原生nodeJS调整缓冲区图像大小

function lanczosCreate(lobes) {
    return function(x) {
        if (x > lobes)
            return 0;
        x *= Math.PI;
        if (Math.abs(x) < 1e-16)
            return 1;
        var xx = x / lobes;
        return Math.sin(x) * Math.sin(xx) / x / xx;
    };
}

// elem: canvas element,img: image element,sx: scaled width,lobes: kernel radius
function thumbnailer(elem,img,sx,lobes) {
    this.canvas = elem;
    elem.width = img.width;
    elem.height = img.height;
    elem.style.display = "none";
    this.ctx = elem.getcontext("2d");
    this.ctx.drawImage(img,0);
    this.img = img;
    this.src = this.ctx.getImageData(0,img.width,img.height);
    this.dest = {
        width : sx,height : Math.round(img.height * sx / img.width),};
    this.dest.data = new Array(this.dest.width * this.dest.height * 3);
    this.lanczos = lanczosCreate(lobes);
    this.ratio = img.width / sx;
    this.rcp_ratio = 2 / this.ratio;
    this.range2 = Math.ceil(this.ratio * lobes / 2);
    this.cacheLanc = {};
    this.center = {};
    this.icenter = {};
    setTimeout(this.process1,this,0);
}

thumbnailer.prototype.process1 = function(self,u) {
    self.center.x = (u + 0.5) * self.ratio;
    self.icenter.x = Math.floor(self.center.x);
    for (var v = 0; v < self.dest.height; v++) {
        self.center.y = (v + 0.5) * self.ratio;
        self.icenter.y = Math.floor(self.center.y);
        var a,r,g,b;
        a = r = g = b = 0;
        for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
            if (i < 0 || i >= self.src.width)
                continue;
            var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
            if (!self.cacheLanc[f_x])
                self.cacheLanc[f_x] = {};
            for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
                if (j < 0 || j >= self.src.height)
                    continue;
                var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
                if (self.cacheLanc[f_x][f_y] == undefined)
                    self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio,2)
                            + Math.pow(f_y * self.rcp_ratio,2)) / 1000);
                weight = self.cacheLanc[f_x][f_y];
                if (weight > 0) {
                    var idx = (j * self.src.width + i) * 4;
                    a += weight;
                    r += weight * self.src.data[idx];
                    g += weight * self.src.data[idx + 1];
                    b += weight * self.src.data[idx + 2];
                }
            }
        }
        var idx = (v * self.dest.width + u) * 3;
        self.dest.data[idx] = r / a;
        self.dest.data[idx + 1] = g / a;
        self.dest.data[idx + 2] = b / a;
    }

    if (++u < self.dest.width)
        setTimeout(self.process1,self,u);
    else
        setTimeout(self.process2,self);
};
thumbnailer.prototype.process2 = function(self) {
    self.canvas.width = self.dest.width;
    self.canvas.height = self.dest.height;
    self.ctx.drawImage(self.img,self.dest.width,self.dest.height);
    self.src = self.ctx.getImageData(0,self.dest.height);
    var idx,idx2;
    for (var i = 0; i < self.dest.width; i++) {
        for (var j = 0; j < self.dest.height; j++) {
            idx = (j * self.dest.width + i) * 3;
            idx2 = (j * self.dest.width + i) * 4;
            self.src.data[idx2] = self.dest.data[idx];
            self.src.data[idx2 + 1] = self.dest.data[idx + 1];
            self.src.data[idx2 + 2] = self.dest.data[idx + 2];
        }
    }
    self.ctx.putImageData(self.src,0);
    self.canvas.style.display = "block";
};

然后是图像（用var img = new Image(); img.src = "something"制作）：

img.onload = function() {
    var canvas = document.createElement("canvas");
    new thumbnailer(canvas,188,3); //this produces lanczos3
    // but feel free to raise it up to 8. Your client will appreciate
    // that the program makes full use of his machine.
    document.body.appendChild(canvas);
};

因此，首先，这在客户端非常慢，但是也许在服务器上可能会更快。需要更换/节点中不存在的东西是ctx.getImageData（可以用缓冲区复制）

有人知道在nodejs中从哪里开始，这在所有实际性能上都是明智的吗？如果不能，可以使用上述的C ++教程代码，通过纯node-gyp来提高性能吗？（如下）：

#include<iostream>

class RawBitMap
{
public:
    RawBitMap():_data(NULL),_width(0),_height(0)
    {};

    bool Initialise()
    {
        // Set a basic 2 by 2 bitmap for testing.
        //
        if(_data != NULL)
            delete[] _data;

        _width = 2;
        _height = 2;    
        _data = new unsigned char[ GetByteCount() ];

