我正在尝试使用画布调整某些图像的大小,但是我对如何使其平滑一无所知。在photoshop,浏览器等上。它们使用几种算法(例如,双三次,双线性),但我不知道这些算法是否内置在画布中。
这是我的小提琴:http://jsfiddle.net/EWupT/
var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
canvas.width=300
canvas.height=234
ctx.drawImage(img, 0, 0, 300, 234);
document.body.appendChild(canvas);
第一个是正常尺寸的图像标签,第二个是画布。请注意,画布如何不那么光滑。如何获得“平滑度”?
您可以使用降级以获得更好的结果。调整图像大小时,大多数浏览器似乎为use linear interpolation rather than bi-cubic。
(<< [Update已在规范中添加了quality属性,imageSmoothingQuality
仅在Chrome中可用。]
[双线性使用2x2像素进行插值,而双三次使用4x4,因此,通过逐步进行操作,您可以在使用双线性插值时获得接近双三次的结果,如在所得图像中看到的。
imageSmoothingQuality
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var img = new Image();
img.onload = function () {
// set size proportional to image
canvas.height = canvas.width * (img.height / img.width);
// step 1 - resize to 50%
var oc = document.createElement('canvas'),
octx = oc.getContext('2d');
oc.width = img.width * 0.5;
oc.height = img.height * 0.5;
octx.drawImage(img, 0, 0, oc.width, oc.height);
// step 2
octx.drawImage(oc, 0, 0, oc.width * 0.5, oc.height * 0.5);
// step 3, resize to final size
ctx.drawImage(oc, 0, 0, oc.width * 0.5, oc.height * 0.5,
0, 0, canvas.width, canvas.height);
}
img.src = "//i.imgur.com/SHo6Fub.jpg";
根据调整大小的剧烈程度,如果差异较小,可以跳过第2步。在演示中,您可以看到新结果现在与图像元素非常相似。
<img src="//i.imgur.com/SHo6Fub.jpg" width="300" height="234">
<canvas id="canvas" width=300></canvas>
该服务包括两个解决方案,因为它们都有各自的优缺点。 lanczos卷积方法的质量较高,但代价是速度较慢,而逐步缩小的方法则可以产生合理的抗锯齿结果,并且速度明显更快。
示例用法:
https://gist.github.com/transitive-bullshit/37bac5e741eaec60e983
angular.module('demo').controller('ExampleCtrl', function (imageService) {
// EXAMPLE USAGE
// NOTE: it's bad practice to access the DOM inside a controller,
// but this is just to show the example usage.
// resize by lanczos-sinc filter
imageService.resize($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
// resize by stepping down image size in increments of 2x
imageService.resizeStep($('#myimg')[0], 256, 256)
.then(function (resizedImage) {
// do something with resized image
})
})
根本不正确(它仅在最后一步中使用原始图像)我用性能比较写了自己的小提琴:基本上是:
img.onload = function() {
var canvas = document.createElement('canvas'),
ctx = canvas.getContext("2d"),
oc = document.createElement('canvas'),
octx = oc.getContext('2d');
canvas.width = width; // destination canvas size
canvas.height = canvas.width * img.height / img.width;
var cur = {
width: Math.floor(img.width * 0.5),
height: Math.floor(img.height * 0.5)
}
oc.width = cur.width;
oc.height = cur.height;
octx.drawImage(img, 0, 0, cur.width, cur.height);
while (cur.width * 0.5 > width) {
cur = {
width: Math.floor(cur.width * 0.5),
height: Math.floor(cur.height * 0.5)
};
octx.drawImage(oc, 0, 0, cur.width * 2, cur.height * 2, 0, 0, cur.width, cur.height);
}
ctx.drawImage(oc, 0, 0, cur.width, cur.height, 0, 0, canvas.width, canvas.height);
}
您可以在浏览器中包含的文件。结果将看起来像photoshop或图像魔术,保留所有颜色数据,平均像素,而不是获取附近的像素并丢弃其他像素。它不使用公式来猜测平均值,而是使用精确的平均值。
https://github.com/danschumann/limby-resize/blob/master/lib/canvas_resize.js
更新JSFIDDLE演示
