One of the foundational principles of a responsive site like ProPhoto is to serve differently sized versions of the same image at different viewport widths. Choose between two image libraries for this downsizing process in “ProPhoto > Settings > Site Settings > Misc > Individual image downsizing.”
There is module called “GD” that is (with very few exceptions) installed and available on any server that is compatible with ProPhoto. You don’t have to do anything to activate it and ProPhoto uses it by default to downsize, crop, and watermark your images. It is very useful but has some limitations, the most notable of which is that operations performed on images using GD don’t retain an image’s color profile. Sometimes you’ll notice that colors within an image downsized by ProPhoto will look slightly different when compared to the original.
The good news is that there is a newer module called “ImageMagick” that is faster, provides better image quality, retains color profiles, and offers some additional features. Web-host support for this module isn’t as widespread as for GD, but many good hosts make it available. To see if ImageMagick is active on your server, log into your ProPhoto admin area and go to “ProPhoto > Settings > Site Settings > Misc > Individual Image Downsizing.” If you see the following option in that area, then ImageMagick is installed and active on your server. Simply select the ImageMagick option and skip ahead to the “ImageMagick Options” area below.
If you see a message indicating that ImageMagick isn’t active on your server, it may still be available.
It’s possible that you can enable it in a PHP configuration area in your hosting control panel. Or, if you need help, contact your web host support and tell them something like this:
Hi, I have a website which uses the WordPress platform, and it processes my photos to make thumbnails and other smaller copies of my images. I would like my website to use the “ImageMagick” tool, but my WordPress theme developer says that it cannot access ImageMagick on my server. Can you please check to make sure my server has the ImageMagick software installed, and also that my server PHP environment has the Imagick 3.4.3 PECL module enabled? Thank you!
Hopefully they will be able to enable this for your web server, but your site will still use the GD library to downsize images if they cannot.
Any time you resize an image you will lose some quality and sharpness, even if just a tiny bit. ImageMagick does a better job than GD, but there is still some loss in quality. You can counter this by applying a sharpening effect to any images that are downsized. A value of zero doesn’t apply any sharpening, while ten applies the maximum amount of sharpening.