        //
        _data[0] = 0;   // Pixels(0,0) red value
        _data[1] = 1;   // Pixels(0,0) green value
        _data[2] = 2;   // Pixels(0,0) blue value
        _data[3] = 253; // Pixels(1,0)
        _data[4] = 254;
        _data[5] = 255;
        _data[6] = 253; // Pixels(0,1)
        _data[7] = 254;
        _data[8] = 255;
        _data[9] = 0;   // Pixels(1,1)
        _data[10] = 1;
        _data[11] = 2;  

        return true;
    }

    // Perform a basic 'pixel' enlarging resample.
    bool Resample(int newWidth,int newHeight)
    {
        if(_data == NULL) return false;
        //
        // Get a new buuffer to interpolate into
        unsigned char* newData = new unsigned char [newWidth * newHeight * 3];

        double scaleWidth =  (double)newWidth / (double)_width;
        double scaleHeight = (double)newHeight / (double)_height;

        for(int cy = 0; cy < newHeight; cy++)
        {
            for(int cx = 0; cx < newWidth; cx++)
            {
                int pixel = (cy * (newWidth *3)) + (cx*3);
                int nearestMatch =  (((int)(cy / scaleHeight) * (_width *3)) + ((int)(cx / scaleWidth) *3) );

                newData[pixel    ] =  _data[nearestMatch    ];
                newData[pixel + 1] =  _data[nearestMatch + 1];
                newData[pixel + 2] =  _data[nearestMatch + 2];
            }
        }

        //
        delete[] _data;
        _data = newData;
        _width = newWidth;
        _height = newHeight; 

        return true;
    }

    // Show the values of the Bitmap for demo.
    void ShowData()
    {
        std::cout << "Bitmap data:" << std::endl;
        std::cout << "============" << std::endl;
        std::cout << "Width:  " << _width  << std::endl;
        std::cout << "Height: " << _height  << std::endl;
        std::cout << "Data:" << std::endl;

        for(int cy = 0; cy < _height; cy++)
        {
            for(int cx = 0; cx < _width; cx++)
            {
                int pixel = (cy * (_width *3)) + (cx*3);
                std::cout << "rgb(" << (int)_data[pixel] << "," << (int)_data[pixel+1] << "," << (int)_data[pixel+2] << ") ";
            }
            std::cout << std::endl;
        }
        std::cout << "_________________________________________________________" << std::endl;
    }


    // Return the total number of bytes in the Bitmap.
    inline int GetByteCount()
    {
        return (_width * _height * 3);
    }

private:
    int _width;
    int _height;
    unsigned char* _data;

};


int main(int argc,char* argv[])
{
    RawBitMap bitMap;

    bitMap.Initialise();
    bitMap.ShowData();

    if (!bitMap.Resample(4,4))
        std::cout << "Failed to resample bitMap:" << std::endl ; 
    bitMap.ShowData();

    bitMap.Initialise();
    if (!bitMap.Resample(3,3))
        std::cout << "Failed to resample bitMap:" << std::endl ;
    bitMap.ShowData();


    return 0;
}

我想这是在创建2x2位图并调整其大小，但是基本原理仍然可以应用于纯node-gyp。还有其他人这样做吗？真的可行吗？

找到了一个简单，快速的方法，仅对节点使用pngjs库（它是用纯本机节点编写的，因此甚至可以对其进行优化），并内置了流库。因此，只需在代码顶部执行var PNG = require("pngjs").PNG,stream = require("stream");，然后使用以下代码：

function cobRes(iBuf,width,cb) {
        b2s(iBuf)
        .pipe(new PNG({
            filterType: -1
        }))
        .on('parsed',function() {

            var nw = width;
            var nh = nw *  this.height /this.width;
            var f = resize(this,nw,nh);

            sbuff(f.pack(),b=>{
                cb(b);
            })
        })


        function resize(srcPng,height) {
            var rez = new PNG({
                width:width,height:height
            });
            for(var i = 0; i < width; i++) {
                var tx = i / width,ssx = Math.floor(tx * srcPng.width);
                for(var j = 0; j < height; j++) {
                    var ty = j / height,ssy = Math.floor(ty * srcPng.height);
                    var indexO = (ssx + srcPng.width * ssy) * 4,indexC = (i + width * j) * 4,rgbaO = [
                            srcPng.data[indexO  ],srcPng.data[indexO+1],srcPng.data[indexO+2],srcPng.data[indexO+3]
                        ]
                    rez.data[indexC  ] = rgbaO[0];
                    rez.data[indexC+1] = rgbaO[1];
                    rez.data[indexC+2] = rgbaO[2];
                    rez.data[indexC+3] = rgbaO[3];
                }
            }
            return rez;
        }

        function b2s(b) {
            var str = new stream.Readable();
            str.push(b);
            str.push(null);
            return str;
        }
        function sbuff(stream,cb) {
            var bufs = []
            var pk = stream;
            pk.on('data',(d)=> {
                bufs.push(d);

            })
            pk.on('end',() => {
                var buff = Buffer.concat(bufs);
                cb(buff);
            });
        }
    }

然后使用：

cobRes(fs.readFileSync("somePNGfile.png"),200,buffer => fs.writeFileSync("new.png",buffer))

不确定为什么每个人都为此使用复杂的库：）

原生nodeJS调整缓冲区图像大小

nut0032 回答：原生nodeJS调整缓冲区图像大小

大家都在问