I saw that you have helped David with his mirroring canvas problem before. Canvas - flip half the image
I have a similar problem and hope that maybe you could help me.
I want to apply the same mirror effect on my webcam-canvas, but instead of the left side, I want to take the RIGHT half of the image, flip it and apply it to the LEFT.
This is the code you've posted for David. It also works for my webcam cancas. Now I tried to change it, so that it works for the other side, but unfortunately I'm not able to get it.
for(var y = 0; y < height; y++) {
for(var x = 0; x < width / 2; x++) { // divide by 2 to only loop through the left half of the image.
var offset = ((width* y) + x) * 4; // Pixel origin
// Get pixel
var r = data[offset];
var g = data[offset + 1];
var b = data[offset + 2];
var a = data[offset + 3];
// Calculate how far to the right the mirrored pixel is
var mirrorOffset = (width - (x * 2)) * 4;
// Get set mirrored pixel's colours
data[offset + mirrorOffset] = r;
data[offset + 1 + mirrorOffset] = g;
data[offset + 2 + mirrorOffset] = b;
data[offset + 3 + mirrorOffset] = a;
}
}
Even if the accepted answer you're relying on uses imageData, there's absolutely no use for that.
Canvas allows, with drawImage and its transform (scale, rotate, translate), to perform many operations, one of them being to safely copy the canvas on itself.
Advantages is that it will be way easier AND way way faster than handling the image by its rgb components.
I'll let you read the code below, hopefully it's commented and clear enough.
The fiddle is here :
http://jsbin.com/betufeha/2/edit?js,output
One output example - i took also a mountain, a Canadian one :-) - :
Original :
Output :
html
<canvas id='cv'></canvas>
javascript
var mountain = new Image() ;
mountain.onload = drawMe;
mountain.src = 'http://www.hdwallpapers.in/walls/brooks_mountain_range_alaska-normal.jpg';
function drawMe() {
var cv=document.getElementById('cv');
// set the width/height same as image.
cv.width=mountain.width;
cv.height = mountain.height;
var ctx=cv.getContext('2d');
// first copy the whole image.
ctx.drawImage(mountain, 0, 0);
// save to avoid messing up context.
ctx.save();
// translate to the middle of the left part of the canvas = 1/4th of the image.
ctx.translate(cv.width/4, 0);
// flip the x coordinates to have a mirror effect
ctx.scale(-1,1);
// copy the right part on the left part.
ctx.drawImage(cv,
/*source */ cv.width/2,0,cv.width/2, cv.height,
/*destination*/ -cv.width/4, 0, cv.width/2, cv.height);
// restore context
ctx.restore();
}
Related
I'm trying to make a text effect similar to the effect found at the bottom of this article
My proposed approach is:
Make two canvasses, one is visible, the other is invisible I use this as a buffer.
Draw some text on the buffer canvas
Loop over getImageData pixels
if pixel alpha is not equal to zero (when there is a pixel drawn on the canvas buffer) with a small chance, ie 2%, draw a randomly generated circle with cool effecs at that pixel on the visible canvas.
I'm having trouble at step 4. With the code below, I'm trying to replicate the text on the second canvas, in full red. Instead I get this weird picture.
code
// create the canvas to replicate the buffer text on.
var draw = new Drawing(true);
var bufferText = function (size, textFont) {
// set the font to Georgia if it isn't defined
textFont = textFont || "Georgia";
// create a new canvas buffer, true means that it's visible on the screen
// Note, Drawing is a small library I wrote, it's just a wrapper over the canvas API
// it creates a new canvas and adds some functions to the context
// it doesn't change any of the original functions
var buffer = new Drawing(true);
// context is just a small wrapper library I wrote to make the canvas API a little more bearable.
with (buffer.context) {
font = util.format("{size}px {font}", {size: size, font: textFont});
fillText("Hi there", 0, size);
}
// get the imagedata and store the actual pixels array in data
var imageData = buffer.context.getImageData(0, 0, buffer.canvas.width, buffer.canvas.height);
var data = imageData.data;
var index, alpha, x, y;
// loop over the pixels
for (x = 0; x < imageData.width; x++) {
for (y = 0; y < imageData.height; y++) {
index = x * y * 4;
alpha = data[index + 3];
// if the alpha is not equal to 0, draw a red pixel at (x, y)
if (alpha !== 0) {
with (draw.context) {
dot(x/4, y/4, {fillColor: "red"})
}
}
}
}
};
bufferText(20);
Note that here, my buffer is actually visible to show where the red pixels are supposed to go compared to where they actually go.
