jQuery plugin like Tone Curve on Photoshop or GIMP. See Official page for more information.
Create HTML and open in your browser.
<div class="iocurve" style="width:300px"></div>
<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/cmiz/jquery.iocurve@0.0.6/dist/jquery.iocurve.min.js"></script>
<script>
$('.iocurve').iocurve();
</script>