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How to Transition an Image from B&W to Color with Canvas

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Recently, in the CodeCanyon forums, a question was brought up: “How do I transition an image from black and white, to color — using only one image?” Unfortunately, at this point in time, it’s not possible with CSS. However, if we’re creative with javascript and canvas, we can create a solution relatively easily. I’ll show you how in today’s video tutorial!





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Final Source



<!DOCTYPE html>

<html lang="en">
<head>
<meta charset="utf-8">
<title>untitled</title>
<style>
/* Setup...not important. */
.img-wrap {
width: 500px;
margin: 100px auto;
position: relative;
cursor: pointer;
}

/* Handles animation of b*w to color */
canvas {
position: absolute;
left: 0;
top: 0;
opacity: 1;
-webkit-transition: all 1s;
-moz-transition: all 1s;
-o-transition: all 1s;
-ms-transition: all 1s;
transition: all 1s;
}

canvas:hover {
opacity: 0;
}

/* If you MUST have IE support */
#cvs-src {
filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
}

#cvs-src:hover {
filter: none;
}
</style>
</head>
<body>

<div class="img-wrap">
<img id="cvs-src" src="your-image.jpg" />
<canvas width=500 height=500></canvas>
</div>

<script>
(function() {
var supportsCanvas = !!document.createElement('canvas').getContext;
supportsCanvas && (window.onload = greyImages);

function greyImages() {
var ctx = document.getElementsByTagName("canvas")[0].getContext('2d'),
img = document.getElementById("cvs-src"),
imageData, px, length, i = 0,
grey;

ctx.drawImage(img, 0, 0);

// Set 500,500 to the width and height of your image.
imageData = ctx.getImageData(0, 0, 500, 500);
px = imageData.data;
length = px.length;

for ( ; i < length; i+= 4 ) {
grey = px[i] * .3 + px[i+1] * .59 + px[i+2] * .11;
px[i] = px[i+1] = px[i+2] = grey;
}

ctx.putImageData(imageData, 0, 0);
}
})();
</script>

</body>
</html>



Conclusion


So what do you think? Would you use this technique in your own projects? Can you think of a better way that doesn’t involve using a server-side language or sprites? Let me know in the comments!

How to Transition an Image from B&W to Color with Canvas

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