<!doctype html>

<html>

<head>

<meta charset="utf-8">

<title>无标题文档</title>

<script>

window.onload = function ()

{

    var oc = document.getElementById('c1');

    var ogc = oc.getContext('2d');

    var yimg = new Image();

    yimg.onload = function ()

    {

        draw(this);

    }

    yimg.src = 'img/5-5.jpg';

    function draw(obj)

    {

        oc.width = obj.width;

        oc.height = obj.height*2;

        ogc.drawImage(obj,0,0);

        var oimg = ogc.getImageData(0,0,obj.width,obj.height);

        var w = oimg.width;

        var h = oimg.height;

        var newimg = ogc.createImageData(obj.width,obj.height);

        for(var i = 0; i < h; i++)

        {

            for(var j = 0; j < w; j++)

            {

                var color = getXY(oimg,j,i)

                var result = [];

                result[0] = 255 - color[0];

                result[1] = 255 - color[1];

                result[2] = 255 - color[2];

                result[3] = 255*i/h;

                setXY(newimg,j,h-i,result);

            }

        }

        ogc.putImageData(newimg,0,obj.height);

    }

    function getXY(obj,x,y)

    {

        var w = obj.width;

        var h = obj.height;

        var d = obj.data;

        var color = [];

        color[0] = d[ 4*(y*w+x)];

        color[1] = d[ 4*(y*w+x) +1];

        color[2] = d[ 4*(y*w+x) +2];

        color[3] = d[ 4*(y*w+x) +3];

        return color;

    }

    function setXY(obj,x,y,color)

    {

        var w = obj.width;

        var h = obj.height;

        var d = obj.data;

        d[ 4*(y*w+x)] = color[0];

        d[ 4*(y*w+x) +1] = color[1];

        d[ 4*(y*w+x) +2] = color[2];

        d[ 4*(y*w+x) +3] = color[3];

    }

}

</script>

<style>

body{

    background:pink;

    }

#c1{

    background:white;

    }

</style>

</head>

<body>

<canvas id="c1" width="400" height="800"></canvas>

</body>

</html>

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