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How to change size of pixel square using createImageData in html canvas? [duplicate]

I have a canvas in my webpage; I create a new Image data in this canvas then I modify some pixel through myImgData.data[] array. Now I would like to scale this image and make it bigger. I tried by scaling the context but the image remains small. Is it possible to do this?
Thanks

You could draw the imageData to a new canvas, scale the original canvas and then draw the new canvas to the original canvas.
Something like this should work:
var imageData = context.getImageData(0, 0, 100, 100);
var newCanvas = $("<canvas>")
.attr("width", imageData.width)
.attr("height", imageData.height)[0];
newCanvas.getContext("2d").putImageData(imageData, 0, 0);
context.scale(1.5, 1.5);
context.drawImage(newCanvas, 0, 0);
Here's a functioning demo http://jsfiddle.net/Hm2xq/2/.

I needed to do it without the interpolation that putImageData() causes, so I did it by scaling the image data into a new, resized ImageData object. I can't think of any other time I've thought that using 5 nested for loops was a good idea:
function scaleImageData(imageData, scale) {
var scaled = c.createImageData(imageData.width * scale, imageData.height * scale);
for(var row = 0; row < imageData.height; row++) {
for(var col = 0; col < imageData.width; col++) {
var sourcePixel = [
imageData.data[(row * imageData.width + col) * 4 + 0],
imageData.data[(row * imageData.width + col) * 4 + 1],
imageData.data[(row * imageData.width + col) * 4 + 2],
imageData.data[(row * imageData.width + col) * 4 + 3]
];
for(var y = 0; y < scale; y++) {
var destRow = row * scale + y;
for(var x = 0; x < scale; x++) {
var destCol = col * scale + x;
for(var i = 0; i < 4; i++) {
scaled.data[(destRow * scaled.width + destCol) * 4 + i] =
sourcePixel[i];
}
}
}
}
}
return scaled;
}
I hope that at least one other programmer can copy and paste this into their editor while muttering, "There but for the grace of god go I."

I know it's an old subject, but since people like may find it useful, I add my optimization to the code of rodarmor :
function scaleImageData(imageData, scale) {
var scaled = ctx.createImageData(imageData.width * scale, imageData.height * scale);
var subLine = ctx.createImageData(scale, 1).data
for (var row = 0; row < imageData.height; row++) {
for (var col = 0; col < imageData.width; col++) {
var sourcePixel = imageData.data.subarray(
(row * imageData.width + col) * 4,
(row * imageData.width + col) * 4 + 4
);
for (var x = 0; x < scale; x++) subLine.set(sourcePixel, x*4)
for (var y = 0; y < scale; y++) {
var destRow = row * scale + y;
var destCol = col * scale;
scaled.data.set(subLine, (destRow * scaled.width + destCol) * 4)
}
}
}
return scaled;
}
This code uses less loops and runs roughly 30 times faster. For instance, on a 100x zoom of a 100*100 area this codes takes 250 ms while the other takes more than 8 seconds.

You can scale the canvas using the drawImage method.
context = canvas.getContext('2d');
context.drawImage( canvas, 0, 0, 2*canvas.width, 2*canvas.height );
This would scale the image to double the size and render the north-west part of it to the canvas. Scaling is achieved with the third and fourth parameters to the drawImage method, which specify the resulting width and height of the image.
See docs at MDN https://developer.mozilla.org/en-US/docs/DOM/CanvasRenderingContext2D#drawImage%28%29

#Castrohenge's answer works, but as Muhammad Umer points out, it messes up the mouse coordinates on the original canvas after that. If you want to maintain the ability to perform additional scales (for cropping, etc.) then you need to utilize a second canvas (for scaling) and then fetch the image data from the second canvas and put that into the original canvas. Like so:
function scaleImageData(imageData, scale){
var newCanvas = $("<canvas>")
.attr("width", imageData.width)
.attr("height", imageData.height)[0];
newCanvas.getContext("2d").putImageData(imageData, 0, 0);
// Second canvas, for scaling
var scaleCanvas = $("<canvas>")
.attr("width", canvas.width)
.attr("height", canvas.height)[0];
var scaleCtx = scaleCanvas.getContext("2d");
scaleCtx.scale(scale, scale);
scaleCtx.drawImage(newCanvas, 0, 0);
var scaledImageData = scaleCtx.getImageData(0, 0, scaleCanvas.width, scaleCanvas.height);
return scaledImageData;
}

