HTML5 canvas：有没有办法使用“最近邻居”调整图像大小重新采样？

Question

我有一些 JS 对图像进行一些操作。我想要类似像素艺术的图形，所以我必须在图形编辑器中放大原始图像。 但我认为用小图像进行所有操作然后使用 html5 功能放大它是个好主意。这将节省大量处理时间（因为现在我的演示（警告：域名可能会导致工作中出现一些问题等）例如，在 Firefox 中加载时间非常长）。 但是当我尝试调整图像大小时，它会以双三次方式重新采样。如何使其在不重新采样的情况下调整图像大小？有没有跨浏览器的解决方案？

Answer 1

image-rendering: -webkit-optimize-contrast; /* webkit */
image-rendering: -moz-crisp-edges /* Firefox */

http://phrogz.net/tmp/canvas_image_zoom.html 可以使用 canvas 和 getImageData< 提供后备情况/代码>。简而言之：

// Create an offscreen canvas, draw an image to it, and fetch the pixels
var offtx = document.createElement('canvas').getContext('2d');
offtx.drawImage(img1,0,0);
var imgData = offtx.getImageData(0,0,img1.width,img1.height).data;

// Draw the zoomed-up pixels to a different canvas context
for (var x=0;x<img1.width;++x){
  for (var y=0;y<img1.height;++y){
    // Find the starting index in the one-dimensional image data
    var i = (y*img1.width + x)*4;
    var r = imgData[i  ];
    var g = imgData[i+1];
    var b = imgData[i+2];
    var a = imgData[i+3];
    ctx2.fillStyle = "rgba("+r+","+g+","+b+","+(a/255)+")";
    ctx2.fillRect(x*zoom,y*zoom,zoom,zoom);
  }
}

更多：有关图像渲染的 MDN 文档

Answer 2

我不久前使用 ImageData 编写了一个 NN 调整大小脚本（大约第 1794 行）

https ://github.com/arahaya/ImageFilters.js/blob/master/imagefilters.js

您可以在此处查看演示

http://www.arahaya.com/imagefilters/

不幸的是，内置调整大小应该稍微快一些。

Answer 3

您只需设置 context.imageSmoothingEnabled< /a> 到 false。这将使使用 context.drawImage() 绘制的所有内容使用最近邻居调整大小。

// the canvas to resize
const canvas = document.createElement("canvas");

// the canvas to output to
const canvas2 = document.createElement("canvas");
const context2 = canvas2.getContext("2d");

// disable image smoothing
context2.imageSmoothingEnabled = false;

// draw image from the canvas
context2.drawImage(canvas, 0, 0, canvas2.width, canvas2.height);

这比使用有更好的支持图像渲染：像素化。

Answer 4

canvas 元素上的此 CSS 有效：

image-rendering: pixelated;

截至 2021 年 9 月，这适用于 Chrome 93。

Answer 5

我会回应其他人所说的并告诉你这不是一个内置函数。遇到同样的问题后，我在下面做了一个。

它使用 fillRect() 而不是循环遍历每个像素并绘制它。所有内容都带有注释，以帮助您更好地了解其工作原理。

//img is the original image, scale is a multiplier. It returns the resized image.
function Resize_Nearest_Neighbour( img, scale ){
    //make shortcuts for image width and height
    var w = img.width;
    var h = img.height;

    //---------------------------------------------------------------
    //draw the original image to a new canvas
    //---------------------------------------------------------------

    //set up the canvas
    var c = document.createElement("CANVAS");
    var ctx = c.getContext("2d");
    //disable antialiasing on the canvas
    ctx.imageSmoothingEnabled = false;
    //size the canvas to match the input image
    c.width = w;
    c.height = h;
    //draw the input image
    ctx.drawImage( img, 0, 0 );
    //get the input image as image data
    var inputImg = ctx.getImageData(0,0,w,h);
    //get the data array from the canvas image data
    var data = inputImg.data;

    //---------------------------------------------------------------
    //resize the canvas to our bigger output image
    //---------------------------------------------------------------
    c.width = w * scale;
    c.height = h * scale;
    //---------------------------------------------------------------
    //loop through all the data, painting each pixel larger
    //---------------------------------------------------------------
    for ( var i = 0; i < data.length; i+=4 ){