I'm really confused by this problem.
If anybody knows an alternative approach, that's very welcome too.
replace this...
index = x * y * 4;
with...
index = (imageData.width * y) + x;
the rest is good :)
I'm trying to implement ColorPicker using Canvas just for fun. But i seem lost. as my browser is freezing for a while when it loads due to all these for loops.
I'm adding the screenshot of the result of this script:
window.onload = function(){
colorPicker();
}
function colorPicker(){
var canvas = document.getElementById("colDisp"),
frame = canvas.getContext("2d");
var r=0,
g=0,
b= 0;
function drawColor(){
for(r=0;r<255;r++){
for(g=0;g<255;g++){
for(b=0;b<255;b++){
frame.fillStyle="rgb("+r+","+g+","+b+")";
frame.fillRect(r,g,1,1);
}
}
}
}
drawColor();
Currently , i only want a solution about the freezing problem with better algorithm and it's not displaying the BLACK and GREY colors.
Please someone help me.
Instead of calling fillRect for every single pixel, it might be a lot more efficient to work with a raw RGBA buffer. You can obtain one using context.getImageData, fill it with the color values, and then put it back in one go using context.putImageData.
Note that your current code overwrites each single pixel 255 times, once for each possible blue-value. The final pass on each pixel is 255 blue, so you see no grey and black in the output.
Finding a good way to map all possible RGB values to a two-dimensional image isn't trivial, because RGB is a three-dimensional color-space. There are a lot of strategies for doing so, but none is really optimal for any possible use-case. You can find some creative solutions for this problem on AllRGB.com. A few of them might be suitable for a color-picker for some use-cases.
If you want to fetch the rgba of the pixel under the mouse, you must use context.getImageData.
getImageData returns an array of pixels.
var pixeldata=context.getImageData(0,0,canvas.width,canvas.height);
Each pixel is defined by 4 sequential array elements.
So if you have gotten a pixel array with getImageData:
// first pixel defined by the first 4 pixel array elements
pixeldata[0] = red component of pixel#1
pixeldata[1] = green component of pixel#1
pixeldata[2] = blue component of pixel#1
pixeldata[4] = alpha (opacity) component of pixel#1
// second pixel defined by the next 4 pixel array elements
pixeldata[5] = red component of pixel#2
pixeldata[6] = green component of pixel#2
pixeldata[7] = blue component of pixel#2
pixeldata[8] = alpha (opacity) component of pixel#2
So if you have a mouseX and mouseY then you can get the r,g,b,a values under the mouse like this:
// get the offset in the array where mouseX,mouseY begin
var offset=(imageWidth*mouseY+mouseX)*4;
// read the red,blue,green and alpha values of that pixel
var red = pixeldata[offset];
var green = pixeldata[offset+1];
var blue = pixeldata[offset+2];
var alpha = pixeldata[offset+3];
Here's a demo that draws a colorwheel on the canvas and displays the RGBA under the mouse:
http://jsfiddle.net/m1erickson/94BAQ/
A way to go, using .createImageData():
window.onload = function() {
var canvas = document.getElementById("colDisp");
var frame = canvas.getContext("2d");
var width = canvas.width;
var height = canvas.height;
var imagedata = frame.createImageData(width, height);
var index, x, y;
for (x = 0; x < width; x++) {
for (y = 0; y < height; y++) {
index = (x * width + y) * 4;
imagedata.data[index + 0] = x;
imagedata.data[index + 1] = y;
imagedata.data[index + 2] = x + y - 255;
imagedata.data[index + 3] = 255;
}
}
frame.putImageData(imagedata, 0, 0);
};
http://codepen.io/anon/pen/vGcaF
I want to resize image using very simple algorithm. I have something like this:
var offtx = document.createElement('canvas').getContext('2d');
offtx.drawImage(imageSource, offsetX, offsetY, width, height, 0, 0, width, height);
this.imageData = offtx.getImageData(0, 0, width, height).data;
offtx.clearRect(0, 0, width, height);
for(var x = 0; x < this.width; ++x)
{
for(var y = 0; y < this.height; ++y)
{
var i = (y * this.width + x) * 4;
var r = this.imageData[i ];
var g = this.imageData[i+1];
var b = this.imageData[i+2];
var a = this.imageData[i+3];
offtx.fillStyle = "rgba("+r+","+g+","+b+","+(a/255)+")";
offtx.fillRect(0.5 + (x * this.zoomLevel) | 0, 0.5 + (y*this.zoomLevel) | 0, this.zoomLevel, this.zoomLevel);
}
}
this.imageData = offtx.getImageData(0, 0, this.width * this.zoomLevel, this.height * this.zoomLevel);
However, the problem I have with this solution, is that the image looses any transparency information that way. I don't know if this happens somewere in this algorithm, or maybe putImageData that I am using later to display that image is doing this, but I can't seem to be able to preserve transparency.
