I have following Problem.
I´m using a canvas to resize pictures a user uploaded to my webapp.
Then I retrieve the picture from the canvas as a base64 encoded string and try to upload it to the parse server.
Since parse supports base64 I thought it could work.
When i upload the images however, there is no image but instead this message for every image file i upload:
{"_ContentType":"image/jpg","_ApplicationId":"MY APPLICATION
ID","_JavaScriptKey":"MY JAVASCRIPT
KEY","_ClientVersion":"js1.3.5","_InstallationId":"THE INSTALLATION
ID","_SessionToken":"THE SESSION TOKEN OF THE CURRENT USER"}
I can retrieve the files, but what i get is no image.
Here is my code for uploading the pictures:
var fileUploadControl = $("#product_pictureUploadModal")[0];
if (fileUploadControl.files.length > 0) {
//THE USER SUCCESSFULLY SELECTED A FILE
var file = fileUploadControl.files[0];
if(file.type.match(/image.*/)){
//RESIZE THE IMAGE AND RETURN a base64 STRING
var resizedImage = resizeImage(file);
//CREATE A PARSE FILE
var name = "picture.jpg";
var parseFile = new Parse.File(name, {base64: resizedImage}, "image/jpg");
parseFile.save().then(function() {
//IMAGE SUCCESSFULLY UPLOADED
},
function(error){
alert(error.message);
});
}else{
//THE USER DIDNT CHOSE A PICTURE
}
}else{
//THE USER DIDNT SELECT A FILE
}
Here is my code for resizing the pictures:
function resizeImage(file){
var MAX_WIDTH = 400;
var image = new Image();
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
var url = window.URL || window.webkitURL;
var src = url.createObjectURL(file);
image.src = src;
return image.onload = function(){
ctx.clearRect(0, 0, canvas.width, canvas.height);
if(image.width > MAX_WIDTH){
if(image.width > image.height){
image.height = (image.height%image.width)*400;
}else{
image.height = (image.height/image.width)*400;
}
alert("image height " + image.height);
image.width = 400;
}
canvas.width = image.width;
canvas.height = image.height;
ctx.drawImage(image, 0, 0, image.width, image.height);
url.revokeObjectURL(src);
var fileRezized = encodeURIComponent(canvas.toDataURL("image/jpg"));
return fileRezized;
};
}
What am i missing here?
I hope you guys could help me. I put a lot of work and time in this already and I seem to not get any further than this.
I want to resize the image in the browser because otherwise upload speed might be too slow for some people, as my application will be available for mobile phones as well.
greetins from germany, marvin
When you get no dataURL back from the browser, it's often caused by a cross-domain security violation.
The users image likely does not originate on the same domain as your web page, so when you drawImage the users image to the canvas, you are "tainting" the canvas. This tainting will cause .toDataURL to be disallowed which will in turn cause the DataURL uploaded to your server to be empty.
One workaround
As a workaround, you can "round-trip" the user's image:
upload the users image to your server and save it in the same domain as your web pages.
reload the users browser page along with their image served from your own domain.
Another workaround: FileReader
If your users have modern browsers that support FileReader then you can let your users upload images from their local drives in a security compliant way.
Here's example code using FileReader:
function handleFiles(files) {
for (var i = 0; i < files.length; i++) {
var file = files[i];
var imageType = /image.*/;
if (!file.type.match(imageType)) {
continue;
}
var img = document.createElement("img");
img.classList.add("obj");
img.file = file;
var reader=new FileReader();
reader.onload=(function(aImg){
return function(e) {
aImg.onload=function(){
var canvas=document.createElement("canvas");
var ctx=canvas.getContext("2d");
canvas.width=aImg.width;
canvas.height=aImg.height;
ctx.drawImage(aImg,0,0);
document.body.appendChild(document.createElement('br'));
document.body.appendChild(canvas);
var u=canvas.toDataURL();
var textarea=document.createElement('textarea');
textarea.value=u;
document.body.appendChild(textarea);
}
// e.target.result is a dataURL for the image
aImg.src = e.target.result;
};
})(img);
reader.readAsDataURL(file);
} // end for
} // end handleFiles
//
$("#fileElem").change(function(e){ handleFiles(this.files); });
body{ background-color: ivory; }
canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Example: load images to canvas while satisfying security requirements.</h4>
<input type="file" id="fileElem" multiple accept="image/*">
<br>
There is an error in this line:
var fileRezized = encodeURIComponent(canvas.toDataURL("image/jpg"));
There is no mime-type image/jpg in canvas. This would actually default to image/png instead which I guess could confuse the receiver. Just correct the line to:
var fileRezized = encodeURIComponent(canvas.toDataURL("image/jpeg"));
I don't know parse.com, but also try doing this with this line:
var parseFile = new Parse.File(name, {base64: resizedImage}, "image/jpeg");
// ^^
Test case
var canvas = document.querySelector("canvas"), out = document.querySelector("div");
out.innerHTML = canvas.toDataURL("image/jpg") + "<br><br>"; // PNG
out.innerHTML += canvas.toDataURL("image/jpeg"); // JPEG