Nowadays, the best way to render a scaled ImageData object is generally to create an ImageBitmap from it.
All modern browsers finally do support it.
This will use a faster path to render the ImageData's content to a bitmap readily available to be painted by drawImage(), theoretically a lot faster than the second best option of putting the ImageData on a secondary <canvas> and redraw that <canvas>.
The main catch-up is that createImageBitmap() is asynchronous*, and thus it may not fit in an animation frame very well.
(async () => {
// here I'll just make some noise in my ImageData
const imagedata = new ImageData(100, 100);
const arr = new Uint32Array(imagedata.data.buffer);
for( let i = 0; i < arr.length; i++ ) {
arr[i] = Math.random() * 0xFFFFFF + 0xFF000000;
}
// now to render it bigger
const bitmap = await createImageBitmap(imagedata);
const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
ctx.imageSmoothingEnabled = false; // keep pixel perfect
ctx.drawImage(bitmap, 0, 0, canvas.width, canvas.height);
})();
<canvas width="1000" height="1000"></canvas>
* Technically, only Firefox does implement createImageBitmap(<ImageData>) asynchronously, Chrome and Safari will resolve the returned Promise synchronously, and there, it's safe to use it in an animation frame: https://jsfiddle.net/vraz3xcg/

JavaScript - Generate random pixels on HTML5 canvas

I want to create a random generated image (random colors), like this one. But, I want to do it in javascript, but for some reason I am getting black screen.
Here is my code:
var g=document . createElement( 'canvas').getContext('2d');
g.canvas.width=g.canvas.height = 800;
g.imgd = g.getImageData(0, 0, 800, 800);
g.data = g.imgd.data;
g.data.forEach((_, index) => (index & 3) < 3 && (g.data[index] = Math.random()));
g.putImageData(g.imgd, 0, 0);
document.body.appendChild(g.canvas);;;
And i am getting black screen, and on some websites it is white screen. So what is what not working in my script? My english is not very good, but can someone explain what is wrong, my code dont'esnt working.
I also tried different dimensions of canvas and I dont see any errors so what is wrong?

You are using Math.random() which generates floats from 0 to 1 without including 1. Since you're applying zeroes to the color components (the data from getImageData().data), you get the color black (rgb(0, 0, 0)).
Here's a more readable solution:
var canvas = document.createElement('canvas');
canvas.width = canvas.height = 800;
var ctx = canvas.getContext('2d');
var imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);
function randomInt(min, max) {
return Math.floor(Math.random() * (max - min + 1)) + min;
}
for (var i = 0; i < imgData.data.length; i += 4) {
imgData.data[i] = randomInt(0, 255); // red
imgData.data[i+1] = randomInt(0, 255); // green
imgData.data[i+2] = randomInt(0, 255); // blue
imgData.data[i+3] = 255; // alpha
}
ctx.putImageData(imgData, 0, 0);
document.body.appendChild(canvas);

Math.random() returns a floating point number, not within the full range of 0-255. You can alternatively use .fillStyle() and set the color to a random hex color.
function pixels(width = 100, height = 100, size = 1, canvas) {
var canvas = canvas || document.createElement("canvas");
var ctx = canvas.getContext("2d");
var total = [];
canvas.width = width;
canvas.height = height;
function random() {
return "XXXXXX".replace(/X/g, function() {
var seed = "a0b1c2d3e4f56789";
return seed.charAt(Math.floor(Math.random() * seed.length))
})
};
for (var x = 0; x <= width; x += size) {
total.push(x)
};
total.forEach(function(value, index) {
for (var i = 0; i <= height; i++) {
ctx.fillStyle = "#" + random();
ctx.fillRect(value, total[i], size, size);
}
});
document.body.appendChild(canvas);
return ctx;
};
var c = pixels(window.innerWidth - 20, window.innerHeight - 20);

