如何按比例调整图像大小/保持宽高比？

我的图片尺寸会很大，我想使用jQuery缩小图片，同时保持比例不变，即长宽比相同。

有人可以指出一些代码或解释其逻辑吗？

看看来自http://ericjuden.com/2009/07/jquery-image-resize/的这段代码

$(document).ready(function() {
    $('.story-small img').each(function() {
        var maxWidth = 100; // Max width for the image
        var maxHeight = 100;    // Max height for the image
        var ratio = 0;  // Used for aspect ratio
        var width = $(this).width();    // Current image width
        var height = $(this).height();  // Current image height

        // Check if the current width is larger than the max
        if(width > maxWidth){
            ratio = maxWidth / width;   // get ratio for scaling image
            $(this).css("width", maxWidth); // Set new width
            $(this).css("height", height * ratio);  // Scale height based on ratio
            height = height * ratio;    // Reset height to match scaled image
            width = width * ratio;    // Reset width to match scaled image
        }

        // Check if current height is larger than max
        if(height > maxHeight){
            ratio = maxHeight / height; // get ratio for scaling image
            $(this).css("height", maxHeight);   // Set new height
            $(this).css("width", width * ratio);    // Scale width based on ratio
            width = width * ratio;    // Reset width to match scaled image
            height = height * ratio;    // Reset height to match scaled image
        }
    });
});

我认为这是一种非常酷的方法：

 /**
  * Conserve aspect ratio of the original region. Useful when shrinking/enlarging
  * images to fit into a certain area.
  *
  * @param {Number} srcWidth width of source image
  * @param {Number} srcHeight height of source image
  * @param {Number} maxWidth maximum available width
  * @param {Number} maxHeight maximum available height
  * @return {Object} { width, height }
  */
function calculateAspectRatioFit(srcWidth, srcHeight, maxWidth, maxHeight) {

    var ratio = Math.min(maxWidth / srcWidth, maxHeight / srcHeight);

    return { width: srcWidth*ratio, height: srcHeight*ratio };
 }

如果我正确理解了这个问题，那么您甚至不需要jQuery。仅使用CSS即可在客户端上按比例缩小图像：只需将其max-width和设置为max-height即可100%。

<div style="height: 100px">
<img src="http://www.getdigital.de/images/produkte/t4/t4_css_sucks2.jpg"
    style="max-height: 100%; max-width: 100%">
</div>​

这是小提琴：http : //jsfiddle.net/9EQ5c/

为了确定纵横比，您需要有一个目标比例。

function getHeight(length, ratio) {
  var height = ((length)/(Math.sqrt((Math.pow(ratio, 2)+1))));
  return Math.round(height);
}

function getWidth(length, ratio) {
  var width = ((length)/(Math.sqrt((1)/(Math.pow(ratio, 2)+1))));
  return Math.round(width);
}

在此示例中，我使用16:10了典型的监视器宽高比。

var ratio = (16/10);
var height = getHeight(300,ratio);
var width = getWidth(height,ratio);

console.log(height);
console.log(width);

从上面的结果将是147和300

其实我刚遇到这个问题，我发现的解决方案很奇怪又奇怪

$("#someimage").css({height:<some new height>})

奇迹般地将图像调整为新的高度并保持相同的比例！

这个问题有4个参数

1. 当前图像宽度iX
2. 当前图像高度iY
3. 目标视口宽度cX
4. 目标视口高度cY

并且有3个不同的条件参数

1. cX> cY吗？
2. iX> cX？
3. iY> cY？

解

1. 找到目标视口F的较小一侧
2. 查找当前查看端口L的较大侧
3. 找出两个F / L的因子=因子
4. 将当前端口的两侧乘以系数，即fX = iX *系数；fY = iY *因子

这就是您需要做的。

//Pseudo code


iX;//current width of image in the client
iY;//current height of image in the client
cX;//configured width
cY;//configured height
fX;//final width
fY;//final height

1. check if iX,iY,cX,cY values are >0 and all values are not empty or not junk

2. lE = iX > iY ? iX: iY; //long edge

3. if ( cX < cY )
   then
4.      factor = cX/lE;     
   else
5.      factor = cY/lE;

6. fX = iX * factor ; fY = iY * factor ; 

这是一个成熟的论坛，我没有为您提供代码:)

有<img src="/path/to/pic.jpg" style="max-width:XXXpx; max-height:YYYpx;" >帮助吗？

浏览器会注意保持长宽比不变。

也就是说max-width，当图像宽度大于高度时会踢进去，并且其高度将按比例计算。max-height当高度大于宽度时，同样会生效。

您不需要任何jQuery或javascript。

受ie7 +和其他浏览器（http://caniuse.com/minmaxwh）的支持。

这应该适用于所有可能比例的图像

$(document).ready(function() {
    $('.list img').each(function() {
        var maxWidth = 100;
        var maxHeight = 100;
        var width = $(this).width();
        var height = $(this).height();
        var ratioW = maxWidth / width;  // Width ratio
        var ratioH = maxHeight / height;  // Height ratio

        // If height ratio is bigger then we need to scale height
        if(ratioH > ratioW){
            $(this).css("width", maxWidth);
            $(this).css("height", height * ratioW);  // Scale height according to width ratio
        }
        else{ // otherwise we scale width
            $(this).css("height", maxHeight);
            $(this).css("width", height * ratioH);  // according to height ratio
        }
    });
});

