I'm really struggling with a couple problems in the HTML5 canvas.
I've posted the project to GitHub pages (https://swedy13.github.io/) and added an image (the circles are in motion) so you can see the issue. Basically, if you scroll down you'll find several green circles bouncing around on the page. I'd like to replace those with my client logos.
I'm calling requestAnimation from three files based on different actions, all of which can be found in https://github.com/swedy13/swedy13.github.io/tree/master/assets/js
Filenames:
- filters.js (calls requestAnimation when you use the filters)
- main.js (on load and resize)
- portfolio.js (this is where the canvas code is)
Update: I've added the "portfolio.js" code below so the answer can be self-contained.
function runAnimation(width, height, type){
var canvas = document.getElementsByTagName('canvas')[0];
var c = canvas.getContext('2d');
// ---- DIMENSIONS ---- //
// Container
var x = width;
var y = height - 65;
canvas.width = x;
canvas.height = y;
var container = {x: 0 ,y: 0 ,width: x, height: y};
// Portrait Variables
var cPos = 200;
var cMargin = 70;
var cSpeed = 3;
var r = x*.075;
if (y > x && x >= 500) {
cPos = x * (x / y) - 150;
cMargin = 150;
}
// Landscape Variables
if (x > y) {
cPos = y * (y / x) - 50;
cMargin = 150;
cSpeed = 3;
r = x*.05;
}
// ---- CIRCLES ---- //
// Circles
var circles = [];
var img = new Image();
// Gets active post ids and count
var activeName = [];
var activeLogo = [];
var activePosts = $('.active').map(function() {
activeName.push($(this).text().replace(/\s+/g, '-').toLowerCase());
// Returns the image source
/*activeLogo.push($(this).find('img').prop('src'));*/
// Returns an image node
var elem = document.getElementsByClassName($(this).text().replace(/\s+/g, '-').toLowerCase())
activeLogo.push(elem[0].childNodes[0]);
});
// Populates circle data
for (var i = 0; i < $('.active').length; i++) {
circles.push({
id:activeName[i],
r:r,
color: 100,
/*image: activeLogo[i],*/
x:Math.random() * cPos + cMargin,
y:Math.random() * cPos + cMargin,
vx:Math.random() * cSpeed + .25,
vy:Math.random() * cSpeed + .25
});
}
// ---- DRAW ---- //
requestAnimationFrame(draw);
function draw(){
c.fillStyle = 'white';
c.fillRect(container.x, container.y, container.width, container.height);
for (var i = 0; i < circles.length; i++){
/*var img = new Image();
var path = circles[i].image;*/
/*var size = circles[i].r * 2;*/
/*img.src = circles[4].image;*/
var img = activeLogo[i];
img.onload = function (circles) {
/*c.drawImage(img, 0, 0, size, size);*/
var pattern = c.createPattern(this, "repeat");
c.fillStyle = pattern;
c.fill();
};
c.fillStyle = 'hsl(' + circles[i].color + ', 100%, 50%)';
c.beginPath();
c.arc(circles[i].x, circles[i].y, circles[i].r, 0, 2*Math.PI, false);
c.fill();
// If the circle size/position is greater than the canvas width, bounce x
if ((circles[i].x + circles[i].vx + circles[i].r > container.width) || (circles[i].x - circles[i].r + circles[i].vx < container.x)) {
circles[i].vx = -circles[i].vx;
}
// If the circle size/position is greater than the canvas width, bounce y
if ((circles[i].y + circles[i].vy + circles[i].r > container.height) || (circles[i].y - circles[i].r + circles[i].vy < container.y)){
circles[i].vy = -circles[i].vy;
}
// Generates circle motion by adding position and velocity each frame
circles[i].x += circles[i].vx;
circles[i].y += circles[i].vy;
}
requestAnimationFrame(draw);
}
}
The way it works right now is:
1. I have my portfolio content set to "display: none" (eventually it will be a pop-up when they click on one of the circles).
2. The canvas is getting the portfolio objects from the DOM, including the image that I can't get to work.
3. If I use the "onload()" function, I can get the images to show up and repeat in the background. But it's just a static background - the circles are moving above it and revealing the background. That isn't what I want.
So basically, I'm trying to figure out how to attach the background image to the circle (based on the circle ID).
----------------- UPDATE -----------------
I can now clip the image to a circle and get the circle to move in the background. But it isn't visible on the page (I can tell it's moving by console logging it's position). The only time I see anything is when the circle lines up with the images position, then it shows.
function runAnimation(width, height, type){
var canvas = document.getElementsByTagName('canvas')[0];
var c = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
// Collects portfolio information from the DOM
var activeName = [];
var activeLogo = [];
$('.active').map(function() {
var text = $(this).text().replace(/\s+/g, '-').toLowerCase();
var elem = document.getElementsByClassName(text);
activeName.push(text);
activeLogo.push(elem[0].childNodes[0]);
});
var img = new Image();
img.onload = start;
var circles = [];
var cPos = 200;
var cMargin = 70;
var cSpeed = 3;
for (var i = 0; i < 1; i++) {
circles.push({
id: activeName[i],
img: activeLogo[i],
size: 50,
xPos: Math.random() * cPos + cMargin,
yPos: Math.random() * cPos + cMargin,
xVel: Math.random() * cSpeed + .25,
yVel: Math.random() * cSpeed + .25,
});
img.src = circles[i].img;
}
requestAnimationFrame(start);
function start(){
for (var i = 0; i < circles.length; i++) {
var circle = createImageInCircle(circles[i].img, circles[i].size, circles[i].xPos, circles[i].yPos);
c.drawImage(circle, circles[i].size, circles[i].size);
animateCircle(circles[i]);
}
requestAnimationFrame(start);
}
function createImageInCircle(img, radius, x, y){
var canvas2 = document.createElement('canvas');
var c2 = canvas2.getContext('2d');
canvas2.width = canvas2.height = radius*2;
c2.fillStyle = 'white';
c2.beginPath();
c2.arc(x, y, radius, 0, Math.PI*2);
c2.fill();
c2.globalCompositeOperation = 'source-atop';
c2.drawImage(img, 0, 0, 100, 100);
return(canvas2);
}
function animateCircle(circle) {
// If the circle size/position is greater than the canvas width, bounce x
if ((circle.xPos + circle.xVel + circle.size > canvas.width) || (circle.xPos - circle.size + circle.xVel < 0)) {
console.log('Bounce X');
circle.xVel = -circle.xVel;
}
// If the circle size/position is greater than the canvas width, bounce y
if ((circle.yPos + circle.yVel + circle.size > canvas.height) || (circle.yPos + circle.yVel - circle.size < 0)) {
console.log('Bounce Y');
circle.yVel = -circle.yVel;
}
// Generates circle motion by adding position and velocity each frame
circle.xPos += circle.xVel;
circle.yPos += circle.yVel;
}
}
I'm not sure if I'm animating the correct thing. I've tried animating canvas2, but that didn't make sense to me.
