html - Image Reading from base64 data in javascript produces image of different size -

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i trying screenshot of page using chrome extension , trying crop image. upon taking screenshot, base64 dataurl of image.

when try render image using dataurl, image renders larger(appears zoomed in) original image. when manually give <img> object original size renders fine. when draw image canvas, canvas takes enlarged size.

i have been banging head against wall solution problem no avail. appreciated.

//here js code: var image = document.getelementbyid("image"); var canvas = document.getelementbyid('mycanvas'); var context = canvas.getcontext('2d');  image.onload = function() {     var sourcex = 0;     var sourcey = 0;     var sourcewidth = 150;     var sourceheight = 80;     var destwidth = sourcewidth;     var destheight = sourceheight;     var destx = 0;     var desty = 0;      context.drawimage(image, sourcex, sourcey, sourcewidth, sourceheight, destx, desty, destwidth, destheight); };

and here html code, removing dataurl takes space, , pasting url.

<!doctype html> <html> <head>   <meta charset="utf-8">   <meta name="viewport" content="width=device-width">   <title>js bin</title> </head> <body>   <img height = "678" width = "1280" id = "image" src = "http://s12.postimg.org/7r9q3h2vx/ss2.jpg"/>   <canvas id="mycanvas" width="500" height="200"></canvas> </body> </html>

the following image(from dataurl) want crop:

image dataurl. motive crop section of image

the following cropped image get. not intended image because appears enlarged(zoomed in). top left section of original image.

cropped image

for further reference, here jsbin link: https://jsbin.com/pomayowara/edit?output

the base64 dataurl provided has information image of 2560 × 1356, rescaling image 1280x678. code obtaining original size of image , therefore being enlarged. need send canvas original ratio of image , not resized dimensions of image.


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