ChatGPT解决这个技术问题 Extra ChatGPT

How To Save Canvas As An Image With canvas.toDataURL()?

I'm currently building a HTML5 web app/Phonegap native app and I can't seem to figure out how to save my canvas as an image with canvas.toDataURL(). Can somebody help me out?

Here's the code, what's wrong with it?

//My canvas was named "canvasSignature"

JavaScript:

function putImage()
{
  var canvas1 = document.getElementById("canvasSignature");        
  if (canvas1.getContext) {
     var ctx = canvas1.getContext("2d");                
     var myImage = canvas1.toDataURL("image/png");      
  }
  var imageElement = document.getElementById("MyPix");  
  imageElement.src = myImage;                           

}  

HTML5:

<div id="createPNGButton">
    <button onclick="putImage()">Save as Image</button>        
</div>
OP's question has not been answered. He clearly said this is for Phonegap / iPad. The answers given are for saving on a desktop browser.
Not sure about phonegap, but I've done this from scratch in native iOS using JavaScript on the other end, I capture the data with .toDataURL(), then use window.location to point the browser to appname://[data url]. On the app end, the UIWebView has a delegate method that says whether or not it should load a page. I listen for appname:// and break it down when it comes in, deny the page load and capture the data url in a native string... how familiar are you with actual iOS/Objective C code?

H
Hauleth

Here is some code. without any error.

var image = canvas.toDataURL("image/png").replace("image/png", "image/octet-stream");  // here is the most important part because if you dont replace you will get a DOM 18 exception.


window.location.href=image; // it will save locally

Except in IE9 standards mode: "Some content or files on this webpage require a program that you don't have installed." Internet Explorer 8 and above only supports data URIs for images in CSS, <link>, and <img>: developer.mozilla.org/en-US/docs/data_URIs
works fine. how can I change the name of downloaded file? it's coming just "download" and without extension. thanks!
In Chrome this crashes the browser. If I display the image in an image tag, it does work but the right-click menu is greyed out - so I still can't save the image.
This works great... But in Android (Default browser in Galaxy S3) it just doesn't download the image, but i get the message "Downloading..." forever.
I have save issue some one can help me see this link :stackoverflow.com/questions/25131763/…
T
Thomas Wagenaar

This solution allows you to change the name of the downloaded file:

HTML:

<a id="link"></a>

JAVASCRIPT:

  var link = document.getElementById('link');
  link.setAttribute('download', 'MintyPaper.png');
  link.setAttribute('href', canvas.toDataURL("image/png").replace("image/png", "image/octet-stream"));
  link.click();

Thank you for this, it has helped me greatly!
No need to replace.
W
Woold

You can try this; create a dummy HTML anchor, and download the image from there like...

// Convert canvas to image
document.getElementById('btn-download').addEventListener("click", function(e) {
    var canvas = document.querySelector('#my-canvas');

    var dataURL = canvas.toDataURL("image/jpeg", 1.0);

    downloadImage(dataURL, 'my-canvas.jpeg');
});

// Save | Download image
function downloadImage(data, filename = 'untitled.jpeg') {
    var a = document.createElement('a');
    a.href = data;
    a.download = filename;
    document.body.appendChild(a);
    a.click();
}

I like the fact that everything was done in JS, including the creation of the link element. It works great for automation purposes
Perfect solution
No need to appendChild.
S
Suresh Atta

You can use canvas2image to prompt for download.

I had the same issue, here's a simple example that both adds the image to the page and forces the browser to download it:

<html>
    <head>
        <script src="http://hongru.github.io/proj/canvas2image/canvas2image.js"></script>
        <script>
            function draw(){
                var canvas = document.getElementById("thecanvas");
                var ctx = canvas.getContext("2d");
                ctx.fillStyle = "rgba(125, 46, 138, 0.5)";
                ctx.fillRect(25,25,100,100); 
                ctx.fillStyle = "rgba( 0, 146, 38, 0.5)";
                ctx.fillRect(58, 74, 125, 100);
            }

            function to_image(){
                var canvas = document.getElementById("thecanvas");
                document.getElementById("theimage").src = canvas.toDataURL();
                Canvas2Image.saveAsPNG(canvas);
            }
        </script>
    </head>
    <body onload="draw()">
        <canvas width=200 height=200 id="thecanvas"></canvas>
        <div><button onclick="to_image()">Draw to Image</button></div>
        <image id="theimage"></image>
    </body>
</html>

Just tried it out, it will save a file with no name nor extension in Chrome.
as mentioned here nihilogic.dk/labs/canvas2image setting the file name doesn't seem to be possible: "It would be really neat if somehow a filename could be attached to the data, but I've found no way to do that. For now, you have to specify the filename yourself."
The link you posted is broken
To download with file name and extension: stackoverflow.com/a/56185896/4906752
g
gillyb

I created a small library that does this (along with some other handy conversions). It's called reimg, and it's really simple to use.

