jQuery resize to aspect ratio

Question

How would I resize a image in jQuery to a consistent aspect ratio. For example setting maximum height and have the width resize correctly. Thanks.

Answer 1

Here's a useful function that might do what you want:

jQuery.fn.fitToParent = function()
{
    this.each(function()
    {
        var width  = $(this).width();
        var height = $(this).height();
        var parentWidth  = $(this).parent().width();
        var parentHeight = $(this).parent().height();

        if(width/parentWidth < height/parentHeight) {
            newWidth  = parentWidth;
            newHeight = newWidth/width*height;
        }
        else {
            newHeight = parentHeight;
            newWidth  = newHeight/height*width;
        }
        var margin_top  = (parentHeight - newHeight) / 2;
        var margin_left = (parentWidth  - newWidth ) / 2;

        $(this).css({'margin-top' :margin_top  + 'px',
                     'margin-left':margin_left + 'px',
                     'height'     :newHeight   + 'px',
                     'width'      :newWidth    + 'px'});
    });
};

Basically, it grabs an element, centers it within the parent, then stretches it to fit such that none of the parent's background is visible, while maintaining the aspect ratio.

Then again, this might not be what you want to do.

Answer 2

You could calculate this manually,

i.e.:

function GetWidth(newHeight,orginalWidth,originalHeight)
{
if(currentHeight == 0)return newHeight;
var aspectRatio = currentWidth / currentHeight;
return newHeight * aspectRatio;
}

Make sure you use the ORIGINAL values for the image otherwise it will degrade over time.

EDIT: example jQuery version (not tested)

jQuery.fn.resizeHeightMaintainRatio = function(newHeight){
    var aspectRatio = $(this).data('aspectRatio');
    if (aspectRatio == undefined) {
        aspectRatio = $(this).width() / $(this).height();
        $(this).data('aspectRatio', aspectRatio);
    }
    $(this).height(newHeight); 
    $(this).width(parseInt(newHeight * aspectRatio));
}

Answer 3

Use JQueryUI Resizeable

$("#some_image").resizable({ aspectRatio:true, maxHeight:300 });

aspectRatio: true -> maintain original aspect ratio

Answer 4

There's no accounting for the amount of copy and pasters out there eh! I also wanted to know this and all I saw were endless examples of scaling width OR height.. who would want the other overflowing?!

• Resize width AND height without the need for a loop
• Doesn't exceed the images original dimensions
• Uses maths that works properly i.e width/aspect for height, and height*aspect for width so images are actually scaled properly up and down :/

Should be straight forward enough to convert to javascript or other languages

//////////////

private void ResizeImage(Image img, double maxWidth, double maxHeight)
{
    double srcWidth = img.Width;
    double srcHeight = img.Height;

    double resizeWidth = srcWidth;
    double resizeHeight = srcHeight;

    double aspect = resizeWidth / resizeHeight;

    if (resizeWidth > maxWidth)
    {
        resizeWidth = maxWidth;
        resizeHeight = resizeWidth / aspect;
    }
    if (resizeHeight > maxHeight)
    {
        aspect = resizeWidth / resizeHeight;
        resizeHeight = maxHeight;
        resizeWidth = resizeHeight * aspect;
    }

    img.Width = resizeWidth;
    img.Height = resizeHeight;
}

Answer 5

This is a good solution if you need perfect height and width aspect ratio after crop it will give perfect crop ratio

getPerfectRatio(img,widthRatio,heightRatio){

  if(widthRatio < heightRatio){
    var height = img.scalingHeight - (img.scalingHeight % heightRatio);
    var finalHeight = height
    var finalWidth = widthRatio * (height/heightRatio);

    img.cropHeight = finalHeight;
    img.cropWidth = finalWidth
  }
  if(heightRatio < widthRatio){;
    var width = img.scalingWidth - (img.scalingWidth % widthRatio);
    var finalWidth = width;
    var finalHeight  = heightRatio * (width/widthRatio);
    img.cropHeight = finalHeight;
    img.cropWidth = finalWidth
  }

  return img
  
}