PS - Sorry for the GitHub formatting, not sure why it looks like that.
PPS - Apologies for any junk code I didn't clean up. I've tried a lot of stuff and probably lost track of some of the changes.
PPPS - And forgive me for not making the answer self-contained. I thought linking to GitHub would be more useful, but I've updated the question to contain all the necessary info. Thanks for the feedback.
To get you started...
Here's how to clip an image into a circle using compositing.
The example code creates a single canvas logo-ball that you can reuse for each of your bouncing balls.
var logoball1=dreateImageInCircle(logoImg1,50);
var logoball2=dreateImageInCircle(logoImg2,50);
Then you can draw each logo-ball onto your main canvas like this:
ctx.drawImage(logoball1,35,40);
ctx.drawImage(logoball2,100,75);
There are many examples here on Stackoverflow of how to animate the balls around the canvas so I leave that part to you.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/m%26m600x455.jpg";
function start(){
var copy=createImageInCircle(img,50);
ctx.drawImage(copy,20,75);
ctx.drawImage(copy,150,120);
ctx.drawImage(copy,280,75);
}
function createImageInCircle(img,radius){
var c=document.createElement('canvas');
var cctx=c.getContext('2d');
c.width=c.height=radius*2;
cctx.beginPath();
cctx.arc(radius,radius,radius,0,Math.PI*2);
cctx.fill();
cctx.globalCompositeOperation='source-atop';
cctx.drawImage(img,radius-img.width/2,radius-img.height/2);
return(c);
}
body{ background-color:white; }
#canvas{border:1px solid red; }
<canvas id="canvas" width=512 height=512></canvas>
I have an image drawn to an html cavas. I would like to be able to rotate the image by 90 degrees but I can't seem to find an example on how to rotate the entire canvas image, only an object on the canvas.
Does anyone have example code to rotate an entire canvas by 90 degrees?
I accepted an anwser below but wanted to provide additional example code : http://jsfiddle.net/VTyNF/1/
<canvas id="myCanvas" width="578" height="200"></canvas>
<script>
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
context.translate(canvas.width/2,canvas.height/2)
context.rotate(90 * (Math.PI / 180));
context.beginPath();
context.rect(188 - canvas.width/2, 50 - canvas.height/2, 200, 100);
context.fillStyle = 'yellow';
context.fill();
context.lineWidth = 7;
context.strokeStyle = 'black';
context.stroke();
</script>
You would have to apply this rotation before you draw your canvas. You can't rotate anything that is already drawn.
So:
To rotate a canvas, the content.rotate() expects a value in radians. So first, lets make it simple by converting degrees to radians using:
function getRadianAngle(degreeValue) {
return degreeValue * Math.PI / 180;
}
You may want to translate the canvas first before rotating so that it's origin is set correctly.
context.translate(context.width/2,context.height/2);
Once we know what value we want, we simply rotate the canvas before we draw anything!
Please note, in your example, the rectangle you have drawn, is also being offset in the first two parameters of context.rect(X,Y,W,H)`.
I find it's easier to set widths as variables, then do simple math to re position the box automatically, notice now it sits perfectly in the center, and rotates nicely!
DEMO: http://jsfiddle.net/shannonhochkins/VTyNF/6/
Say your canvas element has id "foo". In JavaScript you could do something like this:
var canvas = document.getElementById('foo'),
context = canvas.getContext('2d');
// Rotates the canvas 90 degrees
context.rotate(90 * (Math.PI / 180));
Could you use CSS to rotate the <canvas> element with transform: rotate(90deg);?
You can easily rotate the image ninety degrees by manipulating the pixel data. If your canvas isn't square, you will have to make some choices about what the 'correct' answer will be.
Use the getImageData function to retrieve the pixels, manipulate them in the usual manner, and use putImageData to display the result.
