var that = this var ctx = wx.createCanvasContext('canvasNew', that); wx.getImageInfo({   src: 'https://xxxxxxxxxxxxxxxxxxxxxx.png',   success: function (res) { ctx.drawImage(res.path,0,0,res.width, res.height); ctx.draw(false, ()=>{   wx.canvasGetImageData({     canvasId: 'canvasNew',     x: 0,     y: 0,     width: res.width,     height: res.height,     success(result) {       let data = result.data;       for (let i = 0; i < result.width * result.height;i++){         let R = data[i * 4 + 0];         let G = data[i * 4 + 1];         let B = data[i * 4 + 2]; var avg = (R * 0.3 + G * 0.59 + B * 0.11) if (avg < 128) { data[i * 4 + 0] = 2 * avg; data[i * 4 + 1] = 0; data[i * 4 + 2] = 0; } else { data[i * 4 + 0] = 255; data[i * 4 + 1] = 2 * avg - 255; data[i * 4 + 2] = 2 * avg - 255; }       }       wx.canvasPutImageData({         canvasId: 'canvasNew',         x: 0,         y: 0,         width: res.width,         data: data,         success(res) {            console.log(res)         }, fail(e) { }       }, that)     }, fail(e){ console.log(e) }   }, that) })   } })