Each time I do this I create a canvas, I put the image on that canvas and use getImageData to get image from that canvas as you can see in the first lines of the code. Maybe there is no other way, so I might not mind that...
But the problem is I use two for loops to draw resized image and then use getImageData to store that image information. This is a wierd way to do it. I would prefer to create empty image data and fill it with all the original image information only resized. I can't grasp that with my mind, I can't image the loop structure for this. To show what I mean:
for(var x = 0; x < this.width; ++x)
{
for(var y = 0; y < this.height; ++y)
{
var i = (y * this.width + x) * 4;
var r = this.imageData[i ];
var g = this.imageData[i+1];
var b = this.imageData[i+2];
var a = this.imageData[i+3];
//I WOULD LIKE MAGIC TO HAPPEN HERE THAT WILL
//RESIZE THAT CURRENT PIXEL AND MOVE IT TO THE NEW IMAGE DATA RESIZED
//SO EVERYTHING IS DONE NICE AND CLEAN IN THIS LOOP WITHOUT THE
//GETIMAGEDATA LATER AND MAYBE SET TRANSPARENT PIXELS WHILE I'M AT IT
}
}
I can't figure out the MAGIC part.
Thank you for reading!
Why not just use the built-in drawImage combined with image smoothing disabled? Doing this operation in a loop is not only relative slow but also prone to errors (as you already discovered).
Doing it the following way will give you the "pixel art" look and will also preserve the alpha channel:
var factor = 4; /// will resize 4x
offtx.imageSmoothingEnabled = false; /// prefixed in some browsers
offtx.drawImage(imageSource, offsetX, offsetY, width, height,
0, 0, width * factor, height * factor);
Here is an online demo.
Try using this library I recently made which can load an image, resize it fixed width & height or precentage.
It does exactly what you need, and much more like converting canvas to base64, blob, etc...
var CanvaWork = new CanvaWork();
CanvaWork.canvasResizeAll(obj.canvas, function(canvases){
// "canvases" will be an array containing 3 canvases with different sizes depending on initial options
});
https://github.com/vnbenny/canvawork.js
Hope this helps you!
I know how to get this height of a font:
By placing the text in a div and getting offset height of the div.
But I would like to get this actual height (Which will depend on font family):
Is that in any way possible using web based programming?
Is there a simple solution? I think the answer is no.
If you're ok with a more involved (and processor-intensive) solution, you could try this:
Render the text to a canvas, then use canvasCtx.getImageData(..) to retrieve pixel information. Next you would do something similar to what this pseudo code describes:
first_y : null
last_y : null
for each y:
for each x:
if imageData[x][y] is black:
if first_y is null:
first_y = y
last_y = y
height = last_y - first_y
This basically looks for the top (lowest y-index) of the lettering (black pixels) and the bottom (highest y-index) then subtracts to retrieve the height.
I was writing the code while Jason answered, but I decided to post it anyway:
http://jsfiddle.net/adtn8/2/
If you follow the comments you should get the idea what's going on and why. It works pretty fast and it's not so complicated as it may sound. Checked with GIMP and it is accurate.
(code to be sure it wont be lost):
// setup variables
var c = document.createElement('canvas'),
div = document.getElementsByTagName('div')[0],
out = document.getElementsByTagName('output')[0];
// set canvas's size to be equal with div
c.width = div.offsetWidth;
c.height = div.offsetHeight;
var ctx = c.getContext('2d');
// get div's font from computed style and apply it to context
ctx.font = window.getComputedStyle(div).font;
// use color other than black because all pixels are 0 when black and transparent
ctx.fillStyle = '#bbb';
// draw the text near the bottom of the canvas
ctx.fillText(div.innerText, 0, div.offsetHeight);
// loop trough the canvas' data to find first colored pixel
var data = ctx.getImageData(0, 0, c.width, c.height).data,
minY = 0, len = data.length;
for (var i = 0; i < len; i += 4) {
// when you found it
if (data[i] != 0) {
// get pixel's y position
minY = Math.floor(i / 4 / c.width);
break;
}
}
// and print out the results
out.innerText = c.height - minY + 'px';
EDIT:
I even made jQuery plugin for this: https://github.com/maciek134/jquery-textHeight
Enjoy.
