function dealImage(base64, w, callback) {
var newImage = new Image();
var quality = 0.5;
newImage.src = base64;
newImage.setAttribute("crossOrigin", 'Anonymous');
var imgWidth, imgHeight;
newImage.onload = function () {
imgWidth = this.width;
imgHeight = this.height;
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
if (Math.max(imgWidth, imgHeight) > w) {
if (imgWidth > imgHeight) {
canvas.width = w;
canvas.height = w * imgHeight / imgWidth;
} else {
canvas.height = w;
canvas.width = w * imgWidth / imgHeight;
}
} else {
canvas.width = imgWidth;
canvas.height = imgHeight;
quality = 0.6;
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.drawImage(this, 0, 0, canvas.width, canvas.height);
var base64 = canvas.toDataURL("image/jpeg", quality);
while (base64.length / 1024 > 50) {
quality -= 0.01;
base64 = canvas.toDataURL("image/jpeg", quality);
}
while (base64.length / 1024 < 30) {
quality += 0.001;
base64 = canvas.toDataURL("image/jpeg", quality);
}
callback(base64);
}
}