getimagedata

问题 This question has been asked a lot, but I just don't understand why this is happening to me. Basically, I have a canvas, and an image, and when I try to do this: var canvas = document.getElementById('somecanvas'); var ctx = canvas.getContext('2d'); var someimage = document.createElement('img'); someimage.setAttribute('src', 'img/someimage.png'); someimage.onload = function(){ ctx.drawImage(someimage, 0, 0, canvas.width, canvas.height); data = ctx.getImageData(0,0,canvas.width,canvas.height);

问题 This question has been asked a lot, but I just don't understand why this is happening to me. Basically, I have a canvas, and an image, and when I try to do this: var canvas = document.getElementById('somecanvas'); var ctx = canvas.getContext('2d'); var someimage = document.createElement('img'); someimage.setAttribute('src', 'img/someimage.png'); someimage.onload = function(){ ctx.drawImage(someimage, 0, 0, canvas.width, canvas.height); data = ctx.getImageData(0,0,canvas.width,canvas.height);

问题 I'm doing a little HTML5 game and, while loading my sprites at the beginning of the map, I do some processing with GetImageData() / looping over all the image / PutImageData(). This works fantastically great on my PC, however, on my cell phones it's horrendously slow. PC: 5-6 ms iPhone 4: 300-600 ms Android HTC Desire S: 2500-3000 ms I've been doing some VERY basic benchmarking, and both GetImageData and PutImageData run very fast, what's taking long is the looping through the contents. Now,

问题 I have been trying to make a script that compares two images in HTML5 and Javascript. But for some odd reason, it always returns that the images are completely the same. And when looking at what the problem could be, I found out that every data value of every pixel returned, for some odd reason, "0". So, any idea of what I have done wrong? :) For some reason I feel like it's something very simple, but I just learned about the canvas element, so yeah. This is my code: function compareImg() {

问题 I have a two part question about javascript canvas: Part 1: I have a .jpg in the same file as my html document. I was wondering if there was a simple way of getting a pixel's color in that file without having to use context.getImageData(). Part 2: (If part 1 is too complex to be useful.) If I directly copy the code from this site: W3 schools getImageData() into an html file on my desktop, and add an image named img_the_scream.jpg to my desktop, then run it I get this error: Unable to get

问题 I'm very new to Html5 and I was wondering if someone could shed some light on this: <script type="text/javascript"> window.onload = function () { var canvas = document.getElementById('canvas'); //682 x 111 pixel canvas var context = canvas.getContext('2d'); var image = new Image(); image.src = "/Content/ImageTestOne/logo-for-dissolve.png"; //682 x 111 pixel image image.onload = function () { context.drawImage(image, 0, 0); drawFrame(); }; function drawFrame() { window.requestAnimationFrame

问题 My goal is to create an array of imageData from a series of png images. In order to do this I use a for loop to go through the images, put them in the canvas and then retrieve and store the created imageData in an array. The problem is that the image does not have enough time to be loaded in the canvas. My solution for now is to have a timer leave enough time but it's horrible. I can't seem to find any solution to this problem. Is there a way to have an "onload" function for the canvas? for

问题 If a 16-bit single channel (Gray-scale) raw pixel data losslessly encoded into Image format(e.g.PNG, Webp , Jpeg-2000 or JPEG-XR) and Image rendered to HTML5 canvas, then is there any way to retrieve original 16-bit Raw pixel data from the canvas? 回答1: No. When drawn to a canvas the image is uncompressed, and all the pixels data are pre-multiplied and converted to 24-bit data + an 8-bit alpha channel (RGBA). In this process the image looses everything from the original, even for same color

问题 So I've been working on a fun, online image effect program in javascript where the user enters a url to an image and hits 'enter', the image is drawn on the screen, and then the user can run some effects on it, such as g for greyscale, b for blur, etc. My problem is that the console prints out either: Redirect at origin [origin] has been blocked from loading by Cross-Origin Resource Sharing policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is

问题 I'd like to know if there is a way to dynamically modify/access the data contained in html images just as if they were an html5 canvas element. With canvas, you can in javascript access the raw pixel data with getImageData() and putImageData(), but I have thus far been not able to figure out how to do this with images. 回答1: // 1) Create a canvas, either on the page or simply in code var canvas = document.createElement('canvas'); var ctx = canvas.getContext('2d'); // 2) Copy your image data