<image.loadPNG> libpng package not found, please install libpng

[TingtingLiao]

/home/ting/torch/install/share/lua/5.1/dok/inline.lua:738: <image.loadPNG> libpng package not found, please install libpng
stack traceback:
[C]: in function 'error'
/home/ting/torch/install/share/lua/5.1/dok/inline.lua:738: in function 'error'
/home/ting/torch/install/share/lua/5.1/image/init.lua:153: in function 'loader'
/home/ting/torch/install/share/lua/5.1/image/init.lua:388: in function 'load'
/home/ting/torch/install/share/lua/5.1/image/test.lua:538: in function 'checkPNG'
/home/ting/torch/install/share/lua/5.1/image/test.lua:675: in function </home/ting/torch/install/share/lua/5.1/image/test.lua:664>
[C]: in function 'xpcall'
/home/ting/torch/install/share/lua/5.1/torch/Tester.lua:477: in function '_pcall'
/home/ting/torch/install/share/lua/5.1/torch/Tester.lua:436: in function '_run'
/home/ting/torch/install/share/lua/5.1/torch/Tester.lua:355: in function 'run'
/home/ting/torch/install/share/lua/5.1/image/test.lua:708: in function 'test'
(command line):1: in main chunk
[C]: at 0x55d3d10fc0e0

[TingtingLiao]

I have solved this by:
· sudo apt-get install libpng-dev
· sudo apt-get install libsdl2-dev