Animating canvas to look like tv noise

I have a function named generateNoise() which creates a canvas element and paints random RGBA values to it; which, gives the appearance of noise.
My Question
What would be the best way to infinitely animate the noise to give the appearance of movement. So that it may have more life?
JSFiddle
function generateNoise(opacity) {
if(!!!document.createElement('canvas').getContext) {
return false;
}
var canvas = document.createElement('canvas'),
ctx = canvas.getContext('2d'),
x,y,
r,g,b,
opacity = opacity || .2;
canvas.width = 55;
canvas.height = 55;
for (x = 0; x < canvas.width; x++){
for (y = 0; y < canvas.height; y++){
r = Math.floor(Math.random() * 255);
g = Math.floor(Math.random() * 255);
b = Math.floor(Math.random() * 255);
ctx.fillStyle = 'rgba(' + r + ',' + b + ',' + g + ',' + opacity + ')';
ctx.fillRect(x,y,1,1);
}
}
document.body.style.backgroundImage = "url(" + canvas.toDataURL("image/png") + ")";
}
generateNoise(.8);

Update 1/2017: I rewrote the entire answer as it started to become rather messy, and to address some of the issues pointed out in the comments. The original answer can be found here. The new answer has in essence the same code but improved, and with a couple of new techniques, one utilizes a new feature available since this answer was first posted.
For a "true" random look we would need to use pixel-level rendering. We can optimize this using 32-bit unsigned buffers instead of 8-bit, and we can also turn off the alpha-channel in more recent browsers which speeds up the entire process (for older browsers we can simply set a black opaque background for the canvas element).
We create a reusable ImageData object once outside the main loop so the main cost is only putImageData() and not both inside the loop.
var ctx = c.getContext("2d", {alpha: false}); // context without alpha channel.
var idata = ctx.createImageData(c.width, c.height); // create image data
var buffer32 = new Uint32Array(idata.data.buffer); // get 32-bit view
(function loop() {
noise(ctx);
requestAnimationFrame(loop)
})()
function noise(ctx) {
var len = buffer32.length - 1;
while(len--) buffer32[len] = Math.random() < 0.5 ? 0 : -1>>0;
ctx.putImageData(idata, 0, 0);
}
/* for browsers wo/2d alpha disable support */
#c {background:#000}
<canvas id=c width=640 height=320></canvas>
A very efficient way, at the cost of some memory but reduced cost on the CPU, is to pre-render a larger off-screen canvas with the noise once, then place that canvas into the main one using random integer offsets.
It require a few extra preparation steps but the loop can run entirely on the GPU.
var w = c.width;
var h = c.height;
var ocanvas = document.createElement("canvas"); // create off-screen canvas
ocanvas.width = w<<1; // set offscreen canvas x2 size
ocanvas.height = h<<1;
var octx = ocanvas.getContext("2d", {alpha: false});
var idata = octx.createImageData(ocanvas.width, ocanvas.height);
var buffer32 = new Uint32Array(idata.data.buffer); // get 32-bit view
// render noise once, to the offscreen-canvas
noise(octx);
// main loop draw the offscreen canvas to random offsets
var ctx = c.getContext("2d", {alpha: false});
(function loop() {
var x = (w * Math.random())|0; // force integer values for position
var y = (h * Math.random())|0;
ctx.drawImage(ocanvas, -x, -y); // draw static noise (pun intended)
requestAnimationFrame(loop)
})()
function noise(ctx) {
var len = buffer32.length - 1;
while(len--) buffer32[len] = Math.random() < 0.5 ? 0 : -1>>0;
ctx.putImageData(idata, 0, 0);
}
/* for browsers wo/2d alpha disable support */
#c {background:#000}
<canvas id=c width=640 height=320></canvas>
Do note though that with the latter technique you may risk getting "freezes" where the new random offset is similar to the previous one. To work around this problem, set criteria for the random position to disallow too close positions in a row.

