffle_palette_neon' collect2: error: ld returned 1 exit status make[2]: *** [apps/annotation/CMakeFiles/opencv_annotation.dir/build.make:89：bin/opencv_annotation] 错误 1 make[1]: *** [CMakeFiles/Makefile2:3746：apps/annotation/CMakeFiles/opencv_annotation.dir/all]
错误 2
解决办法
方法一：无效
进入到3rdparty/libpng，在CMakeLists.txt顶端增加：
set(ENABLE_NEON ON)
方法二：有效
${HOME}/opencv-3.3.1/3rdparty/libpng/pngpriv.h
/*# if (defined(ARM_NEON) || defined(__ARM_NEON)) && */ if defined(PNG_ARM_NEON) && (defined(ARM_NEON) || defined(__ARM_NEON)) && \
如上所示，把上面的一行注释掉，增加下面一行。再次make即可。
