使用 webworkers 和 canvas 合并 png 图像

Question

我正在尝试利用 web worker 将 png 数组合并为具有透明度的单个图像，就像 photoshop 在合并多个图层时所做的那样。

我这样做的原因是因为我将 olny 组合的结果保存到 indexeddb 中以供离线使用，然后我在 three.js 应用程序中使用该图像创建纹理.

场景是大约有 400 个产品，3d 平面上的纹理图像（产品）是 3 个图像（产品名称、价格和产品图像）的混合。

到目前为止我已经实现了这个，但是图像处理不是很好，我想知道如果我将 imageData.data

这是我目前拥有的，但我无法让它发挥作用。（这是在没有网络工作者的情况下完成的，现在只是试图使合并工作）

var images = [];
var imageData = [];

images.push( function ( callback ) {

    var mobile = new Image();

    mobile.onload = function () {
        console.log( "mobile loaded" );
        callback( null, mobile );
    };

    mobile.onerror = function ( e ) {
        console.log( "mobile error" );
        callback( e, null );
    };

    mobile.src = "mobile.png";

} );

images.push( function ( callback ) {

    var text = new Image();

    text.onload = function () {
        console.log( "text loaded" );
        callback( null, text );
    };

    text.onerror = function ( e ) {
        console.log( "text error" );
        callback( e, null );
    };

    text.src = "text.png";

} );

async.series( images, function ( err, results ) {

    if ( err ) {
        console.error( err );
    } else {
        console.log( results );
        getImageData( results );
    }

} );


var getImageData = function ( images ) {


    for ( var i = 0; i < images.length; i++ ) {

        var canvas = document.createElement( 'canvas' );

        canvas.width = 512;
        canvas.height = 512;

        var ctx = canvas.getContext( '2d' );

        ctx.drawImage( images[ i ], 0, 0 );

        imageData.push( ctx.getImageData( 0, 0, canvas.width, canvas.height ).data );

    }

    merge( imageData );

};

var merge = function ( data ) {

    var merged = [];
    var mixFactor = 0.5;

    //var newPixel = imageMainPixel * mixFactor + imageSecPixel * ( 1 - mixFactor )

    //for ( var i = 0, len = data.length; i < len; i++ ) {

    for ( var j = 0, byteLen = data[ 0 ].length; j < byteLen; j += 4 ) {

        var r = data[ 0 ][ j ] * mixFactor + data[ 1 ][ j ] * ( 1 - mixFactor );
        var g = data[ 0 ][ j + 1 ] * mixFactor + data[ 1 ][ j + 1 ] * ( 1 - mixFactor );
        var b = data[ 0 ][ j + 2 ] * mixFactor + data[ 1 ][ j + 2 ] * ( 1 - mixFactor );
        var a = data[ 0 ][ j + 3 ] * mixFactor + data[ 1 ][ j + 3 ] * ( 1 - mixFactor );

        merged[ j ] = r;
        merged[ j + 1 ] = g;
        merged[ j + 2 ] = b;
        merged[ j + 4 ] = a;

    }

    //}

    var canvas = document.getElementById( 'canvas' );
    canvas.width = 512;
    canvas.height = 512;
    var ctx = canvas.getContext( '2d' );
    var imageData = ctx.createImageData( 512, 512 );
    imageData.data.set( merged );
    ctx.putImageData( imageData, 0, 0 );

};

我目前遇到的错误是：

Uncaught RangeError: Source is too large

更新

我通过将我的合并功能更改为这个来设法合并图像：

var merge = function ( data ) {

    var canvas = document.getElementById( 'canvas' );
    canvas.width = 512;
    canvas.height = 512;
    var ctx = canvas.getContext( '2d' );
    var imageData = ctx.createImageData( 512, 512 );
    var mixFactor = 0.5;


    for ( var j = 0, byteLen = data[ 0 ].length; j < byteLen; j += 4 ) {

        imageData.data[ j ] = data[ 0 ][ j ] * mixFactor + data[ 1 ][ j ] * ( 1 - mixFactor );
        imageData.data[ j + 1 ] = data[ 0 ][ j + 1 ] * mixFactor + data[ 1 ][ j + 1 ] * ( 1 - mixFactor );
        imageData.data[ j + 2 ] = data[ 0 ][ j + 2 ] * mixFactor + data[ 1 ][ j + 2 ] * ( 1 - mixFactor );
        imageData.data[ j + 3 ] = data[ 0 ][ j + 3 ] * mixFactor + data[ 1 ][ j + 3 ] * ( 1 - mixFactor );