I tried to make a similar function a while ago. I set each pixel random value, and in addition to that, I overlayed a sinusodial wave that traveled upwards with time just to make it look more realistic. You can play with the constants in the wave to get different effects.
var canvas = null;
var context = null;
var time = 0;
var intervalId = 0;
var makeNoise = function() {
var imgd = context.createImageData(canvas.width, canvas.height);
var pix = imgd.data;
for (var i = 0, n = pix.length; i < n; i += 4) {
var c = 7 + Math.sin(i/50000 + time/7); // A sine wave of the form sin(ax + bt)
pix[i] = pix[i+1] = pix[i+2] = 40 * Math.random() * c; // Set a random gray
pix[i+3] = 255; // 100% opaque
}
context.putImageData(imgd, 0, 0);
time = (time + 1) % canvas.height;
}
var setup = function() {
canvas = document.getElementById("tv");
context = canvas.getContext("2d");
}
setup();
intervalId = setInterval(makeNoise, 50);
<canvas id="tv" width="400" height="300"></canvas>
I used it as a preloader on a site. I also added a volume rocker as a loading bar, here's a screenshot:

I re-wrote your code so each step is separate so you can re-use things without having to create and re-create each time, reduced in-loop calls and hopefully made it clear enough to be able to follow by reading it.
function generateNoise(opacity, h, w) {
function makeCanvas(h, w) {
var canvas = document.createElement('canvas');
canvas.height = h;
canvas.width = w;
return canvas;
}
function randomise(data, opacity) { // see prev. revision for 8-bit
var i, x;
for (i = 0; i < data.length; ++i) {
x = Math.floor(Math.random() * 0xffffff); // random RGB
data[i] = x | opacity; // set all of RGBA for pixel in one go
}
}
function initialise(opacity, h, w) {
var canvas = makeCanvas(h, w),
context = canvas.getContext('2d'),
image = context.createImageData(h, w),
data = new Uint32Array(image.data.buffer);
opacity = Math.floor(opacity * 0x255) << 24; // make bitwise OR-able
return function () {
randomise(data, opacity); // could be in-place for less overhead
context.putImageData(image, 0, 0);
// you may want to consider other ways of setting the canvas
// as the background so you can take this out of the loop, too
document.body.style.backgroundImage = "url(" + canvas.toDataURL("image/png") + ")";
};
}
return initialise(opacity || 0.2, h || 55, w || 55);
}
Now you can create some interval or timeout loop which keeps re-invoking the generated function.
window.setInterval(
generateNoise(.8, 200, 200),
100
);
Or with requestAnimationFrame as in Ken's answer
var noise = generateNoise(.8, 200, 200);
(function loop() {
noise();
requestAnimationFrame(loop);
})();
DEMO

Ken's answer looked pretty good, but after looking at some videos of real TV static, I had some ideas and here's what I came up with (two versions):
http://jsfiddle.net/2bzqs/
http://jsfiddle.net/EnQKm/
Summary of changes:
Instead of every pixel being independently assigned a color, a run of multiple pixels will get a single color, so you get these short, variable-sized horizontal lines.
I apply a gamma curve (with the Math.pow) to bias the color toward black a little.
I don't apply the gamma in a "band" area to simulate the banding.
Here's the main part of the code:
var w = ctx.canvas.width,
h = ctx.canvas.height,
idata = ctx.createImageData(w, h),
buffer32 = new Uint32Array(idata.data.buffer),
len = buffer32.length,
run = 0,
color = 0,
m = Math.random() * 6 + 4,
band = Math.random() * 256 * 256,
p = 0,
i = 0;
for (; i < len;) {
if (run < 0) {
run = m * Math.random();
p = Math.pow(Math.random(), 0.4);
if (i > band && i < band + 48 * 256) {
p = Math.random();
}
color = (255 * p) << 24;
}
run -= 1;
buffer32[i++] = color;
}

