node-png libpng dependency

You should probably state that *libpng* has to be installed for node-png which you depend on.

	Package libpng was not found in the pkg-config search path.
	Perhaps you should add the directory containing `libpng.pc'
	to the PKG_CONFIG_PATH environment variable
	No package 'libpng' found
	gyp: Call to 'pkg-config libpng --libs' returned exit status 1. while trying to load binding.gyp
	gyp ERR! configure error
	gyp ERR! stack Error: `gyp` failed with exit code: 1
	gyp ERR! stack     at ChildProcess.onCpExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:343:16)
	gyp ERR! stack     at ChildProcess.emit (events.js:98:17)
	gyp ERR! stack     at Process.ChildProcess._handle.onexit (child_process.js:809:12)
	gyp ERR! System Darwin 13.3.0
	 command "node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
	gyp ERR! cwd /Users/thomas/dev/psd.js/node_modules/png
	gyp ERR! node -v v0.10.29
	gyp ERR! node-gyp -v v0.13.1
	gyp ERR! not ok
	npm ERR! png@3.0.3 install: `node-gyp rebuild`
	npm ERR! Exit status 1
	npm ERR!
	npm ERR! Failed at the png@3.0.3 install script.
	npm ERR! This is most likely a problem with the png package,
	npm ERR! not with npm itself.
	npm ERR! Tell the author that this fails on your system:
	npm ERR!     node-gyp rebuild
	npm ERR! You can get their info via:
	npm ERR!     npm owner ls png
	npm ERR! There is likely additional logging output above.

	npm ERR! System Darwin 13.3.0
	npm ERR! command "node" "/usr/local/bin/npm" "install"
	npm ERR! cwd /Users/thomas/dev/psd.js
	npm ERR! node -v v0.10.29
	npm ERR! npm -v 1.5.0-alpha-1
	npm ERR! code ELIFECYCLE
	npm ERR!
	npm ERR! Additional logging details can be found in:
	npm ERR!     /Users/thomas/dev/psd.js/npm-debug.log
	npm ERR! not ok code 0

When I install libpng via homebrew it still throws:

    -
    > png@3.0.3 install /Users/thomas/dev/photoshop/node_modules/png
    > node-gyp rebuild

