I am trying to generate a base64 data URL from an image source, but whenever I try to convert it, the dataURL being output is of just the empty canvas without the image. What am I missing here?
src to base64 function:
imageToBase64(url, callback) {
const img = new Image();
img.crossOrigin = 'Anonymous';
img.onload = function () {
let canvas = document.createElement('CANVAS');
const ctx = canvas.getContext('2d');
canvas.height = this.height;
canvas.width = this.width;
ctx.drawImage(this, 0, 0);
const dataURL = canvas.toDataURL('image/png|gif|jpg');
callback(dataURL);
canvas = null;
};
img.src = url;
}
Usage:
componentDidMount() {
this.imageToBase64(this.props.originalUploadFile.data, (dataUrl) => {
console.log(dataUrl) // I am getting a result, but it does not contain the image data
});
}
Related
I use "dom-to-image" to convert html table to png:
var wrapper = document.getElementById('exportContent');
domtoimage.toSvg(wrapper).then(function (svgDataUrl) {
downloadPNGFromAnyImageSrc(svgDataUrl);
});
function downloadPNGFromAnyImageSrc(src)
{
var img = new Image;
img.onload = function(){
var canvas = convertImageToCanvas(img);
var pngImage = convertCanvasToImage(canvas);
var anchor = document.createElement('a');
anchor.setAttribute('href', pngImage.src);
anchor.setAttribute('download', 'image.png');
anchor.click();
};
img.src = src;
// Converts image to canvas; returns new canvas element
function convertImageToCanvas(image) {
var canvas = document.createElement("canvas");
canvas.width = image.width;
canvas.height = image.height;
canvas.getContext("2d").drawImage(image, 0, 0);
return canvas;
}
// Converts canvas to an image
function convertCanvasToImage(canvas) {
var image = new Image();
image.src = canvas.toDataURL("image/png", 1.0);
return image;
}
}
It converts the element to png. However I need to put it into doc file.
Now I need to generate/save a docx file with this png without saving png.
How can I do it?
I followed this post: dom to img
I have to work with pdfmake to build a pdf preview within my laravel application. I am a javascript noob and going nuts to generate the dataURI for an image in b. Hope you can help me out.
How can I get that generated base64 into my docdefinition?
function convertImageToDataURL(src, callback, outputFormat) {
// Create an Image object
var img = new Image();
// Add CORS approval to prevent a tainted canvas
img.crossOrigin = 'Anonymous';
img.onload = function() {
var canvas = document.createElement('CANVAS');
var ctx = canvas.getContext('2d');
var dataURL;
canvas.height = this.naturalHeight;
canvas.width = this.naturalWidth;
ctx.drawImage(this, 0, 0);
dataURL = canvas.toDataURL(outputFormat);
callback(dataURL);
// Mark the canvas to be ready for garbage
// collection
canvas = null;
};
img.src = src;
// make sure the load event fires for cached images too
if (img.complete || img.complete === undefined) {
// Flush cache
img.src = 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==';
// Try again
img.src = src;
}
}
convertImageToDataURL(
'{{asset('storage/'.$report->author->enterprises->first()->logo_image)}}',
function(dataUrl) {
// console.log('RESULT:', dataUrl);
// Put dataUrl into DocDefinition here!?!?
// return dataUrl is undefined
}
);`
Okay. As I said: I am a javascript noob. So I changed the script to this one:
function convertImageToDataURL(imgSrc) {
img = new Image();
img.src = imgSrc;
img.crossOrigin = "Anonymous";
var canvas = document.createElement("canvas");
canvas.width = img.naturalWidth;
canvas.height = img.naturalHeight;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
var dataURL = canvas.toDataURL("image/jpg");
canvas = null;
return dataURL;
}
It might not be beautyful nor elegant, but it works for me.
I'm trying to draw an existing image onto a canvas and encode it via base64. Here is my code:
var canvas = document.createElement("canvas");
canvas.id = "MyCanvas";
document.getElementById("Table1").appendChild(canvas);
var myCanvas = document.getElementById("MyCanvas");
var myCanvasContext = myCanvas.getContext("2d");
myCanvas.width = 135;
myCanvas.height = 170;
var img = new Image();
img.onload = function(){
myCanvasContext.drawImage(img,0,0);
}
img.src = "https://example.com/asd.png";
var toURL = myCanvas.toDataURL();
console.log(toURL);
It draws the image to the canvas, but the toURL is an empty image base64 code with 135x170 size. I've tried to decode it, but it always shows a blank image.
I can't find what is the problem with it.
