Mark Howells-Mead

Forces WordPress to use the ImageMagick image library. This plugin only instructs WordPress to use the ImageMagick library. It doesn’t change how (or when) WordPress generates images, and it doesn’t provide any additional functionality for creating or resizing images.
If you need to know more about ImageMagick, then visit <a href="http://www.imagemagick.org/" rel="nofollow ugc">the official website</a>. Full information about <a href="https://codex.wordpress.org/Post_Thumbnails" rel="nofollow ugc">Post Thumbnails</a> and <a href="https://codex.wordpress.org/Image_Size_and_Quality" rel="nofollow ugc">image size and quality</a> are in the WordPress Codex.

Force use of ImageMagick image library

Forces WordPress to use the ImageMagick image library. This plugin is no longer maintained.

Orangelab

Rickard Westerlind

Dramatically improve the quality of re-sized images by making WordPress use ImageMagick instead of standard GD image library.
Features
<ul>
<li>Preserve embedded color profile in re-sized image</li>
<li>Automatically recognize custom image sizes</li>
<li>Allow regeneration of existing images (optionally for selected image sizes only)</li>
<li>Configure image quality or use dynamically computed default value</li>
<li>Optimize different image sizes for either quality or size</li>
</ul>
Lnguages: English, French, German, Swedish, Turkish
Requires either ImageMagick binary or Imagick PHP module.
<h3>Contribute</h3>
Code repo available on https://github.com/orangelabweb/imagemagick-engine/

ImageMagick Engine

Maybe even better.  It uses ImageMagick Engine that is installed and allows me to easily regenerate all my images.

Works as advertised

The thumbnail regeneration could be a bit faster though. I have used it for longer than I can remember, at least 5 years.

Simple, functional

Improve the quality of re-sized images by replacing standard GD library with ImageMagick.

Force use of ImageMagick image library vs ImageMagick Engine