我使用html5画布元素在浏览器中调整图像的大小。事实证明,质量非常低。我发现了这一点:Disable Interpolation when Scaling a ,但它对提高质量没有帮助。
下面是我的css和js代码,以及用Photoshop缩放和在canvas API中缩放的图像。
在浏览器中缩放图像时,如何获得最佳质量?
注意:我希望将大图像缩小为小图像,在画布中修改颜色,并将结果从画布发送到服务器。
CSS:
canvas, img {
image-rendering: optimizeQuality;
image-rendering: -moz-crisp-edges;
image-rendering: -webkit-optimize-contrast;
image-rendering: optimize-contrast;
-ms-interpolation-mode: nearest-neighbor;
}
JS:
var $img = $('<img>');
var $originalCanvas = $('<canvas>');
$img.load(function() {
var originalContext = $originalCanvas[0].getContext('2d');
originalContext.imageSmoothingEnabled = false;
originalContext.webkitImageSmoothingEnabled = false;
originalContext.mozImageSmoothingEnabled = false;
originalContext.drawImage(this, 0, 0, 379, 500);
});
使用photoshop调整图像大小:
在画布上调整图像大小:
编辑:
我尝试按照下面的建议在多个步骤中进行缩容:
Resizing an image in an HTML5 canvas和Html5 canvas drawImage: how to apply antialiasing
这是我用过的函数:
function resizeCanvasImage(img, canvas, maxWidth, maxHeight) {
var imgWidth = img.width,
imgHeight = img.height;
var ratio = 1, ratio1 = 1, ratio2 = 1;
ratio1 = maxWidth / imgWidth;
ratio2 = maxHeight / imgHeight;
// Use the smallest ratio that the image best fit into the maxWidth x maxHeight box.
if (ratio1 < ratio2) {
ratio = ratio1;
}
else {
ratio = ratio2;
}
var canvasContext = canvas.getContext("2d");
var canvasCopy = document.createElement("canvas");
var copyContext = canvasCopy.getContext("2d");
var canvasCopy2 = document.createElement("canvas");
var copyContext2 = canvasCopy2.getContext("2d");
canvasCopy.width = imgWidth;
canvasCopy.height = imgHeight;
copyContext.drawImage(img, 0, 0);
// init
canvasCopy2.width = imgWidth;
canvasCopy2.height = imgHeight;
copyContext2.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvasCopy2.width, canvasCopy2.height);
var rounds = 2;
var roundRatio = ratio * rounds;
for (var i = 1; i <= rounds; i++) {
console.log("Step: "+i);
// tmp
canvasCopy.width = imgWidth * roundRatio / i;
canvasCopy.height = imgHeight * roundRatio / i;
copyContext.drawImage(canvasCopy2, 0, 0, canvasCopy2.width, canvasCopy2.height, 0, 0, canvasCopy.width, canvasCopy.height);
// copy back
canvasCopy2.width = imgWidth * roundRatio / i;
canvasCopy2.height = imgHeight * roundRatio / i;
copyContext2.drawImage(canvasCopy, 0, 0, canvasCopy.width, canvasCopy.height, 0, 0, canvasCopy2.width, canvasCopy2.height);
} // end for
// copy back to canvas
canvas.width = imgWidth * roundRatio / rounds;
canvas.height = imgHeight * roundRatio / rounds;
canvasContext.drawImage(canvasCopy2, 0, 0, canvasCopy2.width, canvasCopy2.height, 0, 0, canvas.width, canvas.height);
}
下面是如果我使用2级缩容的结果:
下面是如果我使用3级缩容的结果:
下面是如果我使用4级缩容的结果:
下面是如果我使用20级缩容的结果:
注意:事实证明,从1步到2步,图像质量有了很大的提高,但添加到该过程中的步骤越多,图像就变得越模糊。
添加的步骤越多,图像越模糊,有没有办法解决这个问题?
编辑2013-10-04:我尝试了GameAlchemist的算法。这是与Photoshop进行比较的结果。
PhotoShop图像:
GameAlchemist的算法:
https://stackoverflow.com/questions/18922880
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