Caution

CSS now has broad support to achieve the same thing as this library using object-fit: cover; and object-position: var(--x, 50%) var(--y, 50%); where x and y can go from 0-100%.

See example here

image-focus 📷

A dependency free utility for cropping images based on a focus point ~2.13kB gzipped

Demo

Check out the demo and then play with editing it

Docs

Docs generated by typedoc

Usage

Focus Coordinates range between -1 and 1 for both x and y axes. The FocusPicker class will help enable users to select the focus point to be used with an image.

FocusedImage

There are two ways to supply the coordinates when initializing the FocusedImage class

Data Tags

<div class="focused-image-container">
  <img
    class="focused-image"
    src="https://picsum.photos/2400/1400"
    data-focus-x="0.34"
    data-focus-y="-0.21"
  />
</div>

import { FocusedImage } from 'image-focus';

const img = document.querySelector('.focused-image') as HTMLImageElement;
const focusedImage = new FocusedImage(img);

Using focus Option

<div class="focused-image-container">
  <img class="focused-image" src="https://picsum.photos/2400/1400" />
</div>

import { FocusedImage } from 'image-focus';

const img = document.querySelector('.focused-image') as HTMLImageElement;
const focusedImage = new FocusedImage(img, {
  focus: {
    x: 0.34,
    y: -0.21,
  },
});

FocusPicker

Provide an onChange callback that will receive a Focus object that has x and y properties for the newly selected coordinates. Optionally supply a focus to initialize with, or a retina src to use instead of the default white ring SVG.

import { FocusedImage, FocusPicker } from 'image-focus';

const imgEl = document.getElementById('focused-image') as HTMLImageElement;
const focusedImage = new FocusedImage(imgEl);

const focusPickerEl = document.getElementById(
  'focus-picker-img'
) as HTMLImageElement;
const focusPicker = new FocusPicker(focusPickerEl, {
  onChange: focus => focusedImage.setFocus(focus),
  focus: startingFocus,
});

What's going on?

The <img/> element is being set to position: absolute; and having its top and left properties adjusted based on some calculations using the image and parent containers' aspect ratios and dimensions. The <img/>'s parent container gets set to position: relative; and overflow: hidden; to create the effect. There are a few other inline styles that get applied, so if anything appears to be behaving unexpectedly, be sure to check that the inline styles on both the <img/> and its parent aren't being overridden by CSS on your page (especially from rules using !important).

Additionally, because the FocusedImage is positioned absolutely so it can shift as needed, its container needs to manage its own height and width. If you aren't seeing an image appear at all, it is likely that the parent div's height is fully collapsed.

What if I'm not using npm and a build process?

That's okay! unpkg has you covered. Just add this script tag to your page and the image-focus module is exposed in the global namespace under window.imageFocus.

<script src="https://unpkg.com/image-focus@1.0.2"></script>

Then in some script that loads after the above script tag:

var imgEl = document.querySelector('img.focused-image');
var focusedImage = new imageFocus.FocusedImage(imgEl, { x: 0.25, y: -0.3 });

Attributions

This project was largely inspired by and adapted from jquery-focuspoint by jonom and used typescript-library-starter to scaffold the build process.