<canvas width=1 height=1></canvas><div></div>
Related
I am creating a chrome extension, that saves image urls from previous webpages. Is there any way for me, to upload the images for the user, to a webpages upload section, such as:
Pages upload section
This is what the input html looks like:
<label>
<form>
<input accept="image/*,image/heif,image/heic"
class="mkhogb32" multiple="" type="file">
</form>
</label>
Here is what I have so far:
// load the image
var img = new Image();
img.setAttribute('crossOrigin', 'anonymous');
img.src = result.products[pointer][3];
// loaded
img.onload = function() {
// convert the image into a data url
var dataUrl = getImageDataUrl(img);
var blob = dataUrlToBlob(dataUrl);
console.log(blob);
var form = document.querySelectorAll('form');
var formData = new FormData(form);
formData.append("file", blob, "image_name.png");
var request = new XMLHttpRequest();
// upload
request.open("POST", "/marketplace/create/item");
request.send(formData);
// chrome.storage.local.get( function(result) {
// })
};
//https://scontent-lga3-2.xx.fbcdn.net/v/t1.6435-9/194808255_1211628689294995_1686587396345915188_n.jpg?_nc_cat=107&ccb=1-3&_nc_sid=0d5531&_nc_ohc=mErP2svwNu0AX8Rb0uO&_nc_ht=scontent-lga3-2.xx&oh=c80e70ed525b3a956c4f5c8c70f58048&oe=60E32CCB
// converts an image into a dataurl
function getImageDataUrl(img) {
// Create an empty canvas element
var canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.height;
// Copy the image contents to the canvas
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
// NOTE: this will throw a cross-origin security exception
// if not done in an extension and if the image is cross-origin
return canvas.toDataURL("image/png");
}
// converts a dataurl into a blob
function dataUrlToBlob(dataUrl) {
var binary = atob(dataUrl.split(',')[1]);
var array = [];
for(var i = 0; i < binary.length; i++) {
array.push(binary.charCodeAt(i));
}
return new Blob([new Uint8Array(array)], {type: 'image/png'});
}
I want the images to upload when the user clicks my html injected button on the page. This what I want to happen once my injected html button is clicked:
Send image to webpages server (WORKS FINE)
Here is image showing my image was sent to the pages server: My image uploaded to server
Here is what the image looks like if it were manually added:
Manually uploaded image
Have that image uploaded to facebooks "Add Photos" section. (NO PHOTO IS BEING PREVIEWED ON THE ADD PHOTO SECTION)
Is it possible?
I have a div where users can drag and drop an image and then, using FileReader, I get the base64 of the image. Works fine.
dropper.ondrop = function (e) {
e.preventDefault();
var file = e.dataTransfer.files[0];
var reader = new FileReader();
reader.readAsDataURL(file);
};
My issue is if I have a browser window open and drag and drop an image from the browser I get the error:
Failed to execute 'readAsDataURL' on 'FileReader':
parameter 1 is not of type 'Blob'.
Now, is there any turnaround to get the base64 of an image dragged from the browser window?
Ultimately, is there is a way to get the image URL and then the actual base64 with a server side curl request?
Any idea?
You can use e.dataTransfer.getData('url') to tell whether there's a URL available. Like this:
var url = e.dataTransfer.getData('url');
if(url){
console.log('Url');
console.log(url);
}else{
console.log('File');
var file = e.dataTransfer.files[0];
var reader = new FileReader();
reader.readAsDataURL(file);
}
Then, having the URL, you can load an img element and use draw it on a canvas to grab the base64 representation. Like this:
var img = document.createElement('img');
img.crossOrigin = 'anonymous';
img.onload = function(){
var canvas = document.createElement('canvas');
canvas.width = this.width;
canvas.height = this.height;
var context = canvas.getContext('2d');
context.drawImage(this, 0, 0);
console.log(canvas.toDataURL());
};
img.src = url;
This would be the "final" product:
var dropper = document.querySelector('div');
dropper.ondragover = function(e) {
e.preventDefault();
}
dropper.ondrop = function (e) {
e.preventDefault();
var url = e.dataTransfer.getData('url');
if(url){
console.log('Url');
console.log(url);
var img = document.createElement('img');
img.crossOrigin = 'anonymous';
img.onload = function(){
var canvas = document.createElement('canvas');
canvas.width = this.width;
canvas.height = this.height;
var context = canvas.getContext('2d');
context.drawImage(this, 0, 0);
console.log(canvas.toDataURL());
};
img.src = url;
}else{
console.log('File');
var file = e.dataTransfer.files[0];
var reader = new FileReader();
reader.readAsDataURL(file);
}
};
div{
border:1px solid red;
height:240px;
width:100%;
}
<div>Drop here</div>
Also available here: https://jsfiddle.net/8u6Lprrb/1/
The first parameter comes through with the "http://" or "https://" protocol instead of the expected "file://" protocol. and thats why you cant read it with the HTML5 FILE API, so you may want to download and save the file first before trying to read the contents.
on the other hand, you can update an img tag's src attribute with the retrieved url and skip the readDataAsUrl() portion to hotlink the image.
