Created
March 1, 2017 08:19
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Grayscaling and inverting colors
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<!-- Learn about this code on MDN: https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Pixel_manipulation_with_canvas --> | |
<canvas id="canvas" width="300" height="227"></canvas> | |
<div> | |
<input id="grayscalebtn" value="Grayscale" type="button"> | |
<input id="invertbtn" value="Invert" type="button"> | |
</div> |
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var img = new Image(); | |
img.src = 'https://mdn.mozillademos.org/files/5397/rhino.jpg'; | |
img.onload = function() { | |
draw(this); | |
}; | |
function draw(img) { | |
var canvas = document.getElementById('canvas'); | |
var ctx = canvas.getContext('2d'); | |
ctx.drawImage(img, 0, 0); | |
img.style.display = 'none'; | |
var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height); | |
var data = imageData.data; | |
var invert = function() { | |
for (var i = 0; i < data.length; i += 4) { | |
data[i] = 255 - data[i]; // red | |
data[i + 1] = 255 - data[i + 1]; // green | |
data[i + 2] = 255 - data[i + 2]; // blue | |
} | |
ctx.putImageData(imageData, 0, 0); | |
}; | |
var grayscale = function() { | |
for (var i = 0; i < data.length; i += 4) { | |
var avg = (data[i] + data[i + 1] + data[i + 2]) / 3; | |
data[i] = avg; // red | |
data[i + 1] = avg; // green | |
data[i + 2] = avg; // blue | |
} | |
ctx.putImageData(imageData, 0, 0); | |
}; | |
var invertbtn = document.getElementById('invertbtn'); | |
invertbtn.addEventListener('click', invert); | |
var grayscalebtn = document.getElementById('grayscalebtn'); | |
grayscalebtn.addEventListener('click', grayscale); | |
} |
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