        //find the colour of this particular pixel
        var colour = "#";

        //---------------------------------------------------------------
        //convert the RGB numbers into a hex string. i.e. [255, 10, 100]
        //into "FF0A64"
        //---------------------------------------------------------------
        function _Dex_To_Hex( number ){
            var out = number.toString(16);
            if ( out.length < 2 ){
                out = "0" + out;
            }
            return out;
        }
        for ( var colourIndex = 0; colourIndex < 3; colourIndex++ ){
            colour += _Dex_To_Hex( data[ i+colourIndex ] );
        }
        //set the fill colour
        ctx.fillStyle = colour;

        //---------------------------------------------------------------
        //convert the index in the data array to x and y coordinates
        //---------------------------------------------------------------
        var index = i/4;
        var x = index % w;
        //~~ is a faster way to do 'Math.floor'
        var y = ~~( index / w );
        //---------------------------------------------------------------
        //draw an enlarged rectangle on the enlarged canvas
        //---------------------------------------------------------------
        ctx.fillRect( x*scale, y*scale, scale, scale );
    }

    //get the output image from the canvas
    var output = c.toDataURL("image/png");
    //returns image data that can be plugged into an img tag's src
    return output;
}

下面是它的使用示例。

您的图像将显示在 HTML 中，如下所示：

<img id="pixel-image" src="" data-src="pixel-image.png"/>

data-src 标记包含您要放大的图像的 URL。这是一个自定义数据标签。下面的代码将从数据标记中获取图像 URL，并将其通过调整大小函数，返回一个更大的图像（原始大小的 30 倍），然后将其注入到 的 src 属性中img 标签。

请记住，在包含以下内容之前，请将函数 Resize_Nearest_Neighbour（上面）放入

function Load_Image( element ){
    var source = element.getAttribute("data-src");
    var img = new Image();

    img.addEventListener("load", function(){

        var bigImage = Resize_Nearest_Neighbour( this, 30 );
        element.src = bigImage;

    });

    img.src = source;
}

Load_Image( document.getElementById("pixel-image") );

Answer 6

没有内置的方法。您必须使用 getImageData 自己完成此操作。

Answer 7

基于 Paul Irish 的评论：

function resizeBase64(base64, zoom) {
    return new Promise(function(resolve, reject) {
        var img = document.createElement("img");

        // once image loaded, resize it
        img.onload = function() {
            // get image size
            var imageWidth = img.width;
            var imageHeight = img.height;

            // create and draw image to our first offscreen canvas
            var canvas1 = document.createElement("canvas");
            canvas1.width = imageWidth;
            canvas1.height = imageHeight;
            var ctx1 = canvas1.getContext("2d");
            ctx1.drawImage(this, 0, 0, imageWidth, imageHeight);

            // get pixel data from first canvas
            var imgData = ctx1.getImageData(0, 0, imageWidth, imageHeight).data;

            // create second offscreen canvas at the zoomed size
            var canvas2 = document.createElement("canvas");
            canvas2.width = imageWidth * zoom;
            canvas2.height = imageHeight * zoom;
            var ctx2 = canvas2.getContext("2d");

            // draw the zoomed-up pixels to a the second canvas
            for (var x = 0; x < imageWidth; ++x) {
                for (var y = 0; y < imageHeight; ++y) {
                    // find the starting index in the one-dimensional image data
                    var i = (y * imageWidth + x) * 4;
                    var r = imgData[i];
                    var g = imgData[i + 1];
                    var b = imgData[i + 2];
                    var a = imgData[i + 3];
                    ctx2.fillStyle = "rgba(" + r + "," + g + "," + b + "," + a / 255 + ")";
                    ctx2.fillRect(x * zoom, y * zoom, zoom, zoom);
                }
            }

            // resolve promise with the zoomed base64 image data
            var dataURI = canvas2.toDataURL();
            resolve(dataURI);
        };
        img.onerror = function(error) {
            reject(error);
        };
        // set the img soruce
        img.src = base64;
    });
}

resizeBase64(src, 4).then(function(zoomedSrc) {
    console.log(zoomedSrc);
});

https://jsfiddle.net/djhyquon/69/