uniapp h5页面图片压缩 blob图片放大后页面展示空白问题

	uni.chooseImage({
		count: 1, //默认9
		sourceType: ['camera'], //拍照
		success: (res) => {
			// 设置url的值，显示控件
			getImage(res.tempFilePaths[0])
		}
	});


const getImage = (src) => {
	console.log(src);
	uni.getImageInfo({  // 获取图片信息
		src,
		success(res) {
			let canvasWidth = res.width; 
			let canvasHeight = res.height;
			let img = new Image();
			img.src = res.path;
			let canvas = document.createElement('canvas');
			let ctx = canvas.getContext('2d');
			canvas.width = canvasWidth / 2;
			canvas.height = canvasHeight / 2;
			ctx.drawImage(img, 0, 0, canvasWidth / 2, canvasHeight / 2);
			canvas.toBlob((file) => {
				let imgSrc = window.URL.createObjectURL(file);
				url.value = imgSrc;  // 赋值
			});
		}
	});
};