I happen to have just written a script that does just this, by getting the pixels from a black canvas and just altering random alpha values and using putImageData
Result can be found at http://mouseroot.github.io/Video/index.html
var currentAnimationFunction = staticScreen
var screenObject = document.getElementById("screen").getContext("2d");
var pixels = screenObject.getImageData(0,0,500,500);
function staticScreen()
{
requestAnimationFrame(currentAnimationFunction);
//Generate static
for(var i=0;i < pixels.data.length;i+=4)
{
pixels.data[i] = 255;
pixels.data[i + 1] = 255;
pixels.data[i + 2] = 255;
pixels.data[i + 3] = Math.floor((254-155)*Math.random()) + 156;
}
screenObject.putImageData(pixels,0,0,0,0,500,500);
//Draw 'No video input'
screenObject.fillStyle = "black";
screenObject.font = "30pt consolas";
screenObject.fillText("No video input",100,250,500);
}

Mine doesn't look identical to real TV static, but it's similar nonetheless. I'm just looping through all the pixels on canvas, and changing the RGB colour components of each pixel at a random coordinate to a random colour. The demo can be found over at CodePen.
The code is as follows:
// Setting up the canvas - size, setting a background, and getting the image data(all of the pixels) of the canvas.
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
canvas.width = 400;
canvas.height = 400;
canvasData = ctx.createImageData(canvas.width, canvas.height);
//Event listeners that set the canvas size to that of the window when the page loads, and each time the user resizes the window
window.addEventListener("load", windowResize);
window.addEventListener("resize", windowResize);
function windowResize(){
canvas.style.width = window.innerWidth + 'px';
canvas.style.height = window.innerHeight + 'px';
}
//A function that manipulates the array of pixel colour data created above using createImageData()
function setPixel(x, y, r, g, b, a){
var index = (x + y * canvasData.width) * 4;
canvasData.data[index] = r;
canvasData.data[index + 1] = g;
canvasData.data[index + 2] = b;
canvasData.data[index + 3] = a;
}
window.requestAnimationFrame(mainLoop);
function mainLoop(){
// Looping through all the colour data and changing each pixel to a random colour at a random coordinate, using the setPixel function defined earlier
for(i = 0; i < canvasData.data.length / 4; i++){
var red = Math.floor(Math.random()*256);
var green = Math.floor(Math.random()*256);
var blue = Math.floor(Math.random()*256);
var randX = Math.floor(Math.random()*canvas.width);
var randY = Math.floor(Math.random()*canvas.height);
setPixel(randX, randY, red, green, blue, 255);
}
//Place the image data we created and manipulated onto the canvas
ctx.putImageData(canvasData, 0, 0);
//And then do it all again...
window.requestAnimationFrame(mainLoop);
}

You can do it like this:
window.setInterval('generateNoise(.8)',50);
The 2nd arg 50 is a delay in milliseconds. Increasing 50 will slow it down and decreasing visa versa.
though.. this is going to severely affect web page performance. If it were me, I'd do the rendering server-side and render a handful of frame iterations and output as an animated gif. Not quite the same as infinite randomness, but would be a huge performance boost and IMO most people won't even notice.

Automatically Crop HTML5 canvas to contents

Let's say this is my canvas, with an evil-looking face drawn on it. I want to use toDataURL() to export my evil face as a PNG; however, the whole canvas is rasterised, including the 'whitespace' between the evil face and canvas edges.
+---------------+
| |
| |
| (.Y. ) |
| /_ |
| \____/ |
| |
| |
+---------------+
What is the best way to crop/trim/shrinkwrap my canvas to its contents, so my PNG is no larger than the face's 'bounding-box', like below? The best way seems to be scaling the canvas, but supposing the contents are dynamic...? I'm sure there should be a simple solution to this, but it's escaping me, with much Googling.
+------+
|(.Y. )|
| /_ |
|\____/|
+------+
Thanks!