这是对Mehdiway答案的更正。新的宽度和/或高度未设置为最大值。以下是一个很好的测试用例（1768 x 1075像素）：http : //spacecoastsports.com/wp-content/uploads/2014/06/sportsballs1.png。（由于缺乏声誉，我无法在上面对此发表评论。）

  // Make sure image doesn't exceed 100x100 pixels
  // note: takes jQuery img object not HTML: so width is a function
  // not a property.
  function resize_image (image) {
      var maxWidth = 100;           // Max width for the image
      var maxHeight = 100;          // Max height for the image
      var ratio = 0;                // Used for aspect ratio

      // Get current dimensions
      var width = image.width()
      var height = image.height(); 
      console.log("dimensions: " + width + "x" + height);

      // If the current width is larger than the max, scale height
      // to ratio of max width to current and then set width to max.
      if (width > maxWidth) {
          console.log("Shrinking width (and scaling height)")
          ratio = maxWidth / width;
          height = height * ratio;
          width = maxWidth;
          image.css("width", width);
          image.css("height", height);
          console.log("new dimensions: " + width + "x" + height);
      }

      // If the current height is larger than the max, scale width
      // to ratio of max height to current and then set height to max.
      if (height > maxHeight) {
          console.log("Shrinking height (and scaling width)")
          ratio = maxHeight / height;
          width = width * ratio;
          height = maxHeight;
          image.css("width", width);
          image.css("height", height);
          console.log("new dimensions: " + width + "x" + height);
      }
  }

$('#productThumb img').each(function() {
    var maxWidth = 140; // Max width for the image
    var maxHeight = 140;    // Max height for the image
    var ratio = 0;  // Used for aspect ratio
    var width = $(this).width();    // Current image width
    var height = $(this).height();  // Current image height
    // Check if the current width is larger than the max
    if(width > height){
        height = ( height / width ) * maxHeight;

    } else if(height > width){
        maxWidth = (width/height)* maxWidth;
    }
    $(this).css("width", maxWidth); // Set new width
    $(this).css("height", maxHeight);  // Scale height based on ratio
});

如果图像是成比例的，则此代码将用图像填充包装器。如果图像不成比例，则多余的宽度/高度将被裁剪。

    <script type="text/javascript">
        $(function(){
            $('#slider img').each(function(){
                var ReqWidth = 1000; // Max width for the image
                var ReqHeight = 300; // Max height for the image
                var width = $(this).width(); // Current image width
                var height = $(this).height(); // Current image height
                // Check if the current width is larger than the max
                if (width > height && height < ReqHeight) {

                    $(this).css("min-height", ReqHeight); // Set new height
                }
                else 
                    if (width > height && width < ReqWidth) {

                        $(this).css("min-width", ReqWidth); // Set new width
                    }
                    else 
                        if (width > height && width > ReqWidth) {

                            $(this).css("max-width", ReqWidth); // Set new width
                        }
                        else 
                            (height > width && width < ReqWidth)
                {

                    $(this).css("min-width", ReqWidth); // Set new width
                }
            });
        });
    </script>

没有额外的临时变量或括号。

    var width= $(this).width(), height= $(this).height()
      , maxWidth=100, maxHeight= 100;

    if(width > maxWidth){
      height = Math.floor( maxWidth * height / width );
      width = maxWidth
      }
    if(height > maxHeight){
      width = Math.floor( maxHeight * width / height );
      height = maxHeight;
      }

注意：如果width和height属性不适合图像，但他们不知道JS，搜索引擎将不喜欢它。

经过一番反复尝试后，我得出了以下解决方案：

function center(img) {
    var div = img.parentNode;
    var divW = parseInt(div.style.width);
    var divH = parseInt(div.style.height);
    var srcW = img.width;
    var srcH = img.height;
    var ratio = Math.min(divW/srcW, divH/srcH);
    var newW = img.width * ratio;
    var newH = img.height * ratio;
    img.style.width  = newW + "px";
    img.style.height = newH + "px";
    img.style.marginTop = (divH-newH)/2 + "px";
    img.style.marginLeft = (divW-newW)/2 + "px";
}

可以使用CSS来调整尺寸（保持纵横比）。这是由Dan Dascalescu的帖子启发的进一步简化的答案。

http://jsbin.com/viqare

img{
     max-width:200px;
 /*Or define max-height*/
  }

<img src="http://e1.365dm.com/13/07/4-3/20/alastair-cook-ashes-profile_2967773.jpg"  alt="Alastair Cook" />

<img src="http://e1.365dm.com/13/07/4-3/20/usman-khawaja-australia-profile_2974601.jpg" alt="Usman Khawaja"/>

2个步骤：

步骤1）计算Image的原始宽度/原始高度的比率。

步骤2）将original_width / original_height比值乘以新的所需高度，以获得与新高度相对应的新宽度。

CSS可以解决这个问题。

.image{
 max-width:*px;
}

这对我来说完全适用于可拖动的项目-AspectRatio：true

.appendTo(divwrapper).resizable({
    aspectRatio: true,
    handles: 'se',
    stop: resizestop 
})