This version doesn't require center point for 90 degree turn:
(Not as easy becase it's a 1d array with 4 values per pixel, initialDimensions means horizontal or 0, 180 rotation state vs 90, 270)
//...
const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d', {willReadFrequently: true});
const img = document.createElement('img');
const file = inp.files[0]; // file from user input
img.src = URL.createObjectURL(file);
img.initialDimensions = true;
img.addEventListener('load', function () {
canvas.width = this.width;
canvas.height = this.height;
canvas.crossOrigin = "anonymous";
context.drawImage(img, 0, 0);
rotateClockwiseBy90(canvas, context, img);
}
}
function rotateClockwiseBy90(canvas, context, img) {
if (img.initialDimensions == undefined) {
img.initialDimensions = true;
}
var width, height;
if (img.initialDimensions) {
width = img.naturalWidth;
height = img.naturalHeight;
img.initialDimensions = false;
}
else {
width = img.naturalHeight;
height = img.naturalWidth;
img.initialDimensions = true;
}
const imageData = context.getImageData(0, 0, width, height);
const rotatedImageData = context.createImageData(height, width);
//[redIndex, greenIndex, blueIndex, alphaIndex]
const width4 = width * 4;
const height4 = height * 4;
for (let y = 0; y < height4; y += 4) {
for (let x = 0; x < width4; x += 4) {
rotatedImageData.data[x * height + (height4 - y -1) - 3] = imageData.data[y * width + x];
rotatedImageData.data[x * height + (height4 - y -1) - 2] = imageData.data[y * width + x + 1];
rotatedImageData.data[x * height + (height4 - y -1) - 1] = imageData.data[y * width + x + 2];
rotatedImageData.data[x * height + (height4 - y -1)] = imageData.data[y * width + x + 3];
}
}
const cw = canvas.width;
canvas.width = canvas.height;
canvas.height = cw;
context.putImageData(rotatedImageData, 0, 0);
}
If someone is trying to understand the logic:
rotatedImageData.data[x * height ...
should really be:
rotatedImageData.data[x / 4 * height * 4 ...
because for the rotated array x represents row number and height represents row length, but the result is same.
Version for counterclockwise rotation:
for (let y = 0; y < height4; y += 4) {
for (let x = 0; x < width4; x += 4) {
rotatedImageData.data[(height4 * (width - x/4) - height4 + y)] = imageData.data[y * width + x];
rotatedImageData.data[(height4 * (width - x/4) - height4 + y) + 1] = imageData.data[y * width + x + 1];
rotatedImageData.data[(height4 * (width - x/4) - height4 + y) + 2] = imageData.data[y * width + x + 2];
rotatedImageData.data[(height4 * (width - x/4) - height4 + y) + 3] = imageData.data[y * width + x + 3];
}
}
So let me start off by saying I am trying to create a large image or room, say 5000 by 3750, and have the canvas or viewing area only 800 by 599, always following the player piece. I did find a good guide on how to do this, using a background and Player drawn in java script (not taken from a sprite sheet). But what I have is a sprite sheet with the background, and the player, I have gotten the player to work on the background drawn from JavaScript, but not taken from the sprite sheet like I want to do.
Here is some of the code:
// wrapper for "class" Map
(function(){
function Map(width, height){
// map dimensions
this.width = width;
this.height = height;
// map texture
this.image = null;
}
// generate an example of a large map
Map.prototype.generate = function(){
ctxBg.drawImage(imgSprite,0,2250,5000,3750,0,0,5000,3750);
}
// draw the map adjusted to camera
Map.prototype.draw = function(context, xView, yView){
var sx, sy, dx, dy;
var sWidth, sHeight, dWidth, dHeight;
// offset point to crop the image
sx = xView;
sy = yView;
// dimensions of cropped image
sWidth = 800;
sHeight = 599;
// if cropped image is smaller than canvas we need to change the source dimensions
if(800 - sx < sWidth){
sWidth = 800 - sx;
}
if(599 - sy < sHeight){
sHeight = 599 - sy;
}
// location on canvas to draw the croped image
dx = 0;
dy = 0;
// match destination with source to not scale the image
dWidth = sWidth;
dHeight = sHeight;
context.drawImage(imgSprite, sx, sy, sWidth, sHeight, dx, dy, dWidth, dHeight);
}
// add "class" Map to our Game object
Game.Map = Map;
})();
// Game Script
(function(){
// prepaire our game canvas
var canvas = document.getElementById("gameCanvas");
var context = canvas.getContext("2d");
// game settings:
var FPS = 30;
var INTERVAL = 1000/FPS; // milliseconds
var STEP = INTERVAL/1000 // seconds
// setup an object that represents the room
var room = {
width: 5000,
height: 3750,
map: new Game.Map(5000, 3750)
};
room.map.generate();
heres the camra/player codes:
(function(){
function Rectangle(left, top, width, height){
this.left = left || 0;
this.top = top || 0;
this.right = (left + width) || 0;
this.bottom = (top + height) || 0;
}
Rectangle.prototype.set = function(left, top, /*optional*/width, /*optional*/height){
this.left = left;
this.top = top;
this.width = width || this.width;
this.height = height || this.height;
this.right = (this.left + this.width);
this.bottom = (this.top + this.height);
}
Rectangle.prototype.within = function(r) {
return (r.left <= this.left &&
r.right >= this.right &&
r.top <= this.top &&
r.bottom >= this.bottom);
}
Rectangle.prototype.overlaps = function(r) {
return (this.left < r.right &&
r.left < this.right &&
this.top < r.bottom &&
r.top < this.bottom);
}
// add "class" Rectangle to our Game object
Game.Rectangle = Rectangle;
})();
// wrapper for "class" Camera (avoid global objects)
(function(){
// possibles axis to move the camera
var AXIS = {
NONE: "none",
HORIZONTAL: "horizontal",
VERTICAL: "vertical",
BOTH: "both"
};
// Camera constructor
function Camera(xView, yView, canvasWidth, canvasHeight, worldWidth, worldHeight)