ReImg.fromCanvas(yourCanvasElement).toPng()


Cool library. Thanks. There's a small issue in the example documentation though. I opened an issue on Github to bring it to your attention.
C
Community

Similar to 1000Bugy's answer but simpler because you don't have to make an anchor on the fly and dispatch a click event manually (plus an IE fix).

If you make your download button an anchor you can highjack it right before the default anchor functionality is run. So onAnchorClick you can set the anchor href to the canvas base64 image and the anchor download attribute to whatever you want to name your image.

This does not work in (the current) IE because it doesn't implement the download attribute and prevents download of data uris. But this can be fixed by using window.navigator.msSaveBlob instead.

So your anchor click event handler would be as followed (where anchor, canvas and fileName are scope lookups):

function onClickAnchor(e) {
  if (window.navigator.msSaveBlob) {
    window.navigator.msSaveBlob(canvas.msToBlob(), fileName);
    e.preventDefault();
  } else {
    anchor.setAttribute('download', fileName);
    anchor.setAttribute('href', canvas.toDataURL());
  }
}

Here's a fiddle


1
1000Bugy

This work for me: (Only google chrome)

<html>
<head>
    <script>
            function draw(){
                var canvas = document.getElementById("thecanvas");
                var ctx = canvas.getContext("2d");
                ctx.fillStyle = "rgba(125, 46, 138, 0.5)";
                ctx.fillRect(25,25,100,100);
                ctx.fillStyle = "rgba( 0, 146, 38, 0.5)";
                ctx.fillRect(58, 74, 125, 100);
            }

            function downloadImage()
            {
                var canvas = document.getElementById("thecanvas");
                var image = canvas.toDataURL();

                var aLink = document.createElement('a');
                var evt = document.createEvent("HTMLEvents");
                evt.initEvent("click");
                aLink.download = 'image.png';
                aLink.href = image;
                aLink.dispatchEvent(evt);
            }
    </script>
</head>
<body onload="draw()">
    <canvas width=200 height=200 id="thecanvas"></canvas>
    <div><button onclick="downloadImage()">Download</button></div>
    <image id="theimage"></image>
</body>
</html>

Perhaps you could explain the part of your code which answers the question instead of just pasting it without any comments?
H
Hakan Serce

Instead of imageElement.src = myImage; you should use window.location = myImage;

And even after that the browser will display the image itself. You can right click and use "Save Link" for downloading the image.

Check this link for more information.


Wow, thanks, that really helped a lot:) But how do you get a pop up save box, so that someone can save to a specific destination (like their Android images folder)?
It depends on the specific browser. Android browser usually download files to a specific folder directly, for instace.
In Chrome this works, but the right-click menu is greyed out. When trying to 'drag' the image out of the browser, Chrome crashes.
groups.google.com/a/chromium.org/forum/#!topic/blink-dev/… Opening data URL like this is going to be blocked it looks like.
B
BigBalli

You cannot use the methods previously mentioned to download an image when running in Cordova. You will need to use the Cordova File Plugin. This will allow you to pick where to save it and leverage different persistence settings. Details here: https://cordova.apache.org/docs/en/latest/reference/cordova-plugin-file/

Alternatively, you can convert the image to base64 then store the string in localStorage but this will fill your quota pretty quickly if you have many images or high-res.


V
Vít Zadina

i create simple typescript function for this purpose, just delete types to use with javascript.

 //ImagePath == canvas.toDataUrl()
private saveImage(imagePath: string, imageName: string ){
    const link = document.createElement('a');
    link.style.display = 'none';
    document.body.appendChild(link)
    link.setAttribute('download', imageName + '.png');
    link.setAttribute('href', imagePath.replace("image/png", "image/octet-stream"));
    link.click();
}

 //function call
 saveImage(canvas.toDataURL(), "myName")

Y
Yogesh Yadav

One can also use element reference to downloaded image:

HTML:

<a download style="display:none" ref="imageDownloadRef"></a>

JAVASCRIPT:

  this.$refs['imageDownloadRef'].href = this.canvas.toDataURL({
  format: 'jpeg',
  quality: 1.0,
  })
  const imageDownloadLink = this.$refs.imageDownloadRef as HTMLElement
  imageDownloadLink.click()

C
Community

@Wardenclyffe and @SColvin, you both are trying to save image using the canvas, not by using canvas's context. both you should try to ctx.toDataURL(); Try This:

var canvas1 = document.getElementById("yourCanvasId");  <br>
var ctx = canvas1.getContext("2d");<br>
var img = new Image();<br>
img.src = ctx.toDataURL('image/png');<br>
ctx.drawImage(img,200,150);<br>

Also you may refer to following links:

http://tutorials.jenkov.com/html5-canvas/todataurl.html

http://www.w3.org/TR/2012/WD-html5-author-20120329/the-canvas-element.html#the-canvas-element


Uncaught TypeError: Object # has no method 'toDataURL'.
This is wrong as the context element doesn't have a toDataURL function: developer.mozilla.org/en-US/docs/Web/API/…. You want to call toDataURL on the canvas element: developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/…