I'm converting images to base64 using canvas. What i need to do is convert those images and then show the result to the user (original image and base64 version). Everything works as expected with small images, but when i try to convert large images (>3MB) and the conversion time increases, the base64 version is empty.
This might be is caused because the result is shown before the toDataURL() function is completed.
I need to show the result after all the needed processing has ended, for testing purposes.
Here's my code:
var convertToBase64 = function(url, callback)
{
var image = new Image();
image.onload = function ()
{
//create canvas and draw image...
var imageData = canvas.toDataURL('image/png');
callback(imageData);
};
image.src = url;
};
convertToBase64('img/circle.png', function(imageData)
{
window.open(imageData);
});
Even though i'm using image.onload() with a callback, i'm unable to show the result after the toDataURL() has been processed.
What am i doing wrong?
UPDATE: I tried both the solutions below and they didn't work. I'm using AngularJS and Electron in this project. Any way i can force the code to be synchronous? Or maybe some solution using Promises?
UPDATE #2: #Kaiido pointed out that toDataURL() is in fact synchronous and this issue is more likely due to maximum URI length. Since i'm using Electron and the image preview was for testing purposes only, i'm going to save the file in a folder and analise it from there.
Your code seems absolutely fine. Not sure why isn't working you. Maybe, there are some issues with your browser. Perhaps try using a different one. Also you could use a custom event, which gets triggered when the image conversion is competed.
// using jQuery for custom event
function convertToBase64(url) {
var image = new Image();
image.src = url;
image.onload = function() {
var canvas = document.createElement('canvas');
canvas.width = image.width;
canvas.height = image.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(image, 0, 0);
var imageData = canvas.toDataURL();
$(document).trigger('conversionCompleted', imageData);
};
};
convertToBase64('4mb.jpg');
$(document).on('conversionCompleted', function(e, d) {
window.open(d);
});
This approach might work for you. It shows the image onscreen using the native html element, then draws it to a canvas, then converts the canvas to Base64, then clears the canvas and draws the converted image onto the canvas. You can then scroll between the top image (original) and the bottom image (converted). I tried it on large images and it takes a second or two for the second image to draw but it seems to work...
Html is here:
<img id="imageID">
<canvas id="myCanvas" style="width:400;height:400;">
</canvas>
Script is here:
var ctx;
function convertToBase64(url, callback)
{
var image = document.getElementById("imageID");
image.onload = function() {
var canvas = document.getElementById("myCanvas");
canvas.width = image.naturalWidth;
canvas.height = image.naturalHeight;
ctx = canvas.getContext("2d");
ctx.drawImage(image,0,0);
var imageData = canvas.toDataURL('image/png');
ctx.fillStyle ="#FFFFFF";
ctx.fillRect(0,0,canvas.width,canvas.height);
callback(imageData);
};
image.src = url;
};
var imagename = 'images/bigfiletest.jpg';
window.onload = function () {
convertToBase64(imagename, function(imageData) {
var myImage = new Image();
myImage.src = imageData;
ctx.drawImage(myImage,0,0);
});
}
Note that I also tried it without the callback and it worked fine as well...
Related
The question on a single line:
Is there a toDataURL method working on a <IMG> element?
Most of the people seem to be interested in how to get an IMG from a CANVAS, but I need the opposite.
Why? I need to use the toDataURL() method on the IMG.
So, this is the pseudo code that I wish existed in reality:
var img = document.getElementById('myImage');
var canvas = img.getCanvasFromImage();
var dataURL = canvas.toDataURL();
Is there already a method, or a workaround (e.g. creating an empty canvas, copying the IMG on top, etc.) to do the getCanvasFromImage? I couldn't find one.
Some more details WHY, but there is no need to read further. I am using the VIDEO tag to get the camera stream, and when the user clicks a button, I copy the CANVAS to the IMG.
But since I do not want to show the whole picture while taking a photo (I want it to be consistent over different devices, regardless of the camera resolution, keeping a 16:9 aspect ratio), I only show a portion of the image using object-fit: cover; .
So, now I have a "partial" image, but if I do a toDataURL on the canvas I have, it gives me the WHOLE picture, regardless of the "object-fit" value.
If this is not clear, no problem :) I only need a "toDataURL" method working on a <IMG> element :)
HTMLImageElement.prototype.getCanvasFromImage = function(){
const canvas = document.createElement('canvas');
canvas.width = this.width;
canvas.height = this.height;
const ctx = canvas.getContext('2d');
ctx.drawImage(this, 0, 0);
return canvas;
};
const img = document.getElementById('myImage');
img.onload = () => {
const canvas = img.getCanvasFromImage();
const dataURL = canvas.toDataURL();
console.log(dataURL);
}
<img id="myImage" crossorigin="anonymous" src="https://dl.dropbox.com/s/zpoxft30lzrr5mg/20201012_102150.jpg" />
Its work, but please READ THIS. Better way is create pure function and pass image as argument:
function getCanvasFromImage(image) {
const canvas = document.createElement('canvas');
canvas.width = image.width;
canvas.height = image.height;
const ctx = canvas.getContext('2d');
ctx.drawImage(image, 0, 0);
return canvas;
}
I have an image that is being shown in a Chrome App and is from a remote site. I want to be able to save the image locally in case network connection is unavailable.