      CXX(target) Release/obj.target/png/src/common.o
      CXX(target) Release/obj.target/png/src/png_encoder.o
    In file included from ../src/png_encoder.cpp:3:
    ../src/png_encoder.h:4:10: error: 'png.h' file not found with <angled> include;
          use "quotes" instead
    #include <png.h>
             ^~~~~~~
             "png.h"
    ../src/png_encoder.h:19:36: error: unknown type name 'png_structp'
        static void png_chunk_producer(png_structp png_ptr, png_bytep data, ...
                                       ^
    ../src/png_encoder.h:19:57: error: unknown type name 'png_bytep'
        static void png_chunk_producer(png_structp png_ptr, png_bytep data, ...
                                                            ^
    ../src/png_encoder.h:19:73: error: unknown type name 'png_size_t'; did you mean
          'vm_size_t'?
      ...png_chunk_producer(png_structp png_ptr, png_bytep data, png_size_t length);
                                                                 ^~~~~~~~~~
                                                                 vm_size_t
    /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/mach/i386/vm_types.h:112:20: note:
          'vm_size_t' declared here
    typedef uintptr_t               vm_size_t;
                                    ^
    ../src/png_encoder.cpp:7:32: error: unknown type name 'png_structp'
    PngEncoder::png_chunk_producer(png_structp png_ptr, png_bytep data, png_...
                                   ^
    ../src/png_encoder.cpp:7:53: error: unknown type name 'png_bytep'
    PngEncoder::png_chunk_producer(png_structp png_ptr, png_bytep data, png_...
                                                        ^
    ../src/png_encoder.cpp:7:69: error: unknown type name 'png_size_t'; did you mean
          'vm_size_t'?
      ...png_ptr, png_bytep data, png_size_t length)
                                  ^~~~~~~~~~
                                  vm_size_t
    /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/mach/i386/vm_types.h:112:20: note:
          'vm_size_t' declared here
    typedef uintptr_t               vm_size_t;
                                    ^
    ../src/png_encoder.cpp:48:5: error: unknown type name 'png_structp'
        png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING...
        ^
    ../src/png_encoder.cpp:48:51: error: use of undeclared identifier
          'PNG_LIBPNG_VER_STRING'
        png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING...
                                                      ^
    ../src/png_encoder.cpp:52:5: error: unknown type name 'png_infop'
        png_infop info_ptr = png_create_info_struct(png_ptr);
        ^
    ../src/png_encoder.cpp:60:22: error: use of undeclared identifier
          'PNG_COLOR_TYPE_RGB'
            color_type = PNG_COLOR_TYPE_RGB;
                         ^
    ../src/png_encoder.cpp:63:22: error: use of undeclared identifier
          'PNG_COLOR_TYPE_GRAY'
            color_type = PNG_COLOR_TYPE_GRAY;
                         ^
    ../src/png_encoder.cpp:66:22: error: use of undeclared identifier
          'PNG_COLOR_TYPE_RGB_ALPHA'
            color_type = PNG_COLOR_TYPE_RGB_ALPHA;
                         ^
    ../src/png_encoder.cpp:73:5: error: unknown type name 'png_bytep'
        png_bytep *row_pointers = NULL;
        ^
    ../src/png_encoder.cpp:83:9: error: unknown type name 'png_bytep'
            png_bytep *row_pointers = (png_bytep *)malloc(sizeof(png_bytep) ...
            ^
    ../src/png_encoder.cpp:83:36: error: use of undeclared identifier 'png_bytep'
            png_bytep *row_pointers = (png_bytep *)malloc(sizeof(png_bytep) ...
                                       ^
    ../src/png_encoder.cpp:83:47: error: expected expression
            png_bytep *row_pointers = (png_bytep *)malloc(sizeof(png_bytep) ...
                                                  ^
    17 errors generated.
    make: *** [Release/obj.target/png/src/png_encoder.o] Error 1
    gyp ERR! build error
    gyp ERR! stack Error: `make` failed with exit code: 2
    gyp ERR! stack     at ChildProcess.onExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/build.js:267:23)
    gyp ERR! stack     at ChildProcess.emit (events.js:98:17)
    gyp ERR! stack     at Process.ChildProcess._handle.onexit (child_process.js:809:12)
    gyp ERR! System Darwin 13.3.0
    gyp ERR! command "node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
    gyp ERR! cwd /Users/thomas/dev/photoshop/node_modules/png
    gyp ERR! node -v v0.10.29
    gyp ERR! node-gyp -v v0.13.1
    gyp ERR! not ok
    npm ERR! png@3.0.3 install: `node-gyp rebuild`
    npm ERR! Exit status 1
    npm ERR!
    npm ERR! Failed at the png@3.0.3 install script.
    npm ERR! This is most likely a problem with the png package,
    npm ERR! not with npm itself.
    npm ERR! Tell the author that this fails on your system:
    npm ERR!     node-gyp rebuild
    npm ERR! You can get their info via:
    npm ERR!     npm owner ls png
    npm ERR! There is likely additional logging output above.

    npm ERR! System Darwin 13.3.0
    npm ERR! command "node" "/usr/local/bin/npm" "install" "png"
    npm ERR! cwd /Users/thomas/dev/photoshop
    npm ERR! node -v v0.10.29
    npm ERR! npm -v 1.5.0-alpha-1
    npm ERR! code ELIFECYCLE
    npm ERR!
    npm ERR! Additional logging details can be found in:
    npm ERR!     /Users/thomas/dev/photoshop/npm-debug.log
    npm ERR! not ok code 0

I totally know that you aren't responsible for node-png. Looking at the node-png issues page it seems like a lot of people have troubles compiling. Maybe there is a more suitable lib for generating the pngs? Just braindripping here, I'm trying to use psd.js as a lib for a little tool but I can't force people to manually resolve problems with node-png upon installation.