这里是我的var oc = document.createElement('canvas'), octx = oc.getContext('2d'); oc.width = img.width; oc.height = img.height; octx.drawImage(img, 0, 0); while (oc.width * 0.5 > width) { oc.width *= 0.5; oc.height *= 0.5; octx.drawImage(oc, 0, 0, oc.width, oc.height); } oc.width = width; oc.height = oc.width * img.height / img.width; octx.drawImage(img, 0, 0, oc.width, oc.height);
由于我不喜欢堆栈溢出的“复制-粘贴”,我希望开发人员了解他们将代码推送到软件中,希望您会发现以下有用。
DEMO:使用JS和HTML Canvas演示小提琴手调整图像大小。
您可能会找到3种不同的方法来进行此大小调整,这将有助于您了解代码的工作方式以及原因。可以在GitHub项目中找到您可能想在代码中使用的全部演示代码和TypeScript方法的完整代码。
https://jsfiddle.net/1b68eLdr/93089/
这是最终代码:
export class ImageTools {
base64ResizedImage: string = null;
constructor() {
}
ResizeImage(base64image: string, width: number = 1080, height: number = 1080) {
let img = new Image();
img.src = base64image;
img.onload = () => {
// Check if the image require resize at all
if(img.height <= height && img.width <= width) {
this.base64ResizedImage = base64image;
// TODO: Call method to do something with the resize image
}
else {
// Make sure the width and height preserve the original aspect ratio and adjust if needed
if(img.height > img.width) {
width = Math.floor(height * (img.width / img.height));
}
else {
height = Math.floor(width * (img.height / img.width));
}
let resizingCanvas: HTMLCanvasElement = document.createElement('canvas');
let resizingCanvasContext = resizingCanvas.getContext("2d");
// Start with original image size
resizingCanvas.width = img.width;
resizingCanvas.height = img.height;
// Draw the original image on the (temp) resizing canvas
resizingCanvasContext.drawImage(img, 0, 0, resizingCanvas.width, resizingCanvas.height);
let curImageDimensions = {
width: Math.floor(img.width),
height: Math.floor(img.height)
};
let halfImageDimensions = {
width: null,
height: null
};
// Quickly reduce the dize by 50% each time in few iterations until the size is less then
// 2x time the target size - the motivation for it, is to reduce the aliasing that would have been
// created with direct reduction of very big image to small image
while (curImageDimensions.width * 0.5 > width) {
// Reduce the resizing canvas by half and refresh the image
halfImageDimensions.width = Math.floor(curImageDimensions.width * 0.5);
halfImageDimensions.height = Math.floor(curImageDimensions.height * 0.5);
resizingCanvasContext.drawImage(resizingCanvas, 0, 0, curImageDimensions.width, curImageDimensions.height,
0, 0, halfImageDimensions.width, halfImageDimensions.height);
curImageDimensions.width = halfImageDimensions.width;
curImageDimensions.height = halfImageDimensions.height;
}
// Now do final resize for the resizingCanvas to meet the dimension requirments
// directly to the output canvas, that will output the final image
let outputCanvas: HTMLCanvasElement = document.createElement('canvas');
let outputCanvasContext = outputCanvas.getContext("2d");
outputCanvas.width = width;
outputCanvas.height = height;
outputCanvasContext.drawImage(resizingCanvas, 0, 0, curImageDimensions.width, curImageDimensions.height,
0, 0, width, height);
// output the canvas pixels as an image. params: format, quality
this.base64ResizedImage = outputCanvas.toDataURL('image/jpeg', 0.85);
// TODO: Call method to do something with the resize image
}
};
}}
。您也可以从最终图像中获取斑点以发送它。