I've been researching and found some APIs that might help me such as chrome.fileSystem, however, there aren't any simple examples like this.
Would someone be able to provide me with a simple example on how to do this?
It is preferred if the user doesn't have to press save or anything, having the downloading happen in the background. The image changes at random so I need this to be automated if possible.
what about storing it in localStorage?
var image = document.getElementById('bannerImg');
imgData = getBase64Image(image);
localStorage.setItem("imgData", imgData);
then to restore (adapted from this answer):
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.replace(/^data:image\/(png|jpg);base64,/, "");
}
var dataImage = localStorage.getItem('imgData');
bannerImg = document.getElementById('tableBanner');
bannerImg.src = "data:image/png;base64," + dataImage;
I am making a chrome extension that uses the chrome.tabs.captureVisibleTab method to grab a screencap of the current tab and then displays that in a popup from the chrome extension. If I use the img tag and use the data coming from the chrome function, such as data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAMCAgMCAgMDAwMEAwME…UUUAFFFFABRRRQAUUUUAFFFFABRRRQAUUUUAFFFFABRRRQAUUUUAFFFFABRRRQAUUUUAf/2Q==, the <img> displays pixel perfect, it is crisp and that's what I want. Problem is that I need to make it into a canvas, and when I do that, it becomes blurry.
This is a screencap of the <img> that uses the link data provided by Google to be used as a comparison to the canvas which is below.
This is the blurry canvas.
This is the code that I am using to try to do this, but I can't figure out how to make the canvas crisp like the image.
chrome.runtime.sendMessage({msg: "capture"}, function(response) {
console.log(response.imgSrc);
var img = document.createElement('img');
var _canvas = document.createElement("canvas");
img.src = response.imgSrc;
img.height = 436;
img.width = 800;
document.getElementById('main-canvas').appendChild(img);
draw(response);
});
function draw(response) {
var canvas = document.getElementById('imageCanvas');
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
//Get a 2d context
var ctx = canvas.getContext('2d');
//use image to paint canvas
var _image = new Image();
_image.onload = function() {
ctx.drawImage(_image, 0, 0, 800, 436);
}
_image.src = response.imgSrc;
document.getElementById('main-canvas').appendChild(canvas);
}
This is what I used to fix my problem: High Resolution Canvas from HTML5Rocks
I've tried all code variations that are online. I just want to display an image on a canvas. I've tried code from this site.
window.onLoad=function(){
function draw(){
var ctx = document.getElementById("canvas1").getContext("2d");
var img = new Image();
img.src = 'images/ball.png';
img.onload = function(){
ctx.drawImage(img,0,0);
};
};
};
It's not the file path that's a problem, that has been tested without the images folder. There are no errors in the console. Thanks.
One search in google and there you go with complete jsfiddle example:
// Grab the Canvas and Drawing Context
var canvas = document.getElementById('c');
var ctx = canvas.getContext('2d');
// Create an image element
var img = document.createElement('IMG');
// When the image is loaded, draw it
img.onload = function () {
ctx.drawImage(img, 0, 0);
}
// Specify the src to load the image
img.src = "http://i.imgur.com/gwlPu.jpg";
http://jsfiddle.net/jimrhoskins/Sv87G/
I have the following code :
function createImage(source) {
var pastedImage = new Image();
pastedImage.onload = function() {
document.write('<br><br><br>Image: <img src="'+pastedImage.src+'" height="700" width="700"/>');
}
pastedImage.src = source;
}
Here I am displaying the image through html image tag which I wrote in document.write and provide appropriate height and width to image.
My question is can it possible to displaying image into the canvas instead of html img tag? So that I can drag and crop that image as I want?
But how can I display it in canvas?
Further I want to implement save that image using PHP but for now let me know about previous issue.
Try This
var ctx = document.getElementById('canvas').getContext('2d');
var img = new Image(); // Create new img element
img.onload = function(){
// execute drawImage statements here This is essential as it waits till image is loaded before drawing it.
ctx.drawImage(img , 0, 0);
};
img.src = 'myImage.png'; // Set source path
Make sure the image is hosted in same domain as your site. Read this for Javascript Security Restrictions Same Origin Policy.
E.g. If your site is http://example.com/
then the Image should be hosted on http://example.com/../myImage.png
if you try http://facebook.com/..image/ or something then it will throw security error.
Use
CanvasRenderingContext2D.drawImage.
function createImage(source) {
var ctx = document.getElementById('canvas').getContext('2d');
var pastedImage = new Image();
pastedImage.onload = function(){
ctx.drawImage(pastedImage, 0, 0);
};
pastedImage = source;
}
Also MDN seems to be have nice examples.