The problem is that myCanvas.toDataURL(); is called before the image is actually loaded. For this you'd need to move it inside the onload-callback, like:
var img = new Image();
img.onload = function(){
myCanvasContext.drawImage(img,0,0);
// ...moved here
var toURL = myCanvas.toDataURL();
console.log(toURL);
}
img.src = "https://example.com/asd.png";
The following is a simplified example:
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
const img = new Image();
img.crossOrigin = "";
img.src = 'https://www.gravatar.com/avatar/8939f42cb6c31e31e570ea8f07fe9757?s=32&d=identicon&r=PG';
img.onload = () => {
canvas.width = img.naturalWidth;
canvas.height = img.naturalHeight;
ctx.drawImage(img, 0, 0);
console.log(canvas.toDataURL());
};
document.body.appendChild(canvas); // append the canvas ...
document.body.appendChild(img); // ... and img for demo purposes only
var canvas = document.createElement("canvas");
canvas.id = "MyCanvas";
document.getElementById("Table1").appendChild(canvas);
var myCanvas = document.getElementById("MyCanvas");
var myCanvasContext = myCanvas.getContext("2d");
myCanvas.width = 500;
myCanvas.height = 500;
var img = new Image();
img.onload = function(){
myCanvasContext.drawImage(img,0,0);
}
img.src = "http://underthebridge.co.uk/wp-content/uploads/2014/03/Example-main-image1.jpg";
var toURL = myCanvas.toDataURL();
console.log(toURL);
var img2 = document.createElement("img");
img2.id = "MyImg";
img2.src = toURL;
document.getElementById("Table1").appendChild(img2);
<div id='Table1'> </div>
You can't put an base64 inside a canvas but only in a tag img.
I need to read the image data from an image object in javascript.
But my code returns always a blank array (set to 255)
<html>
<header>
</header>
<body>
<input type="file" id="imgfile" onchange="testImageData(event);" />
<canvas id="canvas1" width="640" height="480"></canvas>
<script src="./../scripts/cam.js" ></script>
</body>
</html>
Here is the script
var canvas1 = document.getElementById('canvas1');
var context1 = canvas1.getContext('2d');
function getImageData(image){
/*
returns Uint8ClampedArray object
takes an image obj
*/
var canvas = document.createElement("canvas");
canvas.height = image.height;
canvas.width = image.width;
var ctx = canvas.getContext("2d");
ctx.width = image.width;
ctx.height = image.height;
ctx.drawImage(image,0,0);
return ctx.getImageData(0, 0, ctx.width, ctx.height);
}
function testImageData(event){
var selectedFile = event.target.files[0];
var reader = new FileReader();
var img = new Image();
reader.onload = function(event) {
console.log('onload');
img.src = event.target.result;
img.onload = function(){
context1.drawImage(img, 0,0, img.width, img.height);
var imgData = getImageData(img);
// console.log(imgData);
var data = imgData.data;
for(var i = 0; i<data.length;i+=4){
console.log(data[i],data[i+1],data[i+2],data[i+3]);
}
}
};
In my understanding, the console.log should return me the data in RGBA.
But I'm just getting 255.
console.log output
EDIT:
Okay I found a work around but I don't understand why this is working.
Instead using getImageData, I get the data directly from the drawn context1.
function testImageData(event){
var selectedFile = event.target.files[0];
var reader = new FileReader();
var img = new Image();
reader.onload = function(event) {
console.log('onload');
img.src = event.target.result;
img.onload = function(){
context1.drawImage(img, 0,0, img.width, img.height);
var imgData = context1.getImageData(0,0,img.width,img.height);
var data = imgData.data;
for(var i = 0; i<data.length;i+=4){
console.log(data[i],data[i+1],data[i+2],data[i+3]);
}
}
};
So the problem must lie in creating a new canvas.
You should wait for the image to load img.onload you are waiting for the readers onload event...
you also forget to read the file... missed reader.readAsDataURL
but you don't need the filereader.
window.URL = window.URL || webkitURL
var img = new Image();
img.src = URL.createObjectURL(file)
img.onload = function(){
// put your image on the canvas
}
I am trying to get base64 data from image url but it always return "data:"
Here's the code :
function getBase64Image(imgurl) {
var canvas = document.createElement("canvas");
var img = new Image();
img.src = imgurl;
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
var dataURL = canvas.toDataURL("image/png");
console.log(dataURL);
return dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
}
Use img.onload to execute the code after your image has loaded. Use a callback function to report back the dataURL.
function getBase64Image(imgurl, callback) {
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);
var dataURL = canvas.toDataURL("image/png");
dataURL = dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
if (typeof callback === 'function') {
callback(dataUrl);
}
};
img.src = imgurl;
}