{
// position of camera (left-top coordinate)
this.xView = xView || 0;
this.yView = yView || 0;
// distance from followed object to border before camera starts move
this.xDeadZone = 0; // min distance to horizontal borders
this.yDeadZone = 0; // min distance to vertical borders
// viewport dimensions
this.wView = 800;
this.hView = 599;
// allow camera to move in vertical and horizontal axis
this.axis = AXIS.BOTH;
// object that should be followed
this.followed = null;
// rectangle that represents the viewport
this.viewportRect = new Game.Rectangle(this.xView, this.yView, this.wView, this.hView);
// rectangle that represents the world's boundary (room's boundary)
this.worldRect = new Game.Rectangle(this.xView, this.yView, this.wView, this.hView);
}
// gameObject needs to have "x" and "y" properties (as world(or room) position)
Camera.prototype.follow = function(gameObject, xDeadZone, yDeadZone)
{
this.followed = gameObject;
this.xDeadZone = xDeadZone;
this.yDeadZone = yDeadZone;
}
Camera.prototype.update = function()
{
// keep following the player (or other desired object)
if(this.followed != null)
{
if(this.axis == AXIS.HORIZONTAL || this.axis == AXIS.BOTH)
{
// moves camera on horizontal axis based on followed object position
if(this.followed.x - this.xView + this.xDeadZone > this.wView)
this.xView = this.followed.x - (this.wView - this.xDeadZone);
else if(this.followed.x - this.xDeadZone < this.xView)
this.xView = this.followed.x - this.xDeadZone;
}
if(this.axis == AXIS.VERTICAL || this.axis == AXIS.BOTH)
{
// moves camera on vertical axis based on followed object position
if(this.followed.y - this.yView + this.yDeadZone > this.hView)
this.yView = this.followed.y - (this.hView - this.yDeadZone);
else if(this.followed.y - this.yDeadZone < this.yView)
this.yView = this.followed.y - this.yDeadZone;
}
}
// update viewportRect
this.viewportRect.set(this.xView, this.yView);
// don't let camera leaves the world's boundary
if(!this.viewportRect.within(this.worldRect))
{
if(this.viewportRect.left < this.worldRect.left)
this.xView = this.worldRect.left;
if(this.viewportRect.top < this.worldRect.top)
this.yView = this.worldRect.top;
if(this.viewportRect.right > this.worldRect.right)
this.xView = this.worldRect.right - this.wView;
if(this.viewportRect.bottom > this.worldRect.bottom)
this.yView = this.worldRect.bottom - this.hView;
}
}
// add "class" Camera to our Game object
Game.Camera = Camera;
})();
// wrapper for "class" Player
(function(){
function Player(x, y){
// (x, y) = center of object
// ATTENTION:
// it represents the player position on the world(room), not the canvas position
this.x = x;
this.y = y;
this.srcX = 1700;
this.srcY = 599;
this.drawX = 350;
this.drawY = 400;
xView = this.x-this.width/2;
yView = this.y-this.height/2;
// move speed in pixels per second
this.speed = 100;
// render properties
this.width = 85;
this.height = 80;
}
Player.prototype.update = function(step, worldWidth, worldHeight){
// parameter step is the time between frames ( in seconds )
// check controls and move the player accordingly
if(Game.controls.left)
this.x -= this.speed * step;
if(Game.controls.up)
this.y -= this.speed * step;
if(Game.controls.right)
this.x += this.speed * step;
if(Game.controls.down)
this.y += this.speed * step;
// don't let player leaves the world's boundary
if(this.x - this.width/2 < 0){
this.x = this.width/2;
}
if(this.y - this.height/2 < 0){
this.y = this.height/2;
}
if(this.x + this.width/2 > worldWidth){
this.x = worldWidth - this.width/2;
}
if(this.y + this.height/2 > worldHeight){
this.y = worldHeight - this.height/2;
}
}
Player.prototype.draw = function(/*context,*/ xView, yView){
ctxPlayer.clearRect(0,0,800,599);
context.save();
ctxPlayer.drawImage(imgSprite,this.srcX,this.srcY,this.width,this.height,(this.x-this.width/2),(this.y-this.height/2),this.width,this.height);
context.restore();
}
// add "class" Player to our Game object
Game.Player = Player;
})();
It shows the image and player, but the canvas doesn't follow the player object, It does if I use a background like this, though:
(function(){
function Map(width, height){
this.width = width;
this.height = height;
this.image = null;
}
Map.prototype.generate = function(){
var ctx = document.createElement("canvas").getContext("2d");
ctx.canvas.width = this.width;
ctx.canvas.height = this.height;
var rows = ~~(this.width/44) + 1;
var columns = ~~(this.height/44) + 1;
var color = "red";
ctx.save();
ctx.fillStyle = "red";
for (var x = 0, i = 0; i < rows; x+=44, i++) {
ctx.beginPath();
for (var y = 0, j=0; j < columns; y+=44, j++) {
ctx.rect (x, y, 40, 40);
}
color = (color == "red" ? "blue" : "red");
ctx.fillStyle = color;
ctx.fill();
ctx.closePath();
}
ctx.restore();
this.image = new Image();
this.image.src = ctx.canvas.toDataURL("image/png");
// clear context
ctx = null;
}
// draw the map adjusted to camera
Map.prototype.draw = function(context, xView, yView){
var sx, sy, dx, dy;
var sWidth, sHeight, dWidth, dHeight;
// offset point to crop the image
sx = xView;
sy = yView;
// dimensions of cropped image
sWidth = context.canvas.width;
sHeight = context.canvas.height;
// if cropped image is smaller than canvas we need to change the source dimensions
if(this.image.width - sx < sWidth){
sWidth = this.image.width - sx;
}
if(this.image.height - sy < sHeight){
sHeight = this.image.height - sy;
}
dx = 0;
dy = 0;
dWidth = sWidth;
dHeight = sHeight;
context.drawImage(this.image, sx, sy, sWidth, sHeight, dx, dy, dWidth, dHeight);
}
Game.Map = Map;
})();
I looked around, did some google searches and used a JavaScript checker, but no luck. Any suggestions/advice is much appreciated.
