jorinvo · August 29, 2015 14:02
diff --git a/canvas-filter.html b/canvas-filter.html
 <!DOCTYPE html>
 <html>
 <head>
  <meta charset="UTF-8">
  <title>Demo for Basic Image Filtering Using a Canvas Element</title>
 </head>
 <body>

  <div>
    <input type="file" id="loader">
    <select id="filter">
      <option value="original">No Filter</option>
      <option value="lowpass">Soft Focus</option>
      <option value="highpass">Highpass</option>
      <option value="edges">Sharp Edges</option>
    </select>
    <a href="//gist.github.com/jorin-vogel/df70938d061b2b43c26d">view source</a>
  </div>

  <canvas id="pic"></canvas>



  <script>
  !function() {


    var width, height, i, x, y, r, g, b, xWithOffset, yWithOffset, pos, kernel, baseImageData;
    var pic = document.getElementById('pic');
    var ctx = pic.getContext('2d');
    var selectedFilter = 'original';


    function applyFilter() {

      var res = ctx.createImageData(baseImageData);
      var pixels = baseImageData.data;
      var filter  = filters[selectedFilter];

      for (y = 0; y < height; y++) {
        for (x = 0; x < width; x++) {

          r = g = b = 0;

          for (i = 0; i < kernelCoordinates.length; i += 2) {
            // restrict to pixels inside image
            xWithOffset = restrict( x + kernelCoordinates[i]   , width );
            yWithOffset = restrict( y + kernelCoordinates[i+1] , height );
            pos = 4 * ( yWithOffset * width + xWithOffset );
            kernel = filter.kernel[i/2];
            r += pixels[pos]    * kernel;
            g += pixels[pos+1]  * kernel;
            b += pixels[pos+2]  * kernel;
          }

          pos = 4 * ( y * width + x );

          res.data[pos]    = transform(r, filter);
          res.data[pos+1]  = transform(g, filter);
          res.data[pos+2]  = transform(b, filter);
          res.data[pos+3]  = pixels[pos+3]; // don't manipulate alpha value

        }
      }

      ctx.putImageData(res, 0, 0);

    }


    function loadImage(src) {
      var img = new Image();
      img.onload = function() {
        width  = pic.width  = img.width;
        height = pic.height = img.height;
        ctx.drawImage(img, 0, 0);
        baseImageData = ctx.getImageData(0, 0, width, height);
        applyFilter();
      };
      img.src = src;
    }



    //
    // FILTERS
    //

    var filters = {

      original: {
        kernel: [
          0, 0, 0,
          0, 1, 0,
          0, 0, 0
        ],
        scale: 1,
        offset: 0
      },

      lowpass: {
        kernel: [
          1, 1, 1,
          1, 1, 1,
          1, 1, 1
        ],
        scale: 9,
        offset: 0
      },

      highpass: {
        kernel: [
          -1, -1, -1,
          -1,  8, -1,
          -1, -1, -1
        ],
        scale: 9,
        offset: 128
      },

      edges: {
        kernel: [
          -1, -1, -1,
          -1,  17, -1,
          -1, -1, -1
        ],
        scale: 9,
        offset: 0
      }

    };



    //
    // HELPER
    //


    var kernelCoordinates = [
      -1, -1,
      0, -1,
      1, -1,
      -1, 0,
      0, 0,
      1, 0,
      -1, 1,
      0, 1,
      1, 1
    ];


    function restrict(val, max) {

      if (val < 0) return 0;
      if (val > max) return max;
      return val;
    }

    function transform(val, filter) {
      return restrict(val / filter.scale + filter.offset, 255);
    }



    //
    // USER EVENTS
    //

    document.getElementById('loader').addEventListener('change', function(changeEvent) {
      var reader = new FileReader();
      reader.onload = function(loadEvent) {
        loadImage(loadEvent.target.result);
      };
      reader.readAsDataURL(changeEvent.target.files[0]);
    });

    var filterElement = document.getElementById('filter');
    filterElement.addEventListener('change', function() {
      selectedFilter = filterElement.value;
      applyFilter();
    });



