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背景：

在了解 Tesseract 的识别效果的时候，有个demo项目很好用。有个小毛病，就是没事都要从摄像头抓取图片，然后进行识别。如果可以从本地读取图，就更方便了。

实现：

1. 下载项目代码：https://github.com/kdzwinel/JS-OCR-demo

2. 在页面index.html增加选择文件的input组件

   51|<input type="file" id="uploadImage" accept="image/*" class="btn btn-lg btn-default" style="justify-self: center;margin-top: 10px;">
   

3. 在main.js修改方法：

• 增加加载本地图片的逻辑。

     // 新增：本地图片上传$('#uploadImage').on('change', function (e) {var file = e.target.files[0];if (!file) return;var reader = new FileReader();reader.onload = function (evt) {var img = document.querySelector('#step2 img');img.onload = function () {// 将图片绘制到canvasvar canvas = document.querySelector('#step2 canvas');canvas.width = pictureWidth;canvas.height = pictureHeight;var ctx = canvas.getContext('2d');ctx.drawImage(img, 0, 0, canvas.width, canvas.height);texture = fxCanvas.texture(canvas);fxCanvas.draw(texture).hueSaturation(-1, -1)//grayscale.unsharpMask(20, 2).brightnessContrast(0.2, 0.9).update();$('.jcrop-holder img').attr('src', fxCanvas.toDataURL());$(img).attr('src', fxCanvas.toDataURL());};img.src = evt.target.result;};reader.readAsDataURL(file);step2(false);changeStep(2);});
  

• 修改step2方法：增加参数判断，区分使用的相机截图，还是本地文件；截图时，使用图片真实像素为基准。

  function step2(usevideo=true) {var canvas = document.querySelector('#step2 canvas');var img = document.querySelector('#step2 img');//setup canvascanvas.width = pictureWidth;canvas.height = pictureHeight;var ctx = canvas.getContext('2d');if(usevideo){//draw picture from video on canvasctx.drawImage(video, 0, 0);console.log('draw picture from video on canvas');}//modify the picture using glfx.js filterstexture = fxCanvas.texture(canvas);fxCanvas.draw(texture).hueSaturation(-1, -1)//grayscale.unsharpMask(20, 2).brightnessContrast(0.2, 0.9).update();window.texture = texture;window.fxCanvas = fxCanvas;$(img)//setup the crop utility.one('load', function () {if (!$(img).data().Jcrop) {$(img).Jcrop({onSelect: function () {//Enable the 'done' button$('#adjust').removeAttr('disabled');},trueSize: [img.naturalWidth || img.width, img.naturalHeight || img.height]});} else {//update crop tool (it creates copies of <img> that we have to update manually)$('.jcrop-holder img').attr('src', fxCanvas.toDataURL());}})//show output from glfx.js.attr('src', fxCanvas.toDataURL());
  }
  

• 修改step3方法：截图区域不再使用缩放系数计算；修改识别语言为中文chi_sim

  function step3() {var canvas = document.querySelector('#step3 canvas');var step2Image = document.querySelector('#step2 img');var cropData = $(step2Image).data().Jcrop.tellSelect();// 直接使用裁剪区域的宽高canvas.width = cropData.w;canvas.height = cropData.h;var ctx = canvas.getContext('2d');ctx.drawImage(step2Image,cropData.x, cropData.y, cropData.w, cropData.h, // 源区域0, 0, cropData.w, cropData.h                    // 目标区域);var spinner = $('.spinner');spinner.show();$('blockquote p').text('');$('blockquote footer').text('');// do the OCR!// 设置参数var options = 'chi_sim+eng';Tesseract.recognize(ctx, options).then(function (result) {var resultText = result.text ? result.text.trim() : '';//show the resultspinner.hide();$('blockquote p').html('„' + resultText + '“');$('blockquote footer').text('(' + resultText.length + ' characters)');});}