    }


    console.log( imageData.data.length );

    ctx.putImageData( imageData, 0, 0 );

};

结果是 2 张不透明度均为 50% 的图像。但这不是想要的结果。我只希望图像充当图层，例如将多个 png 一个放在另一个之上......如果顶部的那个有透明的地方，你应该能够看到它下面的图像。

也许我应该根据 alpha 值绘制？

Answer 1

经过一番思考，我最终检查了每个像素的 alpha 值，并设法完成了我想要的。我这样重写了合并函数：

var merge = function ( data ) {

    var canvas = document.getElementById( 'canvas' );
    canvas.width = 512;
    canvas.height = 512;
    var ctx = canvas.getContext( '2d' );
    var imageData = ctx.createImageData( 512, 512 );
    var mixFactor = 0.5;


    for ( var j = 0, byteLen = data[ 0 ].length; j < byteLen; j += 4 ) {

        // imageData.data[ j ] = data[ 0 ][ j ] * mixFactor + data[ 1 ][ j ] * ( 1 - mixFactor );
        // imageData.data[ j + 1 ] = data[ 0 ][ j + 1 ] * mixFactor + data[ 1 ][ j + 1 ] * ( 1 - mixFactor );
        // imageData.data[ j + 2 ] = data[ 0 ][ j + 2 ] * mixFactor + data[ 1 ][ j + 2 ] * ( 1 - mixFactor );
        // imageData.data[ j + 3 ] = data[ 0 ][ j + 3 ] * mixFactor + data[ 1 ][ j + 3 ] * ( 1 - mixFactor );

        imageData.data[ j ] = ( data[ 1 ][ j + 3 ] === 0 ? data[ 0 ][ j ] : data[ 1 ][ j ] );
        imageData.data[ j + 1 ] = ( data[ 1 ][ j + 3 ] === 0 ? data[ 0 ][ j + 1 ] : data[ 1 ][ j + 1 ] );
        imageData.data[ j + 2 ] = ( data[ 1 ][ j + 3 ] === 0 ? data[ 0 ][ j + 2 ] : data[ 1 ][ j + 2 ] );
        imageData.data[ j + 3 ] = ( data[ 1 ][ j + 3 ] === 0 ? data[ 0 ][ j + 3 ] : data[ 1 ][ j + 3 ] );

    }


    console.log( imageData.data.length );

    ctx.putImageData( imageData, 0, 0 );

};

仍然需要一些改进，但我想现在我将能够在网络工作者中合并图像:)

Answer 2

我写了a lib that handles this。不仅如此，它还能处理阴影和平铺。

Answer 3

修改后的代码为：

for ( var j = 0, byteLen = data[0].length; j < byteLen; j += 4 )
{
  var rA = data[0][j],   rB = data[1][j];
  var gA = data[0][j+1], gB = data[1][j+1];
  var bA = data[0][j+2], bB = data[1][j+2];
  var aA = data[0][j+3], aB = data[1][j+3];

  var rOut = (rA * aA / 255) + (rB * aB * (255 - aA) / (255*255));
  var gOut = (gA * aA / 255) + (gB * aB * (255 - aA) / (255*255));
  var bOut = (bA * aA / 255) + (bB * aB * (255 - aA) / (255*255));
  var aOut = aA + (aB * (255 - aA) / 255);

  imageData.data[j] = rOut;
  imageData.data[j+1] = gOut;
  imageData.data[j+2] = bOut;
  imageData.data[j+3] = aOut;

}

这是解决方案（Alpha 混合）How to mix two ARGB pixels?

使用 webworkers 和 canvas 合并 png 图像

Merge png images using webworkers and canvas

javascript

canvas

web-worker