    //
    // INIT
    //

    loadImage('test.jpg');

  }();
  </script>

 </body>
 </html>
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="UTF-8">
	<title>Demo for Basic Image Filtering Using a Canvas Element</title>
	</head>
	<body>

	<div>
	<input type="file" id="loader">
	<select id="filter">
	<option value="original">No Filter</option>
	<option value="lowpass">Soft Focus</option>
	<option value="highpass">Highpass</option>
	<option value="edges">Sharp Edges</option>
	</select>
	<a href="//gist.github.com/jorin-vogel/df70938d061b2b43c26d">view source</a>
	</div>

	<canvas id="pic"></canvas>



	<script>
	!function() {


	var width, height, i, x, y, r, g, b, xWithOffset, yWithOffset, pos, kernel, baseImageData;
	var pic = document.getElementById('pic');
	var ctx = pic.getContext('2d');
	var selectedFilter = 'original';


	function applyFilter() {

	var res = ctx.createImageData(baseImageData);
	var pixels = baseImageData.data;
	var filter = filters[selectedFilter];

	for (y = 0; y < height; y++) {
	for (x = 0; x < width; x++) {

	r = g = b = 0;

	for (i = 0; i < kernelCoordinates.length; i += 2) {
	// restrict to pixels inside image
	xWithOffset = restrict( x + kernelCoordinates[i] , width );
	yWithOffset = restrict( y + kernelCoordinates[i+1] , height );
	pos = 4 * ( yWithOffset * width + xWithOffset );
	kernel = filter.kernel[i/2];
	r += pixels[pos] * kernel;
	g += pixels[pos+1] * kernel;
	b += pixels[pos+2] * kernel;
	}

	pos = 4 * ( y * width + x );

	res.data[pos] = transform(r, filter);
	res.data[pos+1] = transform(g, filter);
	res.data[pos+2] = transform(b, filter);
	res.data[pos+3] = pixels[pos+3]; // don't manipulate alpha value

	}
	}

	ctx.putImageData(res, 0, 0);

	}


	function loadImage(src) {
	var img = new Image();
	img.onload = function() {
	width = pic.width = img.width;
	height = pic.height = img.height;
	ctx.drawImage(img, 0, 0);
	baseImageData = ctx.getImageData(0, 0, width, height);
	applyFilter();
	};
	img.src = src;
	}



	//
	// FILTERS
	//

	var filters = {

	original: {
	kernel: [
	0, 0, 0,
	0, 1, 0,
	0, 0, 0
	],
	scale: 1,
	offset: 0
	},

	lowpass: {
	kernel: [
	1, 1, 1,
	1, 1, 1,
	1, 1, 1
	],
	scale: 9,
	offset: 0
	},

	highpass: {
	kernel: [
	-1, -1, -1,
	-1, 8, -1,
	-1, -1, -1
	],
	scale: 9,
	offset: 128
	},

	edges: {
	kernel: [
	-1, -1, -1,
	-1, 17, -1,
	-1, -1, -1
	],
	scale: 9,
	offset: 0
	}

	};



	//
	// HELPER
	//


	var kernelCoordinates = [
	-1, -1,
	0, -1,
	1, -1,
	-1, 0,
	0, 0,
	1, 0,
	-1, 1,
	0, 1,
	1, 1
	];


	function restrict(val, max) {

	if (val < 0) return 0;
	if (val > max) return max;
	return val;
	}

	function transform(val, filter) {
	return restrict(val / filter.scale + filter.offset, 255);
	}



	//
	// USER EVENTS
	//

	document.getElementById('loader').addEventListener('change', function(changeEvent) {
	var reader = new FileReader();
	reader.onload = function(loadEvent) {
	loadImage(loadEvent.target.result);
	};
	reader.readAsDataURL(changeEvent.target.files[0]);
	});

	var filterElement = document.getElementById('filter');
	filterElement.addEventListener('change', function() {
	selectedFilter = filterElement.value;
	applyFilter();
	});



	//
	// INIT
	//

	loadImage('test.jpg');

	}();
	</script>

	</body>
	</html>