I have an image loaded on my page that I need to convert to base64. I'm currently using the following:
var c = document.createElement("canvas");
var ctx = c.getContext("2d");
var img = document.getElementById("additem_img");
ctx.drawImage(img, 10, 10);
console.log(c.toDataURL());
Which I found in another StackOverflow question. It seems to create a base64 string
data:image/png;base64,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
But when I try to decode this using every online decoder I can, I get nothing. The "additem_img" element is an image who's source is an image from a remote webpage. I want to create a local copy using canvas and base64.
try this:
<img id="additem_img" src="image.png">
<script>
var c = document.createElement("canvas");
var ctx = c.getContext("2d");
var img = document.getElementById("additem_img");
var w = img.width;
var h = img.height;
c.width = w;
c.height = h;
ctx.drawImage(img, 0, 0);
console.log(c.toDataURL());
</script>
Related
Here is my code. I am uploading a image and using like this :
> var canvas = document.createElement('canvas');
> var context = canvas.getContext('2d');
> context.drawImage(image, 0, 0);
This works fine but if I copy the imagedata like below to another canvas. It loads image partially.
var canvas = document.getElementById('myCanvas');
var context1 = canvas.getContext('2d');
context1.putImageData(context.getImageData(0, 0, image.width, image.height), 0, 0);
I tried same approach by creating two canvas and this code which worked fine but without image.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(0, 0, 300, 300);
var d = document.getElementById("myCanvas1");
var btx = d.getContext('2d');
var imgData = ctx.getImageData(0, 0, 300, 300);
btx.putImageData(imgData, 0, 0);
If i create two canvas it works fine but not like the above where I am using in memory canvas.
My HTML file has this :
<canvas id="myCanvas" width="960" height="960"></canvas>
<canvas id="myCanvas1" width="960" height="960"></canvas>
When you create canvases, you need to set their width manually. Default canvas size is 300x150. From here HTMLCanvasElement.
Something like this:
var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
canvas.width = image.width;
canvas.height = image.height;
context.drawImage(image, 0, 0);
To copy one canvas to another use drawImage rather than getImageData, setImageData That way you will use the GPU to move the pixels rather than the CPU. You also have the option to resize, crop, and apply a variety of FXs.
// create a copy of canvasSource
// returns the newly created canvas.
function copyCanvas(canvasSource){
var canvasCopy = document.createElement("canvas");
canvasCopy.width = canvasSource.width;
canvasCopy.height = canvasSource.height;
canvasCopy.getContext("2d").drawImage(canvasSource, 0, 0);
return canvasCopy;
}
I've no idea why this doesn't work. The src attribute of the image is changed with the new data, but the image is not actually visible. I tried with several different images. It's just javascript in a browser and Jquery is required.
<body>
<img src="" id="test">
</body>
<script>
const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
let img = new Image();
img.onload = getIt
img.src = 'download.png';
function getIt() {
canvas.width = this.width;
canvas.height = this.height;
const imageData = ctx.getImageData(0, 0, this.width, this.height);
ctx.drawImage(this, canvas.width , canvas.height);
ctx.putImageData(imageData, canvas.width, canvas.height);
$('#test').get(0).src = canvas.toDataURL("image/png");
}
</script>
I tried with several different images, all png. At the moment this is the entire code for the project so I don't foresee anything that could be interfering with it.
The result is this but the image cannot be seen:
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABIAAAAeCAYAAAAhDE4sAAAAMklEQVRIS+3SsQ0A....etc" id="test">
EDIT: It seems like it might be getting the data from the image incorrectly but I've no idea why...I mean why would it get the data but be incomplete or incorrect?
Please try this:
(You don't need to get or put the image data)
Also you were doing this:ctx.putImageData(imageData, canvas.width, canvas.height);. This means that you are drawing the image totally outside the canvas. Do this instead: ctx.putImageData(imageData, 0,0);
const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
let img = new Image();
img.onload = getIt
img.src = "download.png";
function getIt() {
canvas.width = this.width;
canvas.height = this.height;
//draw the image onto the canvas
ctx.drawImage(this, 0,0);
//use the data uri
test.src = canvas.toDataURL("image/png");
}
<img src="" id="test">
I want to convert image to base64 but the value is not complete?
<img crossorigin="anonymous" id="imageid" src="{{helper.photo_1}}" />
function getBase64Image(img) {
var canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
var dataURL = canvas.toDataURL("image/png");
return dataURL
}
var base64 = getBase64Image(document.getElementById("imageid"));
console.log(base64); // the value is not complete.
When I use the base64 to show image, this is what it looks like:
I'm trying to learn manipulate image and canvas in javascript. I'm wondering why we can not do :
var urlimg='http://images.aviary.com/imagesv5/feather_default.jpg';
var can = document.getElementById('canvas');
var ctx = can.getContext('2d');
var img = new Image();
img.onload = function(){
}
img.src =urlimg ;
can.width = img.width;
can.height = img.height;
ctx.drawImage(img, 0, 0, img.width, img.height);
$('#image1').attr('src', img.src);
And we have to do this :
var urlimg='http://images.aviary.com/imagesv5/feather_default.jpg';
var can = document.getElementById('canvas');
var ctx = can.getContext('2d');
var img = new Image();
img.onload = function(){
can.width = img.width;
can.height = img.height;
ctx.drawImage(img, 0, 0, img.width, img.height);
}
img.src =urlimg ;
$('#image1').attr('src', img.src);
Is it due to time of image to load ?
Can I create a canvas from an existing object image ?
Thanks.
Is it due to time of image to load ?
Yes in part, but mostly because image loading is asynchronous so the next lines of code are executed right away while the image is loaded. To let you know an event is raised when it's done.
Can I create a canvas from an existing object image ?
No (not directly), but you can draw the image onto a canvas to initialize it (as you already do):
ctx.drawImage(imageElement, 0, 0, width, height);
I have created a canvas with document.createElement("canvas"):
var canvas = document.createElement("canvas");
canvas.width = width; // width = 4000 or more
canvas.height = height; // height = 5000 or more
Then I use canvas.toDataURL() to get its base64 string:
var str = canvas.toDataURL();
but the 'str' sometimes returns as "data:,", with no image data in it. Just those six chars.
Sometimes it returns the correct string like "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAEGgAABPsCAYAAABg/aH3AAAgAElEQVR4XuzcQREAAAjDM..."
I the canvas.width is too large ....
You should try to create a 2D context explicitly and then draw in it an empty shape, something like:
var canvas = document.createElement("canvas");
canvas.width = 4000;
canvas.height = 5000;
var ctx=canvas.getContext('2d');
ctx.fillRect(0,0,0,0);
canvas.toDataURL();
Edit: It seems that your canvas contains too much data to be exported as a dataUri:
var canvas = document.createElement("canvas");
canvas.width = 400000000;
canvas.height = 500000000;
var ctx=canvas.getContext('2d');
ctx.fillRect(0,0,0,0);
canvas.toDataURL();
// outputs : "data:,"