前端js实现Blob、DataURL、canvas、image的相互转换

canvas转dataURL：canvas对象、转换格式、图像品质

function canvasToDataURL(canvas, format, quality){
	return canvas.toDataURL(format||'image/jpeg', quality||1.0);
}

DataURL转canvas

function dataURLToCanvas(dataurl, cb){
	var canvas = document.createElement('CANVAS');
	var ctx = canvas.getContext('2d');
	var img = new Image();
	img.onload = function(){
		canvas.width = img.width;
		canvas.height = img.height;
		ctx.drawImage(img, 0, 0);
		cb(canvas);
	};
	img.src = dataurl;
}

image转canvas：图片地址

function imageToCanvas(src, cb){
	var canvas = document.createElement('CANVAS');
	var ctx = canvas.getContext('2d');
	var img = new Image();
	img.src = src;
	img.onload = function (){
		canvas.width = img.width;
		canvas.height = img.height;
		ctx.drawImage(img, 0, 0);
		cb(canvas);
	};
}

canvas转image

function canvasToImage(canvas){
	var img = new Image();
	img.src = canvas.toDataURL('image/jpeg', 1.0);
	return img;
}

File/Blob对象转DataURL

function fileOrBlobToDataURL(obj, cb){
	var a = new FileReader();
	a.readAsDataURL(obj);
	a.onload = function (e){
		cb(e.target.result);
	};
}

DataURL转Blob对象

function dataURLToBlob(dataurl){
	var arr = dataurl.split(',');
	var mime = arr[0].match(/:(.*?);/)[1];
	var bstr = atob(arr[1]);
	var n = bstr.length;
	var u8arr = new Uint8Array(n);
	while(n--){
		u8arr[n] = bstr.charCodeAt(n);
	}
	return new Blob([u8arr], {type:mime});
}

Blob转image

function blobToImage(blob, cb){
	fileOrBlobToDataURL(blob, function (dataurl){
		var img = new Image();
		img.src = dataurl;
		cb(img);
	});
}

image转Blob

function imageToBlob(src, cb){
	imageToCanvas(src, function (canvas){
		cb(dataURLToBlob(canvasToDataURL(canvas)));
	});
}

Blob转canvas

function BlobToCanvas(blob, cb){
	fileOrBlobToDataURL(blob, function (dataurl){
		dataURLToCanvas(dataurl, cb);
	});
}

canvas转Blob

function canvasToBlob(canvas, cb){
	cb(dataURLToBlob(canvasToDataURL(canvas)));
}

image转dataURL

function imageToDataURL(src, cb){
	imageToCanvas(src, function (canvas){
		cb(canvasToDataURL(canvas));
	});
}

dataURL转image，这个不需要转，直接给了src就能用

function dataURLToImage(dataurl){
	var img = new Image();
	img.src = d;
	return img;
}

摘自

http://www.fly63.com/article/detial/2859