Customizing RSS feeds in WordPress: Increasing image sizes

by Ryan Tvenge

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This morning just like any other, was going through my RSS feeds looking at the latest news. I had notices on sites like MacStories that they have really nice, big images in their content. I then got pulled into a rat hole of research trying to get this working on this site¹.

When you insert an image in a WordPress post, you can choose a “smaller than original” image. This is great for your website, not serving the user too big of an image. But RSS readers are a little different. There isn’t nearly as much overhead to the content payload. So serving up the full image might be ok.

function rss_feed_filter($query) {
	if ($query->is_feed) {
		add_filter('the_content', 'rss_feed_content_filter');
		}
	return $query;
}
add_filter('pre_get_posts','rss_feed_filter');

function rss_feed_content_filter($content) {

  // Nasty RegEx to get attributes and replace in $content.
  $content = preg_replace('/<img.*src="(.*)\-[0-9]*x[0-9]*(.[a-zA-Z]{3,4})".*alt="(.*)"[ \/]?[^\>]*>/', '<img src="${1}${2}" alt="${3}" \>', $content);

  return $content;
}

Thanks to Michael Martin for this post on filtering RSS feed content.

We are doing a few things:

1. Getting into the RSS Feed content to filter it.
2. Doing a preg_replace() to find the src and alt attributes.
3. With finding the src attribute, we are only extracting the original file name and extension. We want to strip out the -200x200 in order to get the original image size.
4. Rewriting the <img> with only the attributes we want.