编译错误：
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgb8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_init_filter_functions_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgba8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_riffle_palette_neon'
collect2: 错误： ld 返回 1
make2: *** apps/model-diagnostics/CMakeFiles/opencv_model_diagnostics.dir/build.make:98：bin/opencv_model_diagnostics 错误 1
make1: *** CMakeFiles/Makefile2:1506：apps/model-diagnostics/CMakeFiles/opencv_model_diagnostics.dir/all 错误 2
make1: *** 正在等待未完成的任务....
100% Building CXX object apps/interactive-calibration/CMakeFiles/opencv_interactive-calibration.dir/rotationConverters.cpp.o
100% Linking CXX executable ../../bin/opencv_version
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgb8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_init_filter_functions_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgba8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_riffle_palette_neon'
collect2: 错误： ld 返回 1
make2: *** apps/version/CMakeFiles/opencv_version.dir/build.make:98：bin/opencv_version 错误 1
make1: *** CMakeFiles/Makefile2:1480：apps/version/CMakeFiles/opencv_version.dir/all 错误 2
100% Linking CXX executable ../../bin/opencv_annotation
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgb8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_init_filter_functions_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgba8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_riffle_palette_neon'
collect2: 错误： ld 返回 1
make2: *** apps/annotation/CMakeFiles/opencv_annotation.dir/build.make:98：bin/opencv_annotation 错误 1
make1: *** CMakeFiles/Makefile2:1402：apps/annotation/CMakeFiles/opencv_annotation.dir/all 错误 2
100% Linking CXX executable ../../bin/opencv_visualisation
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgb8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_init_filter_functions_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgba8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_riffle_palette_neon'
collect2: 错误： ld 返回 1
make2: *** apps/visualisation/CMakeFiles/opencv_visualisation.dir/build.make:98：bin/opencv_visualisation 错误 1
make1: *** CMakeFiles/Makefile2:1428：apps/visualisation/CMakeFiles/opencv_visualisation.dir/all 错误 2
100% Linking CXX executable ../../bin/opencv_interactive-calibration
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgb8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_init_filter_functions_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_do_expand_palette_rgba8_neon'
/home/lm/software/all_toolchains/rk-linux/gcc-arm-8.3-2019.03-x86_64-arm-linux-gnueabihf/bin/../lib/gcc/arm-linux-gnueabihf/8.3.0/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_world.so.4.5.4: undefined reference to `png_riffle_palette_neon'
collect2: 错误： ld 返回 1
make2: *** apps/interactive-calibration/CMakeFiles/opencv_interactive-calibration.dir/build.make:178：bin/opencv_interactive-calibration 错误 1
make1: *** CMakeFiles/Makefile2:1454：apps/interactive-calibration/CMakeFiles/opencv_interactive-calibration.dir/all 错误 2
make: *** Makefile:166：all 错误 2
libopencv_world.so.4.5.4 依赖了以下几个符号：
png_do_expand_palette_rgb8_neonpng_init_filter_functions_neonpng_do_expand_palette_rgba8_neonpng_riffle_palette_neon
解决：
打开opencv源码目录，编辑文件 vim 3rdparty/libpng/pngpriv.h
第130行注释掉， 修改为131行
