performs a scale2x and scale3x operation on a HTML canvas

ScaleX

/*

JavaScript port of the following algorithm : http://scale2x.sourceforge.net/algorithm.html

*/

var scaleX = ( function( exports )
{

    function getPixel32( data, x,y,w )
    {
        var id = ( x + ( y * w ) ) * 4;
        return data[ id ] << 16 | data[ id + 1 ] << 8 | data[ id + 2 ];
    }

    function setPixel32( data, x,y,w, value )
    {
        var id = ( x + ( y * w ) ) * 4;
        data[ id ] = value >> 16 & 0xFF;
        data[ id + 1 ] = value >> 8 & 0xFF;
        data[ id + 2 ] = value & 0xFF;
        data[ id + 3 ] = 0xFF;
    }

    var can2x = document.createElement( "canvas" );
    var s2ctx  = can2x.getContext("2d");

    function scale2x( context )
    {


        var w = context.canvas.width;
        var h = context.canvas.height;
        var w2 = w * 2;

        var inputImageData = context.getImageData( 0,0,w,h );
        var inputData = inputImageData.data;

        can2x.width = w * 2;
        can2x.height = h * 2;
        var outputImageData = s2ctx.getImageData( 0,0,w*2,h*2 );
        var outputData = outputImageData.data;


        var E, E0, E1, E2, E3, B, D, F, H, i, j, i2, j2;
        for ( i = 0; i < w; i++ )
        {
            for ( j = 0; j < h; j++ )
            {

                E = getPixel32( inputData, i, j, w );

                //edges' handling
                if( i==0 || j==0 || i == w-1 || j == h-1 )
                {

                    E0 = E;
                    E1 = E;
                    E2 = E;
                    E3 = E;

                }else{

                    B = getPixel32( inputData, i, j-1, w );
                    D = getPixel32( inputData, i-1, j, w );
                    F = getPixel32( inputData, i+1, j, w );
                    H = getPixel32( inputData, i, j+1, w );

                    if (B != H && D != F )
                    {

                        E0 = ( D == B ) ? D : E;
                        E1 = ( B == F ) ? F : E;
                        E2 = ( D == H ) ? D : E;
                        E3 = ( H == F ) ? F : E;

                    }else{

                        E0 = E;
                        E1 = E;
                        E2 = E;
                        E3 = E;

                    }
                }

                i2 = i*2;
                j2 = j*2;
                setPixel32( outputData,   i2,   j2, w2, E0 );
                setPixel32( outputData, i2+1,   j2, w2, E1 );
                setPixel32( outputData,   i2, j2+1, w2, E2 );
                setPixel32( outputData, i2+1, j2+1, w2, E3 );

            }
        }

        outputImageData.data = outputData;
        s2ctx.putImageData( outputImageData,0,0 );
        return s2ctx;
    }


    var can3x = document.createElement( "canvas" );
    var s3ctx  = can3x.getContext("2d");

    function scale3x( context )
    {
        var w = context.canvas.width;
        var w3 = w * 3;
        var h = context.canvas.height;
        var h3 = h * 3;

        var inputImageData = context.getImageData( 0,0,w,h );
        var inputData = inputImageData.data;

        can3x.width = w * 3;
        can3x.height = h * 3;

        var outputImageData = s3ctx.getImageData( 0,0,w*3,h*3 );
        var outputData = outputImageData.data;

        var E, E0,E1,E2,E3,E4,E5,E6,E7,E8,A,B,C,D,F,G,H,I,i,j,i3,j3;
        for ( i = 0; i < w; i++ )
        {
            for ( j = 0; j < h; j++ )
            {

                E = getPixel32( inputData, i, j, w );

                //edges' handling
                if( i==0 || j==0 || i == w-1 || j == h-1 )
                {

                    E0 = E;
                    E1 = E;
                    E2 = E;
                    E3 = E;
                    E4 = E;
                    E5 = E;
                    E6 = E;
                    E7 = E;
                    E8 = E;

                }else{

                    A = getPixel32( inputData, i-1, j-1,w );
                    B = getPixel32( inputData,   i, j-1,w );
                    C = getPixel32( inputData,   i, j+1,w );
                    D = getPixel32( inputData, i-1,   j,w );
                    F = getPixel32( inputData, i+1,   j,w );
                    G = getPixel32( inputData, i-1, j+1,w );
                    H = getPixel32( inputData,   i, j+1,w );
                    I = getPixel32( inputData, i+1, j+1,w );

                    if ( B != H && D != F )
                    {

                        E0 = ( D == B ) ? D : E;
                        E1 = ( ( D == B && E != C ) || ( B == F && E != A ) ) ? B : E;
                        E2 = ( B == F )? F : E;
                        E3 = ( ( D == B && E != G ) || ( D == H && E != A ) ) ? D : E;
                        E4 = E;
                        E5 = ( ( B == F && E != I ) || ( H == F && E != C ) ) ? F : E;
                        E6 = ( D == H ) ? D : E;
                        E7 = ( ( D == H && E != I ) || ( H == F && E != G ) ) ? H : E;
                        E8 = ( H == F ) ? F : E;

                    } else {

                        E0 = E;
                        E1 = E;
                        E2 = E;
                        E3 = E;
                        E4 = E;
                        E5 = E;
                        E6 = E;
                        E7 = E;
                        E8 = E;

                    }
                }
                i3 = i*3;
                j3 = j*3;

                setPixel32( outputData,   i3, j3,   w3,   E0  );
                setPixel32( outputData, i3+1, j3,   w3,   E1  );
                setPixel32( outputData, i3+2, j3,   w3,   E2  );
                setPixel32( outputData,   i3, j3+1, w3,   E3  );
                setPixel32( outputData, i3+1, j3+1, w3,   E4  );
                setPixel32( outputData, i3+2, j3+1, w3,   E5  );
                setPixel32( outputData,   i3, j3+2, w3,   E6  );
                setPixel32( outputData, i3+1, j3+2, w3,   E7  );
                setPixel32( outputData, i3+2, j3+2, w3,   E8  );

            }
        }
        outputImageData.data = outputData;
        s3ctx.putImageData( outputImageData,0,0 );

        return s3ctx;
    }

    exports.scale2x = scale2x;
    exports.scale3x = scale3x;
    return exports;

}({}) );