wxml：

<image style="width: {{imagewidth}}px; height: {{imageheight}}px;"  src="{{imagefirstsrc}}" bindload="imageLoad"></image>  

JS

//index.js  

//获取应用实例  

var imageUtil = require(\'../../utils/util.js\');  

var app = getApp()  

Page({  

　　data: {  

      imagefirstsrc: \'http://bpic.588ku.com/back_pic/00/03/85/1656205138bbe2d.png\',//图片链接  

      imagesecondsrc: \'http://bpic.588ku.com/back_pic/04/07/63/28581203949ca9d.jpg!/fw/400/quality/90/unsharp/true/compress/true\',//图片链接  

      imagethirdsrc:\'http://img1.gtimg.com/ent/pics/hv1/13/71/2061/134034643.jpg\',  

      imagewidth: 0,//缩放后的宽  

      imageheight: 0,//缩放后的高  

 　　 },  

 　  onLoad: function () {  

 　　 },  

 　  imageLoad: function (e) {  

　　var imageSize = imageUtil.imageUtil(e)  

　　this.setData({  

      imagewidth: imageSize.imageWidth,  

      imageheight: imageSize.imageHeight  

  })  

  }  

})  

Util.js

function imageUtil(e) {
var imageSize = {};
var originalWidth = e.detail.width;//图片原始宽
var originalHeight = e.detail.height;//图片原始高
var originalScale = originalHeight / originalWidth;//图片高宽比
console.log(\'originalWidth: \' + originalWidth)
console.log(\'originalHeight: \' + originalHeight)
//获取屏幕宽高
wx.getSystemInfo({
success: function (res) {
var windowWidth = res.windowWidth;
var windowHeight = res.windowHeight;
var windowscale = windowHeight / windowWidth;//屏幕高宽比
console.log(\'windowWidth: \' + windowWidth)
console.log(\'windowHeight: \' + windowHeight)
if (originalScale < windowscale) {//图片高宽比小于屏幕高宽比
//图片缩放后的宽为屏幕宽
imageSize.imageWidth = windowWidth;
imageSize.imageHeight = (windowWidth * originalHeight) / originalWidth;
} else {//图片高宽比大于屏幕高宽比
//图片缩放后的高为屏幕高
imageSize.imageHeight = windowHeight;
imageSize.imageWidth = (windowHeight * originalWidth) / originalHeight;
}

}
})
console.log(\'缩放后的宽: \' + imageSize.imageWidth)
console.log(\'缩放后的高: \' + imageSize.imageHeight)
return imageSize;
}

module.exports = {
imageUtil: imageUtil
}