Edited (see comments)
function cropImageFromCanvas(ctx) {
var canvas = ctx.canvas,
w = canvas.width, h = canvas.height,
pix = {x:[], y:[]},
imageData = ctx.getImageData(0,0,canvas.width,canvas.height),
x, y, index;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
index = (y * w + x) * 4;
if (imageData.data[index+3] > 0) {
pix.x.push(x);
pix.y.push(y);
}
}
}
pix.x.sort(function(a,b){return a-b});
pix.y.sort(function(a,b){return a-b});
var n = pix.x.length-1;
w = 1 + pix.x[n] - pix.x[0];
h = 1 + pix.y[n] - pix.y[0];
var cut = ctx.getImageData(pix.x[0], pix.y[0], w, h);
canvas.width = w;
canvas.height = h;
ctx.putImageData(cut, 0, 0);
var image = canvas.toDataURL();
}

If I understood well you want to "trim" away all the surronding your image / drawing, and adjust the canvas to that size (like if you do a "trim" command in Photoshop).
Here is how I'll do it.
Run thru all the canvas pixels checking if their alpha component is > 0 (that means that something is drawn in that pixel). Alternativelly you could check for the r,g,b values, if your canvas background is fullfilled with a solid color, for instance.
Get te coordinates of the top most left pixel non-empty, and same for the bottom most right one. So you'll get the coordinates of an imaginay "rectangle" containing the canvas area that is not empty.
Store that region of pixeldata.
Resize your canvas to its new dimensions (the ones of the region we got at step 2.)
Paste the saved region back to the canvas.
Et, voilá :)
Accesing pixeldata is quite slow depending on the size of your canvas (if its huge it can take a while). There are some optimizations around to work with raw canvas pixeldata (I think there is an article about this topic at MDN), I suggest you to google about it.
I prepared a small sketch in jsFiddle that you can use as starting point for your code.
Working sample at jsFiddle
Hope I've helped you.
c:.

Here's my take. I felt like all the other solutions were overly complicated. Though, after creating it, I now see it's the same solution as one other's, expect they just shared a fiddle and not a function.
function trimCanvas(canvas){
const context = canvas.getContext('2d');
const topLeft = {
x: canvas.width,
y: canvas.height,
update(x,y){
this.x = Math.min(this.x,x);
this.y = Math.min(this.y,y);
}
};
const bottomRight = {
x: 0,
y: 0,
update(x,y){
this.x = Math.max(this.x,x);
this.y = Math.max(this.y,y);
}
};
const imageData = context.getImageData(0,0,canvas.width,canvas.height);
for(let x = 0; x < canvas.width; x++){
for(let y = 0; y < canvas.height; y++){
const alpha = imageData.data[((y * (canvas.width * 4)) + (x * 4)) + 3];
if(alpha !== 0){
topLeft.update(x,y);
bottomRight.update(x,y);
}
}
}
const width = bottomRight.x - topLeft.x;
const height = bottomRight.y - topLeft.y;
const croppedCanvas = context.getImageData(topLeft.x,topLeft.y,width,height);
canvas.width = width;
canvas.height = height;
context.putImageData(croppedCanvas,0,0);
return canvas;
}

Here's code in ES syntax, short, fast and concise:
/**
* Trim a canvas.
*
* #author Arjan Haverkamp (arjan at avoid dot org)
* #param {canvas} canvas A canvas element to trim. This element will be trimmed (reference)
* #param {int} threshold Alpha threshold. Allows for trimming semi-opaque pixels too. Range: 0 - 255
* #returns {Object} Width and height of trimmed canvcas and left-top coordinate of trimmed area. Example: {width:400, height:300, x:65, y:104}
*/
const trimCanvas = (canvas, threshold = 0) => {
const ctx = canvas.getContext('2d'),
w = canvas.width, h = canvas.height,
imageData = ctx.getImageData(0, 0, w, h),
tlCorner = { x:w+1, y:h+1 },
brCorner = { x:-1, y:-1 };
for (let y = 0; y < h; y++) {
for (let x = 0; x < w; x++) {
if (imageData.data[((y * w + x) * 4) + 3] > threshold) {
tlCorner.x = Math.min(x, tlCorner.x);
tlCorner.y = Math.min(y, tlCorner.y);
brCorner.x = Math.max(x, brCorner.x);
brCorner.y = Math.max(y, brCorner.y);
}
}
}
const cut = ctx.getImageData(tlCorner.x, tlCorner.y, brCorner.x - tlCorner.x, brCorner.y - tlCorner.y);
canvas.width = brCorner.x - tlCorner.x;
canvas.height = brCorner.y - tlCorner.y;
ctx.putImageData(cut, 0, 0);
return {width:canvas.width, height:canvas.height, x:tlCorner.x, y:tlCorner.y};
}