I have an html canvas that shows a preview of an image when the image is selected in an input. This works in Chrome, but I can't seem to get it to work in Safari. Specifically - in Safari - the onchange="previewFile()" does not seem to call the previewFile function.
<canvas id="canvas" width="0" height="0"></canvas>
<h2>Upload a photo </h2>
<input type="file" onchange="previewFile()"><br>
<script type="text/javascript">
// setup the canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// grab the photo and display in canvas
var photo = new Image();
function previewFile() {
var file = document.querySelector('input[type=file]').files[0];
var reader = new FileReader();
reader.addEventListener("load", function () {
photo.src = reader.result;
canvas.height = photo.height;
canvas.width = photo.width;
ctx.drawImage(photo,0,0);
}, false);
if (file) {
reader.readAsDataURL(file);
}
}
</script>
Your problem is certainly due to the fact that you are not waiting for the image has loaded before you try to draw it on the canvas.
Even wen the source is a dataURI, the loading of the image is asynchronous, so you need to wrap your drawing operations in the image's onload event.
var photo = new Image();
photo.onload = function(){
canvas.height = photo.height;
...
}
...
reader.onload = function(){
// this will eventually trigger the image's onload event
photo.src = this.result;
}
But if all you need is to draw your image on the canvas, don't even use a FileReader, actually, the readAsDataURL() method should trigger a I'm doing something wrong error in your brain. Almost all you can do with a dataURI version of a Blob, you can also do it with the Blob itself, without computing it nor polluting the browser's memory.
For example, to display an image for user input, you can use URL.createObjectURL(blob) method.
// setup the canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// grab the photo and display in canvas
var photo = new Image();
// drawing operations should be in the mage's load event
photo.onload = function() {
// if you don't need to display this image elsewhere
URL.revokeObjectURL(this.src);
canvas.height = this.height;
canvas.width = this.width;
ctx.drawImage(this, 0, 0);
}
photo.onerror = function(e) {
console.warn('file format not recognised as a supported image');
}
file_input.onchange = function() {
// prefer 'this' over DOM selection
var file = this.files[0];
var url = URL.createObjectURL(file);
photo.src = url;
};
<canvas id="canvas" width="0" height="0"></canvas>
<h2>Upload a photo </h2>
<input type="file" id="file_input">
<br>
And for those who need to send this file to their server, use a FormData to send directly the Blob. If you really need a dataURI version, then convert it server-side.
I have a directory with 100 images. I need a copy of them in various folders along with other information that I download from webgl. Hence I want to upload them onto the browser and download them again (hope that isn't stupid)
Here is my code:
var imagefile = model.features[cIndex].imageName.substring(model.features[cIndex].imageName.lastIndexOf('/')+1);
var image = new Image();
image.src = model.imageDirectory + imagefile;
image.onload = function() {
console.info("Read \""+image.src + "\"...Done");
}
image.onerror = function() {
var message = "Unable to open \"" + image.src + "\".";
console.error(message);
alert(message);
}
var data = image.src;
zip.file('image_RH_Original' + cIndex +'.png', data , {base64: true});
Is this wrong? How to I do something similar to "toDataURL" for the image object?
toDataURL is a method of canvas, and webgl draws to a canvas. So just call canvas.toDataURL(). Probably need to set preserveDrawingBuffer to true as well.
I am working on a Web based application where user can create designs in Svg. i want to convert the svg design into png image file on client side. i found a solution of using canvas, this works well in firefox, but in chrome it generate security error.
check the code below thanks:-
var mainsvg=document.getElementById('svgforImg');
var canvas=document.getElementById('canvas');
var ctx = canvas.getContext("2d");
var data=mainsvg.innerHTML;
var DOMURL = self.URL || self.webkitURL || self;
var svg = new Blob([data], {
type: "image/svg+xml;charset=utf-8"
});
var url = DOMURL.createObjectURL(svg);
var img = new Image();
img.onload = function() {
ctx.drawImage(img, 0, 0);
DOMURL.revokeObjectURL(url);
var imageurl = canvas.toDataURL("image/png");
}
Now my variable imageurl contains 'base64 png' image. this works in Firefox. But in chrome line
var imageurl = canvas.toDataURL("image/png");
generate security error.
Any help would be highly appreciated.
I think this is related to this question. From which server does the SVG originate? If it is a different one than the one your application is coming from (remember: sub-domains matter!), you could add the desired http-headers in the originating server.