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POUnable to get correct data from canvas getImageData
 

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  1. POUnable to get correct data from canvas getImageData
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    <p>This is in continuation to question <a href="https://stackoverflow.com/questions/16779437/how-to-get-pixel-data-from-canvas-which-contains-the-screenshot-generated-by-a-c/16783347">How to get pixel data from canvas which contains the screenshot generated by a chrome extension?</a> and the source code is available here <a href="https://github.com/whizzzkid/ColorHelper-Chrome/" rel="nofollow noreferrer">https://github.com/whizzzkid/ColorHelper-Chrome/</a></p> <p>The issue I am facing here is, the color I was expecting it to output is not correct and seems to be rather random values. Any help on this will be appreciated.</p> <pre><code>active = false; imgData = canvas = canvasContext = pixelData = ""; chrome.extension.onMessage.addListener(function(request, sender, sendResponse) { if(request.action == 'toggle'){ if(active){ active = false; $('#colorInfoContainer').remove(); console.log(active); }else{ active = true; $('body').prepend("&lt;div id=\"colorInfoContainer\" style=\"color: #000; text-align: center; top:0; width: 200px; position: fixed; left: 60%; margin-left: -100px; height: 15px; margin-top: -5px; -moz-border-radius: 5px; -webkit-border-radius: 5px; background: #fff; padding: 5px 5px 5px; font: bold 14px Arial; border: 3px solid; z-index: 999999999999;\"&gt;&lt;div id=\"colorInfo\" style=\"display: block;\"&gt;Color Info&lt;/div&gt;&lt;/div&gt;"); console.log(active); fill_canvas(); } } }); function fill_canvas(){ if(active){ chrome.extension.sendMessage({action: 'capture'}, function(response) { canvas = document.createElement('canvas'); canvas.width= document.documentElement.clientWidth; canvas.height= document.documentElement.clientHeight; canvasContext = canvas.getContext('2d'); var img = new Image(); img.onload = function(){ canvasContext.drawImage(img, 0, 0); } img.src = response.imageUrl; console.log(img.src); }); } } function getPosition(element) { var xPosition = 0; var yPosition = 0; while(element) { xPosition += (element.offsetLeft - element.scrollLeft + element.clientLeft); yPosition += (element.offsetTop - element.scrollTop + element.clientTop); element = element.offsetParent; } return { x: xPosition, y: yPosition }; } $(document).ready(function(){ setInterval(fill_canvas,1000); $(window).mousemove(function(e) { if(active){ //cache the position of canvas: var canvasPos = getPosition(canvas), dx = canvasPos.x, dy = canvasPos.y; //getting the correct color from pixels var x = e.clientX - dx, y = e.clientY - dy; //force x and y to stay within canvas: x = (x &lt; 0) ? 0 : (x &gt; canvas.width - 1) ? canvas.width - 1 : x; y = (y &lt; 0) ? 0 : (y &gt; canvas.height - 1) ? canvas.height - 1 : y; pixelData = canvasContext.getImageData(x, y, 1, 1).data; //console.log(canvasContext); //pixelData = canvasContext.getImageData(e.clientX,e.clientY, 1, 1).data; //console.log(x+','+y); console.log(pixelData); $('#colorInfoContainer').css('background-color','rgba('+pixelData[0]+', '+pixelData[1]+', '+pixelData[2]+', '+pixelData[3]+')') } }); }); </code></pre> <p>background.js</p> <pre><code>chrome.browserAction.onClicked.addListener(function(tab) { console.log('button clicked'); chrome.tabs.sendMessage(tab.id, { action: 'toggle' }); }); chrome.extension.onMessage.addListener(function(request, sender, sendResponse) { if (request.action == 'capture') { chrome.tabs.captureVisibleTab(null, { 'format':'png' }, function(dataUrl) { sendResponse({ imageUrl: dataUrl }); }); } return true; }); </code></pre> <p>The code mentioned above creates a div which should be of the same color as of the one under the mouse.</p> <p><strong>EDITS: updated according to updates from @Ken - Abdias Software. But still fails. help needed!</strong> Cheers!</p>
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    1. COPlease post the code in question as part of the post.
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    2. CO@Ken-AbdiasSoftware just did that!
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    3. CO@Ken-AbdiasSoftware updated according to updates from you But still fails. help needed!
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