I'll give it a shot anyways. So, for the theoretical part:
What you are trying to achieve is simple Scene Management. A Scene needs a Camera, an object that stores the X and Y offset and the Width and Height it is going to display (The Width and Height is also known as the Projection Plane in 3D graphics). In every frame you will draw your Scene (or World) by the offset of your Camera.
To the implementation:
To draw a large image onto a small Canvas, just use the drawImage() function with all 9 parameters as you allready do.
To draw many small images like Tiles, i recommend taking a look at Scene graphs, i wrote a more in-depth answer some time ago at Collision detection in HTML5 canvas. Optimization too
If you draw many Objects per frame, note that you can always create canvas objects that are not in the html DOM to cache draw results, it is necessary for good performance. A draw call is expensive because of its render state changes and streaming costs, not because of the pixels itself.
Finally, to draw your character on top, you would need some sort of z index, so your draw loop knows the player is on top of the ground, you can do this via layers or storing a z index for your game objects.
So far, you're already on the right track!
I'm trying to create a thumbnail image on the client side using javascript and a canvas element, but when I shrink the image down, it looks terrible. It looks as if it was downsized in photoshop with the resampling set to 'Nearest Neighbor' instead of Bicubic. I know its possible to get this to look right, because this site can do it just fine using a canvas as well. I've tried using the same code they do as shown in the "[Source]" link, but it still looks terrible. Is there something I'm missing, some setting that needs to be set or something?
EDIT:
I'm trying to resize a jpg. I have tried resizing the same jpg on the linked site and in photoshop, and it looks fine when downsized.
Here is the relevant code:
reader.onloadend = function(e)
{
var img = new Image();
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
};
img.src = reader.result;
}
EDIT2:
Seems I was mistaken, the linked website wasn't doing any better of a job of downsizing the image. I tried the other methods suggested and none of them look any better. This is what the different methods resulted in:
Photoshop:
Canvas:
Image with image-rendering: optimizeQuality set and scaled with width/height:
Image with image-rendering: optimizeQuality set and scaled with -moz-transform:
Canvas resize on pixastic:
I guess this means firefox isn't using bicubic sampling like its supposed to. I'll just have to wait until they actually add it.
EDIT3:
Original Image
So what do you do if all the browsers (actually, Chrome 5 gave me quite good one) won't give you good enough resampling quality? You implement them yourself then! Oh come on, we're entering the new age of Web 3.0, HTML5 compliant browsers, super optimized JIT javascript compilers, multi-core(†) machines, with tons of memory, what are you afraid of? Hey, there's the word java in javascript, so that should guarantee the performance, right? Behold, the thumbnail generating code:
// returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function(x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1;
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
};
}
// elem: canvas element, img: image element, sx: scaled width, lobes: kernel radius
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width : sx,
height : Math.round(img.height * sx / img.width),
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(this.process1, 0, this, 0);
}
thumbnailer.prototype.process1 = function(self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2)
+ Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(self.process1, 0, self, u);
else
setTimeout(self.process2, 0, self);
};
thumbnailer.prototype.process2 = function(self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0, self.dest.width, self.dest.height);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
};
...with which you can produce results like these!
so anyway, here is a 'fixed' version of your example:
img.onload = function() {
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 188, 3); //this produces lanczos3
// but feel free to raise it up to 8. Your client will appreciate
// that the program makes full use of his machine.
document.body.appendChild(canvas);
};
Now it's time to pit your best browsers out there and see which one will least likely increase your client's blood pressure!
Umm, where's my sarcasm tag?
(since many parts of the code is based on Anrieff Gallery Generator is it also covered under GPL2? I don't know)
† actually due to limitation of javascript, multi-core is not supported.
Fast image resize/resample algorithm using Hermite filter with JavaScript. Support transparency, gives good quality. Preview:
Update: version 2.0 added on GitHub (faster, web workers + transferable objects). Finally i got it working!
Git: https://github.com/viliusle/Hermite-resize
Demo: http://viliusle.github.io/miniPaint/
/**
* Hermite resize - fast image resize/resample using Hermite filter. 1 cpu version!
*
* #param {HtmlElement} canvas
* #param {int} width
* #param {int} height
* #param {boolean} resize_canvas if true, canvas will be resized. Optional.
*/
function resample_single(canvas, width, height, resize_canvas) {
var width_source = canvas.width;
var height_source = canvas.height;
width = Math.round(width);
height = Math.round(height);
var ratio_w = width_source / width;
var ratio_h = height_source / height;
var ratio_w_half = Math.ceil(ratio_w / 2);
var ratio_h_half = Math.ceil(ratio_h / 2);
var ctx = canvas.getContext("2d");
var img = ctx.getImageData(0, 0, width_source, height_source);
var img2 = ctx.createImageData(width, height);
var data = img.data;
var data2 = img2.data;
for (var j = 0; j < height; j++) {
for (var i = 0; i < width; i++) {
var x2 = (i + j * width) * 4;
var weight = 0;
var weights = 0;
var weights_alpha = 0;
var gx_r = 0;
var gx_g = 0;
var gx_b = 0;
var gx_a = 0;
var center_y = (j + 0.5) * ratio_h;
var yy_start = Math.floor(j * ratio_h);
var yy_stop = Math.ceil((j + 1) * ratio_h);
for (var yy = yy_start; yy < yy_stop; yy++) {
var dy = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
var center_x = (i + 0.5) * ratio_w;
var w0 = dy * dy; //pre-calc part of w
var xx_start = Math.floor(i * ratio_w);
var xx_stop = Math.ceil((i + 1) * ratio_w);
for (var xx = xx_start; xx < xx_stop; xx++) {
var dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
var w = Math.sqrt(w0 + dx * dx);
if (w >= 1) {
//pixel too far
continue;
}
//hermite filter
weight = 2 * w * w * w - 3 * w * w + 1;
var pos_x = 4 * (xx + yy * width_source);
//alpha
gx_a += weight * data[pos_x + 3];
weights_alpha += weight;
//colors
if (data[pos_x + 3] < 255)
weight = weight * data[pos_x + 3] / 250;
gx_r += weight * data[pos_x];
gx_g += weight * data[pos_x + 1];
gx_b += weight * data[pos_x + 2];
weights += weight;
}
}
data2[x2] = gx_r / weights;
data2[x2 + 1] = gx_g / weights;
data2[x2 + 2] = gx_b / weights;
data2[x2 + 3] = gx_a / weights_alpha;
}
}
//clear and resize canvas
if (resize_canvas === true) {
canvas.width = width;
canvas.height = height;
} else {
ctx.clearRect(0, 0, width_source, height_source);
}
//draw
ctx.putImageData(img2, 0, 0);
}
Try pica - that's a highly optimized resizer with selectable algorythms. See demo.