In the creation of my html5 game engine I've been able to do some nice things and get some cool features. On a contract to make a game I've been asked to see if I can remove the background color from sprite images. And I see the pluses with this since we could use jpgs instead on pngs and decrease the size of the images.
Is there any way I can do this with pure javascript? I'd like to be able to do this without using the a canvas element so it can be faster, but if I have to that's okay.
If I have to do that I have another question, I don't want the canvas object to show that I use, can I use a canvas object with document.createElement without applying it to the document? That would be nice since it wouldn't have to be rendered to the webpage. If not I guess I can just move the canvas object to the left out of view.
Lastly do you think a good way to preprocess the images be to send them to a server cgi script and have it return a json pixel array?
Here is the function for floodfill algorithm, it removed the background from an image which is already drawn on the canvas.
In the following code canvas is the HTML5 canvas element and context it canvas.getContext("2d"). You can change the value of colorRange and try the function with different colors. The last line of the function
imageElement.src=canvas.toDataURL("image/png");
is to show the image inside an img tag. So you need an img and a canvas on your page. If you don't want to show the image in img element just remove the last line.
// Remove backgroud without ajax call, can be used in non IE browsers.
function RemoveBackground(){
var startR,startG,startB;
var canvasData;
var canvasWidth=canvas.width;
var canvasHeight=canvas.height;
canvasData=mainContext.getImageData(0,0,canvasWidth,canvasHeight);
startR = canvasData.data[0];
startG = canvasData.data[1];
startB = canvasData.data[2];
if(startR==0&& startG==0 && startR==0) return;
var pixelStack = [[0, 0]];
while(pixelStack.length)
{
var newPos, x, y, pixelPos, reachLeft, reachRight;
newPos = pixelStack.pop();
x = newPos[0];
y = newPos[1];
pixelPos = (y*canvasWidth + x) * 4;
while(y-- >= 0 && matchStartColor(pixelPos,canvasData,startR,startG,startB)){
pixelPos -= canvasWidth * 4;
}
pixelPos += canvasWidth * 4;
++y;
reachLeft = false;
reachRight = false;
while(y++ < canvasHeight-1 && matchStartColor(pixelPos,canvasData,startR,startG,startB))
{
colorPixel(pixelPos,canvasData);
if(x > 0)
{
if(matchStartColor(pixelPos-4,canvasData,startR,startG,startB))
{
if(!reachLeft){
pixelStack.push([x - 1, y]);
reachLeft = true;
}
}
else if(reachLeft)
{
reachLeft = false;
}
}
if(x < canvasWidth-1)
{
if(matchStartColor(pixelPos+4,canvasData,startR,startG,startB))
{
if(!reachRight)
{
pixelStack.push([x + 1, y]);
reachRight = true;
}
}
else if(reachRight)
{
reachRight = false;
}
}
pixelPos += canvasWidth * 4;
}
}
context.putImageData(canvasData, 0, 0);
imageElement.src=canvas.toDataURL("image/png");
}
// Helper function for remove background color.
function matchStartColor(pixelPos,canvasData,startR,startG,startB)
{
var r = canvasData.data[pixelPos];
var g = canvasData.data[pixelPos+1];
var b = canvasData.data[pixelPos+2];
var colorRange=8;
return ((r >= startR-colorRange && r<=startR+colorRange)
&&( g >= startG-colorRange && g<=startG+colorRange)
&&( b >= startB-colorRange && b<= startB+colorRange));
}
// Helper function for remove background color.
function colorPixel(pixelPos,canvasData)
{
canvasData.data[pixelPos] = 255;
canvasData.data[pixelPos+1] = 255;
canvasData.data[pixelPos+2] = 255;
}
Removing background without choppy borders isn't a trivial task, even by hand in image-editing programs. You'll have to implement some sort of antialiasing, at least.
Moreover, it's not a good idea to manipulate an image compressed into a lossy format.
PNG compression is superior (in terms of size) to JPG on simpler images with continuous fill of the same color and certain types of gradients. JPG is only good for heterogeneous images with lots of different colors mixed in unpredictable manner. Like photos. Which one would not expect in game sprites, I guess. And again – JPG is a lossy format.
