在node.js中调整图像大小

Question

我试图通过这个程序调整node.js中的图像大小.

https://github.com/LearnBoost/node-canvas/blob/master/examples/resize.js

var Canvas = require('canvas')
  , Image = Canvas.Image
  , fs = require('fs');

var img = new Image
  , start = new Date;
img.src = __dirname + 'flowers.jpg';

console.log('Resized and saved in %dms');
img.onload = function(){
  console.log('Resized and saved in buffer');
  try{
  var width = img.width / 2
    , height = img.height / 2
    , canvas = new Canvas(width, height)
    , ctx = canvas.getContext('2d');
  ctx.drawImage(img, 0, 0, width, height);
  canvas.toBuffer(function(err, buf){
    console.log('Resized and saved in buffer');
    fs.writeFile(__dirname + '/resize.jpg', buf, function(){
      console.log('Resized and saved in %dms', new Date - start);
    });
  });
  }catch(e){
    console.log(sys.inspect(e));
  }
};

img.onerror = function(err){
  throw err;
};

程序是不是在onload函数中为什么？编辑:在附加onload和onerror事件后尝试img.src时出现此错误？

`Resized and saved in NaNms

/home/reach121/rahul/knox/index.js:33
 throw err;
 ^
Error: error while reading from input stream
   at Object.<anonymous> (/home/reach121/rahul/knox/index.js:35:9)
   at Module._compile (module.js:404:26)
   at Object..js (module.js:410:10)
   at Module.load (module.js:336:31)
   at Function._load (module.js:297:12)
   at Array.0 (module.js:423:10)
   at EventEmitter._tickCallback (node.js:170:26)

使用Image Magic给我这个错误:

reach121@youngib:~/rahul/knox$ sudo node index.js

node.js:178
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: Command failed: execvp(): No such file or directory

    at ChildProcess.<anonymous> (/usr/local/lib/node/.npm/imagemagick/0.1.2/package/imagemagick.js:64:15)
    at ChildProcess.emit (events.js:67:17)
    at Socket.<anonymous> (child_process.js:172:12)
    at Socket.emit (events.js:64:17)
    at Array.<anonymous> (net.js:826:12)
    at EventEmitter._tickCallback (node.js:170:26)

代码:

var im = require('imagemagick');

im.resize({
  srcPath: __dirname + '/flowers.jpg',
  dstPath: __dirname + '/flowers-small.jpg',
  width:   '50%'
}, function(err, stdout, stderr){
  if (err) throw err
  console.log('resized')
});

Answer 1

您是否img.src在附加onload和onerror事件后尝试过设置？刚刚注意到这是原始示例与您的示例之间的差异.

另一个问题:onerror事件是否被触发？如果是这样,抛出的异常可能会有所帮助.

更新

如果您只想调整图像大小而不需要使用任何特定于画布的操作,只需使用ImageMagick和node-imagemagick即可.我只做了一个小测试,开箱即用:

var im = require('imagemagick');

im.resize({
  srcPath: __dirname + '/koala.jpg',
  dstPath: __dirname + '/koala-small.jpg',
  width:   '50%'
}, function(err, stdout, stderr){
  if (err) throw err
  console.log('resized')
});