For example, original image from first post is resized in 120ms with Lanczos filter and 3px window or 60ms with Box filter and 0.5px window. For huge 17mb image 5000x3000px resize takes ~1s on desktop and 3s on mobile.
All resize principles were described very well in this thread, and pica does not add rocket science. But it's optimized very well for modern JIT-s, and is ready to use out of box (via npm or bower). Also, it use webworkers when available to avoid interface freezes.
I also plan to add unsharp mask support soon, because it's very useful after downscale.
I know this is an old thread but it might be useful for some people such as myself that months after are hitting this issue for the first time.
Here is some code that resizes the image every time you reload the image. I am aware this is not optimal at all, but I provide it as a proof of concept.
Also, sorry for using jQuery for simple selectors but I just feel too comfortable with the syntax.
$(document).on('ready', createImage);
$(window).on('resize', createImage);
var createImage = function(){
var canvas = document.getElementById('myCanvas');
canvas.width = window.innerWidth || $(window).width();
canvas.height = window.innerHeight || $(window).height();
var ctx = canvas.getContext('2d');
img = new Image();
img.addEventListener('load', function () {
ctx.drawImage(this, 0, 0, w, h);
});
img.src = 'http://www.ruinvalor.com/Telanor/images/original.jpg';
};
html, body{
height: 100%;
width: 100%;
margin: 0;
padding: 0;
background: #000;
}
canvas{
position: absolute;
left: 0;
top: 0;
z-index: 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<html>
<head>
<meta charset="utf-8" />
<title>Canvas Resize</title>
</head>
<body>
<canvas id="myCanvas"></canvas>
</body>
</html>
My createImage function is called once when the document is loaded and after that it is called every time the window receives a resize event.
I tested it in Chrome 6 and Firefox 3.6, both on the Mac. This "technique" eats processor as it if was ice cream in the summer, but it does the trick.
I've put up some algorithms to do image interpolation on html canvas pixel arrays that might be useful here:
https://web.archive.org/web/20170104190425/http://jsperf.com:80/pixel-interpolation/2
These can be copy/pasted and can be used inside of web workers to resize images (or any other operation that requires interpolation - I'm using them to defish images at the moment).
I haven't added the lanczos stuff above, so feel free to add that as a comparison if you'd like.
This is a javascript function adapted from #Telanor's code. When passing a image base64 as first argument to the function, it returns the base64 of the resized image. maxWidth and maxHeight are optional.
function thumbnail(base64, maxWidth, maxHeight) {
// Max size for thumbnail
if(typeof(maxWidth) === 'undefined') var maxWidth = 500;
if(typeof(maxHeight) === 'undefined') var maxHeight = 500;
// Create and initialize two canvas
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
// Create original image
var img = new Image();
img.src = base64;
// Determine new ratio based on max size
var ratio = 1;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
// Draw original image in second canvas
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
// Copy and resize second canvas to first canvas
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
return canvas.toDataURL();
}
I'd highly suggest you check out this link and make sure it is set to true.
Controlling image scaling behavior
Introduced in Gecko 1.9.2 (Firefox 3.6
/ Thunderbird 3.1 / Fennec 1.0)
Gecko 1.9.2 introduced the
mozImageSmoothingEnabled property to
the canvas element; if this Boolean
value is false, images won't be
smoothed when scaled. This property is
true by default. view plainprint?
cx.mozImageSmoothingEnabled = false;
If you're simply trying to resize an image, I'd recommend setting width and height of the image with CSS. Here's a quick example:
.small-image {
width: 100px;
height: 100px;
}
Note that the height and width can also be set using JavaScript. Here's quick code sample:
var img = document.getElement("my-image");
img.style.width = 100 + "px"; // Make sure you add the "px" to the end,
img.style.height = 100 + "px"; // otherwise you'll confuse IE
Also, to ensure that the resized image looks good, add the following css rules to image selector:
-ms-interpolation-mode: bicubic: introduce in IE7
image-rendering: optimizeQuality: introduced in FireFox 3.6
As far as I can tell, all browsers except IE using an bicubic algorithm to resize images by default, so your resized images should look good in Firefox and Chrome.
If setting the css width and height doesn't work, you may want to play with a css transform:
-moz-transform: scale(sx[, sy])
-webkit-transform:scale(sx[, sy])
If for whatever reason you need to use a canvas, please note that there are two ways an image can be resize: by resizing the canvas with css or by drawing the image at a smaller size.