As for the Canvas element, it doesn't have to be added to the DOM tree at all.
The most naïve algorithm to make a given color transparent would be such: draw the image, get its pixel data, iterate over the data and compare every pixel color with your given color. If it matches, set the alpha to 0.
Canvas API methods you'll need:
drawImage
getImageData
The somewhat tricky in it's simplicity part is the CanvasPixelArray. To check each pixel in such arrays, you do something like that:
for (var i = 0; i < pixelAr.length; i += 4) {
var r = pixelAr[i];
var g = pixelAr[i + 1];
var b = pixelAr[i + 2];
var alpha = pixelAr[i + 3];
}
Personally I would not go down this path. JPEG images are compressed, which means that whatever you define as a background color may change slightly in the compressed file (ie. you'll get the classic JPEG artifacting). Furthermore, you won't be able to support partial transparency unless you define a range for your background color, which in turn makes the editing more complicated. The tradeoff between file size and performance/quality is nowhere near worth it here, in my opinion.
Having said that, the only way you can access the pixel data from an image is by placing it on a canvas first. You can, as you mentioned, work with the canvas off-screen in memory without having to append it to the document.
If I understand your last question correctly, you cannot work with a canvas element on the server side. To work with pixel data on your server, you'd have to use something like PHP's image library.
If all of that doesn't sway you in favor of just using PNG images, here's some sample code that will remove a specified background color from a loaded image:
$(document).ready(function() {
var matte_color = [0, 255, 0, 255]; // rgba: [0, 255];
// Handles the loaded image element by erasing the matte color
// and appending the transformed image to the document.
function handleLoadedImage() {
eraseMatte(); // Eliminate the matte.
// Append the canvas element to the document where it is needed.
document.getElementById("parent_container").appendChild(canvas);
}
// Given the matte color defined at the top, clear all pixels to 100% transparency
// within the loaded sprite.
function eraseMatte() {
canvas.width = sprite.width;
canvas.height = sprite.height;
context.drawImage(sprite, 0, 0); // Draw the image on the canvas so we can read the pixels.
// Get the pixel data from the canvas.
var image_data = context.getImageData(0, 0, sprite.width, sprite.height);
var data = image_data.data; // Obtaining a direct handle is a huge performance boost.
var end = sprite.width * sprite.height * 4; // W x H x RGBA
// Loop over each pixel from the image and clear matte pixels as needed.
for (var i = 0; i < end; i += 4) {
if (data[i] == matte_color[0] && data[i + 1] == matte_color[1] &&
data[i + 2] == matte_color[2] && data[i + 3] == matte_color[3]) { // Color match.
data[i] = data[i + 1] = data[i + 2] = data[i + 3] = 0; // Set pixel to transparent.
}
}
// Put the transformed image data back on the canvas.
context.putImageData(image_data, 0, 0);
}
var canvas = document.createElement("canvas");
var context = canvas.getContext("2d");
var sprite = new Image();
sprite.onload = handleLoadedImage;
sprite.src = "sprite.jpg";
});
You can do that using a canvas, don't know if it is possible without it.
An easy way to achieve what you are trying to do is using the getImageData on your canvas's context:
imgData = myCanvasContext.getImageData(x1, y1, x2, y2);
x1, y1, x2, y2 are the coordenates of the area you want to get data, for the whole use 0, 0, width, height image. The getImageData will return you an ImageData, wich contains an array with rgba values from each pixel. The values will be ordered like this:
http://i.stack.imgur.com/tdHNJ.png
You can manipulate the array imgData.data[index], editing it values and, consequently, editing the image.
Here is a good article about editing images on html5 with canvas:
http://beej.us/blog/2010/02/html5s-canvas-part-ii-pixel-manipulation/
To doesn't show what you are doing, just create the canvas with the css command display:none;
(...)if I can remove the background color from sprite images. And I see the pluses with this since we could use jpgs instead on pngs(...)
I really recommend you to not do that. The jpg compression of the image can make image editing very hard. Removing the background of a jpg image isn't is easy, and it gets harder with the amount of borders on the image. I'm don't think the size that you will economize will compensate the hard work to remove a background from a jpg image.
Not exactly the same, but you can achieve that. I can give you an headstart on this - checkout this jsFiddle. I built this editor using FabricJS.
var canvas = new fabric.Canvas('c');
var imgInstance = new fabric.Image(imgElement);
canvas.add(imgInstance);//initialize the Canvas with the image