The top voted answer here, as well as the implementations i found online trim one extra pixel which was very apparent when trying to trim text out of canvas. I wrote my own that worked better for me:
var img = new Image;
img.onload = () => {
var canvas = document.getElementById('canvas');
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
document.getElementById('button').addEventListener('click', ()=>{
autoCropCanvas(canvas, ctx);
document.getElementById('button').remove();
});
};
img.src = 'data:image/png;base64,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';
function autoCropCanvas(canvas, ctx) {
var bounds = {
left: 0,
right: canvas.width,
top: 0,
bottom: canvas.height
};
var rows = [];
var cols = [];
var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
for (var x = 0; x < canvas.width; x++) {
cols[x] = cols[x] || false;
for (var y = 0; y < canvas.height; y++) {
rows[y] = rows[y] || false;
const p = y * (canvas.width * 4) + x * 4;
const [r, g, b, a] = [imageData.data[p], imageData.data[p + 1], imageData.data[p + 2], imageData.data[p + 3]];
var isEmptyPixel = Math.max(r, g, b, a) === 0;
if (!isEmptyPixel) {
cols[x] = true;
rows[y] = true;
}
}
}
for (var i = 0; i < rows.length; i++) {
if (rows[i]) {
bounds.top = i ? i - 1 : i;
break;
}
}
for (var i = rows.length; i--; ) {
if (rows[i]) {
bounds.bottom = i < canvas.height ? i + 1 : i;
break;
}
}
for (var i = 0; i < cols.length; i++) {
if (cols[i]) {
bounds.left = i ? i - 1 : i;
break;
}
}
for (var i = cols.length; i--; ) {
if (cols[i]) {
bounds.right = i < canvas.width ? i + 1 : i;
break;
}
}
var newWidth = bounds.right - bounds.left;
var newHeight = bounds.bottom - bounds.top;
var cut = ctx.getImageData(bounds.left, bounds.top, newWidth, newHeight);
canvas.width = newWidth;
canvas.height = newHeight;
ctx.putImageData(cut, 0, 0);
}
<canvas id=canvas style='border: 1px solid pink'></canvas>
<button id=button>crop canvas</button>

How to scale an imageData in HTML canvas?

I have a canvas in my webpage; I create a new Image data in this canvas then I modify some pixel through myImgData.data[] array. Now I would like to scale this image and make it bigger. I tried by scaling the context but the image remains small. Is it possible to do this?
Thanks

You could draw the imageData to a new canvas, scale the original canvas and then draw the new canvas to the original canvas.
Something like this should work:
var imageData = context.getImageData(0, 0, 100, 100);
var newCanvas = $("<canvas>")
.attr("width", imageData.width)
.attr("height", imageData.height)[0];
newCanvas.getContext("2d").putImageData(imageData, 0, 0);
context.scale(1.5, 1.5);
context.drawImage(newCanvas, 0, 0);
Here's a functioning demo http://jsfiddle.net/Hm2xq/2/.

I needed to do it without the interpolation that putImageData() causes, so I did it by scaling the image data into a new, resized ImageData object. I can't think of any other time I've thought that using 5 nested for loops was a good idea:
function scaleImageData(imageData, scale) {
var scaled = c.createImageData(imageData.width * scale, imageData.height * scale);
for(var row = 0; row < imageData.height; row++) {
for(var col = 0; col < imageData.width; col++) {
var sourcePixel = [
imageData.data[(row * imageData.width + col) * 4 + 0],
imageData.data[(row * imageData.width + col) * 4 + 1],
imageData.data[(row * imageData.width + col) * 4 + 2],
imageData.data[(row * imageData.width + col) * 4 + 3]
];
for(var y = 0; y < scale; y++) {
var destRow = row * scale + y;
for(var x = 0; x < scale; x++) {
var destCol = col * scale + x;
for(var i = 0; i < 4; i++) {
scaled.data[(destRow * scaled.width + destCol) * 4 + i] =
sourcePixel[i];
}
}
}
}
}
return scaled;
}
I hope that at least one other programmer can copy and paste this into their editor while muttering, "There but for the grace of god go I."