See this question for more details.
i got this image by right clicking the canvas element in firefox and saving as.
var img = new Image();
img.onload = function () {
console.debug(this.width,this.height);
var canvas = document.createElement('canvas'), ctx;
canvas.width = 188;
canvas.height = 150;
document.body.appendChild(canvas);
ctx = canvas.getContext('2d');
ctx.drawImage(img,0,0,188,150);
};
img.src = 'original.jpg';
so anyway, here is a 'fixed' version of your example:
var img = new Image();
// added cause it wasnt defined
var canvas = document.createElement("canvas");
document.body.appendChild(canvas);
var ctx = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
// adding it to the body
document.body.appendChild(canvasCopy);
var copyContext = canvasCopy.getContext("2d");
img.onload = function()
{
var ratio = 1;
// defining cause it wasnt
var maxWidth = 188,
maxHeight = 150;
if(img.width > maxWidth)
ratio = maxWidth / img.width;
else if(img.height > maxHeight)
ratio = maxHeight / img.height;
canvasCopy.width = img.width;
canvasCopy.height = img.height;
copyContext.drawImage(img, 0, 0);
canvas.width = img.width * ratio;
canvas.height = img.height * ratio;
// the line to change
// ctx.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvas.width, canvas.height);
// the method signature you are using is for slicing
ctx.drawImage(canvasCopy, 0, 0, canvas.width, canvas.height);
};
// changed for example
img.src = 'original.jpg';
For resizing to image with width less that original, i use:
function resize2(i) {
var cc = document.createElement("canvas");
cc.width = i.width / 2;
cc.height = i.height / 2;
var ctx = cc.getContext("2d");
ctx.drawImage(i, 0, 0, cc.width, cc.height);
return cc;
}
var cc = img;
while (cc.width > 64 * 2) {
cc = resize2(cc);
}
// .. than drawImage(cc, .... )
and it works =).
I have a feeling the module I wrote will produce similar results to photoshop, as it preserves color data by averaging them, not applying an algorithm. It's kind of slow, but to me it is the best, because it preserves all the color data.
https://github.com/danschumann/limby-resize/blob/master/lib/canvas_resize.js
It doesn't take the nearest neighbor and drop other pixels, or sample a group and take a random average. It takes the exact proportion each source pixel should output into the destination pixel. The average pixel color in the source will be the average pixel color in the destination, which these other formulas, I think they will not be.
an example of how to use is at the bottom of
https://github.com/danschumann/limby-resize
UPDATE OCT 2018: These days my example is more academic than anything else. Webgl is pretty much 100%, so you'd be better off resizing with that to produce similar results, but faster. PICA.js does this, I believe. –
The problem with some of this solutions is that they access directly the pixel data and loop through it to perform the downsampling. Depending on the size of the image this can be very resource intensive, and it would be better to use the browser's internal algorithms.
The drawImage() function is using a linear-interpolation, nearest-neighbor resampling method. That works well when you are not resizing down more than half the original size.
If you loop to only resize max one half at a time, the results would be quite good, and much faster than accessing pixel data.
This function downsample to half at a time until reaching the desired size:
function resize_image( src, dst, type, quality ) {
var tmp = new Image(),
canvas, context, cW, cH;
type = type || 'image/jpeg';
quality = quality || 0.92;
cW = src.naturalWidth;
cH = src.naturalHeight;
tmp.src = src.src;
tmp.onload = function() {
canvas = document.createElement( 'canvas' );
cW /= 2;
cH /= 2;
if ( cW < src.width ) cW = src.width;
if ( cH < src.height ) cH = src.height;
canvas.width = cW;
canvas.height = cH;
context = canvas.getContext( '2d' );
context.drawImage( tmp, 0, 0, cW, cH );
dst.src = canvas.toDataURL( type, quality );
if ( cW <= src.width || cH <= src.height )
return;
tmp.src = dst.src;
}
}
// The images sent as parameters can be in the DOM or be image objects
resize_image( $( '#original' )[0], $( '#smaller' )[0] );
Credits to this post
So something interesting that I found a while ago while working with canvas that might be helpful:
To resize the canvas control on its own, you need to use the height="" and width="" attributes (or canvas.width/canvas.height elements). If you use CSS to resize the canvas, it will actually stretch (i.e.: resize) the content of the canvas to fit the full canvas (rather than simply increasing or decreasing the area of the canvas.
It'd be worth a shot to try drawing the image into a canvas control with the height and width attributes set to the size of the image and then using CSS to resize the canvas to the size you're looking for. Perhaps this would use a different resizing algorithm.
It should also be noted that canvas has different effects in different browsers (and even different versions of different browsers). The algorithms and techniques used in the browsers is likely to change over time (especially with Firefox 4 and Chrome 6 coming out so soon, which will place heavy emphasis on canvas rendering performance).
In addition, you may want to give SVG a shot, too, as it likely uses a different algorithm as well.
Best of luck!
Fast and simple Javascript image resizer:
https://github.com/calvintwr/blitz-hermite-resize
const blitz = Blitz.create()
/* Promise */
blitz({
source: DOM Image/DOM Canvas/jQuery/DataURL/File,
width: 400,
height: 600
}).then(output => {
// handle output
})catch(error => {
// handle error
})
/* Await */
let resized = await blizt({...})
/* Old school callback */
const blitz = Blitz.create('callback')
blitz({...}, function(output) {
// run your callback.
})
History
This is really after many rounds of research, reading and trying.
The resizer algorithm uses #ViliusL's Hermite script (Hermite resizer is really the fastest and gives reasonably good output). Extended with features you need.
Forks 1 worker to do the resizing so that it doesn't freeze your browser when resizing, unlike all other JS resizers out there.
I converted #syockit's answer as well as the step-down approach into a reusable Angular service for anyone who's interested: https://gist.github.com/fisch0920/37bac5e741eaec60e983
I included both solutions because they both have their own pros / cons. The lanczos convolution approach is higher quality at the cost of being slower, whereas the step-wise downscaling approach produces reasonably antialiased results and is significantly faster.
