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Once I have a base64 url how can I change the filter for brightness and contrast?

If I have an image in base64 ex.
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAABDAAwfqNRk/rjcYX+PxrV/wtWqwJSTlboMgAAAABJRU5ErkJggg==
What's the fastest way to change a filter (ex. brightness, contrast) programmatically and without creating any img or canvas tag in the view? Then once changed, convert it back to a base64 url?

You can do this by putting the image onto a HTML canvas with filters applied, then turning that canvas back into a base64 URL.
Since you never add the canvas to the document, it will never be seen.
This is how you would do it asynchronously:
This takes about 1-10ms
function applyFiltersToImage(imageURL, callBack) {
// load the image url into an image object
const image = new Image();
image.src = imageURL;
const canvas = document.createElement("canvas");
const ctx = canvas.getContext('2d');
image.onload = () => {
canvas.width = image.width;
canvas.height = image.height;
// apply css filters here
ctx.filter = 'brightness(0.5) contrast(2)';
ctx.drawImage(image, 0, 0, canvas.width, canvas.height);
// turn canvas back into a base64 image URL
callBack(canvas.toDataURL("image/png"));
}
}
You could do it synchronously if you already have the Image instance loaded.
This is how you will do it synchronously:
function applyFiltersToImageSync(imageObject) {
const canvas = document.createElement("canvas");
const ctx = canvas.getContext('2d');
canvas.width = imageObject.width;
canvas.height = imageObject.height;
// apply css filters here
ctx.filter = 'brightness(0.5) contrast(2)';
ctx.drawImage(imageObject, 0, 0, canvas.width, canvas.height);
//turn canvas back into a base64 image
return canvas.toDataURL("image/png");
}

How to convert a locally stored image to base64?

I have an image path which it is stored locally.
For example,
let path = 'C:\Users\Jonnie\Desktop'
How do I get the image by using JavaScript only and convert it to base64?

function imageToBase64(img)
{
var canvas, ctx, dataURL, base64;
canvas = document.createElement("canvas");
ctx = canvas.getContext("2d");
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0);
dataURL = canvas.toDataURL("image/png");
base64 = dataURL.replace(/^data:image\/png;base64,/, "");
return base64;
}
source
Now you just need to pass your image to there

You can use <canvas> for this.
Create a canvas and load in the image then use toDataURL() to get it in base64
The documentation for <canvas> can be found here

Can't get base64 resized image from javascript canvas

I have two main questions. I'm trying to resize a base64 image according to the answer in
JavaScript reduce the size and quality of image with based64 encoded code
This seemed simple enough, except for the fact that I need to get only the base64 string from that function, without the data:image... header.
I tried to modify the function like this:
function resizeBase64Img(base64, width, height) {
var canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;
var context = canvas.getContext("2d");
var deferred = $.Deferred();
$("<img/>").attr("src", "data:image/gif;base64," + base64).load(function () {
context.scale(width / this.width, height / this.height);
context.drawImage(this, 0, 0);
deferred.resolve($("<img/>").attr("src", canvas.toDataURL()));
});
var result = canvas.toDataURL();
return result.substr(result.indexOf(",") + 1)
}
which returns a base64 string. This string is corrupted, and it never displays correctly. Why is this happening and how can I fix it?
The other question is, is there a way to resize the image based on percentage and not on pixel size?
Thanks

I ended up rewriting the function based on another canvas function I found. This function takes the src of a base64 img, modifies the size and assigns the result in base64 to another element:
function resizeBase64Img(url, width, height) {
var img = new Image();
img.setAttribute('crossOrigin', 'anonymous');
img.onload = function () {
var canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;
var ctx = canvas.getContext("2d");
ctx.scale(width/this.width, height/this.height);
ctx.drawImage(this, 0, 0);
result=canvas.toDataURL();
$('#ASSIGNEDELEMENT').val(result.substr(result.indexOf(",") + 1));
};
img.src = url;
}
And it should be invoked like this:
resizeBase64Img($('#image').attr('src'),300,300);

Image not getting copied properly in javascript

I need images to be copied and sent to server for image rotations etc.
To copy an image I'm using this code( from Get image data in JavaScript?):
function getBase64Image(img) {
// Create an empty canvas element
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");
var replaced = dataURL.replace(/^data:image\/(png|jpg);base64,/, "");
console.log("dataurl=",dataURL);
console.log("replaced=",replaced);
return replaced;
}
It is called like this:
$("#xyz").load(send_image).each(function () {
if (this.complete)
$(this).load();
});
function send_image(){
getBase64Image(document.getElementById('xyz'));
}
However in getBase64Image function once in 40-50 times dataURL is being returned as empty.
What could be the reason?

Saving GIF into base64 string using Canvas HTML5 javascript

I have been trying to convert images to base64 string in Javascript. So far with this code which I found on stackoverflow I was able to convert jpeg and png images to their respective base64 strings. But when i try to convert GIF into a base64 it does conversion but the string always have :
data:image/png;base64,............................<string continues>
and when i try to open that, gif image doesn't work.
It should be:
data:image/gif;base64,............................<string continues>
Here's the code:
function convertImgToBase64(url,callback,outputFormat){
var canvas = document.createElement('CANVAS'),
ctx = canvas.getContext('2d'),
img = new Image;
img.crossOrigin = 'Anonymous';
img.onload = function(){
var dataURL;
canvas.height = img.height;
canvas.width = img.width;
ctx.drawImage(img,0,0);
dataURL = canvas.toDataURL(outputFormat || 'image/png');
callback.call(this, dataURL);
canvas = null;
};
img.src = url;
}
I am passing the image from a url for example take : http://www.howtogeek.com/wp-content/uploads/2010/10/DANCING_BABY.gif
Please help.