ios上传图片转base64后 图片镜像问题怎么解决

wx.canvasGetImageData({

canvasId: "shopCanvas",

x: 0,

y: 0,

width: width,

height: height,

success(res) {

console.log("canvas:图片",res.data);

let pngData = upng.encode([res.data.buffer], res.width, res.height)

let base64 = wx.arrayBufferToBase64(pngData);

imgBase64 = 'data:image/png;base64,' + base64;

}

})