Example usage:
angular.module('demo').controller('ExampleCtrl', function (imageService) {
// EXAMPLE USAGE
// NOTE: it's bad practice to access the DOM inside a controller,
// but this is just to show the example usage.
// resize by lanczos-sinc filter
imageService.resize($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
// resize by stepping down image size in increments of 2x
imageService.resizeStep($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
})
Thanks #syockit for an awesome answer. however, I had to reformat a little as follows to make it work. Perhaps due to DOM scanning issues:
$(document).ready(function () {
$('img').on("load", clickA);
function clickA() {
var img = this;
var canvas = document.createElement("canvas");
new thumbnailer(canvas, img, 50, 3);
document.body.appendChild(canvas);
}
function thumbnailer(elem, img, sx, lobes) {
this.canvas = elem;
elem.width = img.width;
elem.height = img.height;
elem.style.display = "none";
this.ctx = elem.getContext("2d");
this.ctx.drawImage(img, 0, 0);
this.img = img;
this.src = this.ctx.getImageData(0, 0, img.width, img.height);
this.dest = {
width: sx,
height: Math.round(img.height * sx / img.width)
};
this.dest.data = new Array(this.dest.width * this.dest.height * 3);
this.lanczos = lanczosCreate(lobes);
this.ratio = img.width / sx;
this.rcp_ratio = 2 / this.ratio;
this.range2 = Math.ceil(this.ratio * lobes / 2);
this.cacheLanc = {};
this.center = {};
this.icenter = {};
setTimeout(process1, 0, this, 0);
}
//returns a function that calculates lanczos weight
function lanczosCreate(lobes) {
return function (x) {
if (x > lobes)
return 0;
x *= Math.PI;
if (Math.abs(x) < 1e-16)
return 1
var xx = x / lobes;
return Math.sin(x) * Math.sin(xx) / x / xx;
}
}
process1 = function (self, u) {
self.center.x = (u + 0.5) * self.ratio;
self.icenter.x = Math.floor(self.center.x);
for (var v = 0; v < self.dest.height; v++) {
self.center.y = (v + 0.5) * self.ratio;
self.icenter.y = Math.floor(self.center.y);
var a, r, g, b;
a = r = g = b = 0;
for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
if (i < 0 || i >= self.src.width)
continue;
var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
if (!self.cacheLanc[f_x])
self.cacheLanc[f_x] = {};
for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
if (j < 0 || j >= self.src.height)
continue;
var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
if (self.cacheLanc[f_x][f_y] == undefined)
self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2) + Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
weight = self.cacheLanc[f_x][f_y];
if (weight > 0) {
var idx = (j * self.src.width + i) * 4;
a += weight;
r += weight * self.src.data[idx];
g += weight * self.src.data[idx + 1];
b += weight * self.src.data[idx + 2];
}
}
}
var idx = (v * self.dest.width + u) * 3;
self.dest.data[idx] = r / a;
self.dest.data[idx + 1] = g / a;
self.dest.data[idx + 2] = b / a;
}
if (++u < self.dest.width)
setTimeout(process1, 0, self, u);
else
setTimeout(process2, 0, self);
};
process2 = function (self) {
self.canvas.width = self.dest.width;
self.canvas.height = self.dest.height;
self.ctx.drawImage(self.img, 0, 0);
self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
var idx, idx2;
for (var i = 0; i < self.dest.width; i++) {
for (var j = 0; j < self.dest.height; j++) {
idx = (j * self.dest.width + i) * 3;
idx2 = (j * self.dest.width + i) * 4;
self.src.data[idx2] = self.dest.data[idx];
self.src.data[idx2 + 1] = self.dest.data[idx + 1];
self.src.data[idx2 + 2] = self.dest.data[idx + 2];
}
}
self.ctx.putImageData(self.src, 0, 0);
self.canvas.style.display = "block";
}
});
I wanted some well defined functions out of answers here so ended up with these which am hoping would be useful for others also,
function getImageFromLink(link) {
return new Promise(function (resolve) {
var image = new Image();
image.onload = function () { resolve(image); };
image.src = link;
});
}
function resizeImageToBlob(image, width, height, mime) {
return new Promise(function (resolve) {
var canvas = document.createElement('canvas');
canvas.width = width;
canvas.height = height;
canvas.getContext('2d').drawImage(image, 0, 0, width, height);
return canvas.toBlob(resolve, mime);
});
}
getImageFromLink(location.href).then(function (image) {
// calculate these based on the original size
var width = image.width / 4;
var height = image.height / 4;
return resizeImageToBlob(image, width, height, 'image/jpeg');
}).then(function (blob) {
// Do something with the result Blob object
document.querySelector('img').src = URL.createObjectURL(blob);
});
Just for the sake of testing this run it on a image opened in a tab.
I just ran a page of side by sides comparisons and unless something has changed recently, I could see no better downsizing (scaling) using canvas vs. simple css. I tested in FF6 Mac OSX 10.7. Still slightly soft vs. the original.
I did however stumble upon something that did make a huge difference and that was using image filters in browsers that support canvas. You can actually manipulate images much like you can in Photoshop with blur, sharpen, saturation, ripple, grayscale, etc.
I then found an awesome jQuery plug-in which makes application of these filters a snap:
http://codecanyon.net/item/jsmanipulate-jquery-image-manipulation-plugin/428234
I simply apply the sharpen filter right after resizing the image which should give you the desired effect. I didn't even have to use a canvas element.
Looking for another great simple solution?
var img=document.createElement('img');
img.src=canvas.toDataURL();
$(img).css("background", backgroundColor);
$(img).width(settings.width);
$(img).height(settings.height);
This solution will use the resize algorith of browser! :)