Is it possible to use percentage values for width and height in image transforms? I'm working on creating an image transform to handle retina images. I upload the 2x assets and need an image transform to create my images at 50% their original size. Since images on the site can be varying widths and heights I am currently forced to create a new image transform for each image ratio. Percentage values would cut this down to a single image transform for everything.
It’s possible to do this from your templates:

{% for image in entry.myAssetsField %}

    {% set half = {
        width: (image.width/2)|round,
        height: (image.height/2)|round
    } %}

    {% set halfUrl = image.getUrl(half) %}

    &lt;img src="{{ halfUrl }}" srcset="{{ image.url }} 2x" width="{{ half.width }}" height="{{ half.height }}"&gt;

{% endfor %}