I know it's an old subject, but since people like may find it useful, I add my optimization to the code of rodarmor :
function scaleImageData(imageData, scale) {
var scaled = ctx.createImageData(imageData.width * scale, imageData.height * scale);
var subLine = ctx.createImageData(scale, 1).data
for (var row = 0; row < imageData.height; row++) {
for (var col = 0; col < imageData.width; col++) {
var sourcePixel = imageData.data.subarray(
(row * imageData.width + col) * 4,
(row * imageData.width + col) * 4 + 4
);
for (var x = 0; x < scale; x++) subLine.set(sourcePixel, x*4)
for (var y = 0; y < scale; y++) {
var destRow = row * scale + y;
var destCol = col * scale;
scaled.data.set(subLine, (destRow * scaled.width + destCol) * 4)
}
}
}
return scaled;
}
This code uses less loops and runs roughly 30 times faster. For instance, on a 100x zoom of a 100*100 area this codes takes 250 ms while the other takes more than 8 seconds.

You can scale the canvas using the drawImage method.
context = canvas.getContext('2d');
context.drawImage( canvas, 0, 0, 2*canvas.width, 2*canvas.height );
This would scale the image to double the size and render the north-west part of it to the canvas. Scaling is achieved with the third and fourth parameters to the drawImage method, which specify the resulting width and height of the image.
See docs at MDN https://developer.mozilla.org/en-US/docs/DOM/CanvasRenderingContext2D#drawImage%28%29

#Castrohenge's answer works, but as Muhammad Umer points out, it messes up the mouse coordinates on the original canvas after that. If you want to maintain the ability to perform additional scales (for cropping, etc.) then you need to utilize a second canvas (for scaling) and then fetch the image data from the second canvas and put that into the original canvas. Like so:
function scaleImageData(imageData, scale){
var newCanvas = $("<canvas>")
.attr("width", imageData.width)
.attr("height", imageData.height)[0];
newCanvas.getContext("2d").putImageData(imageData, 0, 0);
// Second canvas, for scaling
var scaleCanvas = $("<canvas>")
.attr("width", canvas.width)
.attr("height", canvas.height)[0];
var scaleCtx = scaleCanvas.getContext("2d");
scaleCtx.scale(scale, scale);
scaleCtx.drawImage(newCanvas, 0, 0);
var scaledImageData = scaleCtx.getImageData(0, 0, scaleCanvas.width, scaleCanvas.height);
return scaledImageData;
}

Nowadays, the best way to render a scaled ImageData object is generally to create an ImageBitmap from it.
All modern browsers finally do support it.
This will use a faster path to render the ImageData's content to a bitmap readily available to be painted by drawImage(), theoretically a lot faster than the second best option of putting the ImageData on a secondary <canvas> and redraw that <canvas>.
The main catch-up is that createImageBitmap() is asynchronous*, and thus it may not fit in an animation frame very well.
(async () => {
// here I'll just make some noise in my ImageData
const imagedata = new ImageData(100, 100);
const arr = new Uint32Array(imagedata.data.buffer);
for( let i = 0; i < arr.length; i++ ) {
arr[i] = Math.random() * 0xFFFFFF + 0xFF000000;
}
// now to render it bigger
const bitmap = await createImageBitmap(imagedata);
const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
ctx.imageSmoothingEnabled = false; // keep pixel perfect
ctx.drawImage(bitmap, 0, 0, canvas.width, canvas.height);
})();
<canvas width="1000" height="1000"></canvas>
* Technically, only Firefox does implement createImageBitmap(<ImageData>) asynchronously, Chrome and Safari will resolve the returned Promise synchronously, and there, it's safe to use it in an animation frame: https://jsfiddle.net/vraz3xcg/