我有一些JS用图像进行一些操作。我想要像pixelart一样的图形，所以我不得不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my demo（警告：域名可能会导致某些工作中的问题等）在Firefox中加载时间过长（例如）。 但是当我尝试调整图像大小时，它会被双重重采样。如何在不重新采样的情况下调整图像大小？有没有任何crossbrowser解决方案？
答案 0 :(得分：12)
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提供后备案例。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);
}
}
答案 1 :(得分：3)
我前段时间使用ImageData（第1794行）
编写了一个NN大小调整脚本https://github.com/arahaya/ImageFilters.js/blob/master/imagefilters.js
你可以在这里看到一个演示
不幸的是，内置调整大小应该稍快一些。答案 2 :(得分：0)
没有内置方式。您必须自己使用getImageData。
答案 3 :(得分：0)
我会回应其他人所说的话并告诉你它不是内置功能。在遇到同样的问题之后，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。一切都被评论，以帮助您更好地了解它是如何工作的。
Declare @Text varchar(16) = '123.1234'
SELECT
CAST(@Text AS FLOAT) AS 'Float value'
, CAST(CAST(@Text AS Float) AS NVARCHAR(MAX)) AS 'float'
, CAST(CAST(@Text AS Float(4)) AS NVARCHAR(MAX)) AS 'float with precision'
, CAST(CAST(@Text AS numeric(8,4)) AS NVARCHAR(MAX)) AS 'numeric with precision'
, CAST(CAST(@Text AS decimal(8,4)) AS NVARCHAR(MAX)) AS 'decimal with precision'
下面是一个使用它的例子。
您的图片将显示在HTML中，如下所示：
//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;
}
<img id="pixel-image" src="" data-src="pixel-image.png"/>
标记包含您要放大的图片的网址。这是一个自定义数据标记。下面的代码将从数据标记中获取图像URL并将其放入调整大小函数，返回一个较大的图像（原始大小的30倍），然后将其注入data-src标记的src属性中
在包含以下内容之前，请务必将img（上方）功能放入Resize_Nearest_Neighbour标记。
<script>答案 4 :(得分：-1)
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);
});