Post Thumbnails
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Post Thumbnail is a theme feature introduced with Version 2.9. Thumbnail is an image that is chosen as the representative image for Posts, Pages or Custom Post Types. The display of this images is up to the theme. This is especially useful for "magazine-style" themes where each post has an image.
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Enabling Support for Post Thumbnails
Themes have to declare their support for post images before the interface for assigning these images will appear on the Edit Post and Edit Page screens. They do this by putting the following in their functions.php file:
if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'post-thumbnails' );
}
Note: To enable Post Thumbnails only for specific post types see add_theme_support()
Setting a Post Thumbnail
If your theme was successful in adding support for Post Thumbnails the "Featured Image" metabox will be visible on the on the Edit Post and Edit Page screens. If it isn't, make sure "Featured Image" is enabled in the screen options on the top right.
Featured image metabox
After clicking the "Set featured image" link follow the same steps as inserting images in Posts and Pages. But instead of the "Insert into Post" button use the "Use as featured image" link next to it, to set the Post Thumbnail.
Insert image button
Function Reference
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Examples
Default Usage
<?php
if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
the_post_thumbnail();
}
?>
<?php the_content(); ?>
Note: To return the Post Thumbnail for use in your PHP code instead of displaying it, use: get_the_post_thumbnail()
Linking to Post or Larger Image
To link the Post Thumbnail to the Post permalink or a larger image see the examples in the_post_thumbnail()
Thumbnail Sizes
The default image sizes of WordPress are "thumbnail", "medium", "large" and "full" (the image you uploaded). These image sizes can be configured in the WordPress Administration Media panel under Settings > Media. This is how you use these default sizes with the_post_thumbnail():
the_post_thumbnail(); // without parameter -> Thumbnail
the_post_thumbnail('thumbnail'); // Thumbnail (default 150px x 150px max)
the_post_thumbnail('medium'); // Medium resolution (default 300px x 300px max)
the_post_thumbnail('large'); // Large resolution (default 640px x 640px max)
the_post_thumbnail( array(100,100) ); // Other resolutions
Set the Post Thumbnail Size
To be used in the current Theme's functions.php file.
Set the default Post Thumbnail size by resizing the image proportionally (that is, without distorting it):
set_post_thumbnail_size( 50, 50 ); // 50 pixels wide by 50 pixels tall, resize mode
Set the default Post Thumbnail size by cropping the image (either from the sides, or from the top and bottom):
set_post_thumbnail_size( 50, 50, true ); // 50 pixels wide by 50 pixels tall, crop mode
Add New Post Thumbnail Sizes
Example of a new Post Thumbnail size named "category-thumb".
To be used in the current Theme's functions.php file.
add_image_size( 'category-thumb', 300, 9999 ); //300 pixels wide (and unlimited height)
Here is an example of how to use this new Post Thumbnail size in theme template files.
<?php the_post_thumbnail( 'category-thumb' ); ?>
Example of functions.php
if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( 150, 150, true ); // default Post Thumbnail dimensions (cropped)
// additional image sizes
// delete the next line if you do not need additional image sizes
add_image_size( 'category-thumb', 300, 9999 ); //300 pixels wide (and unlimited height)
}
Styling Post Thumbnails
Post Thumbnails are given a class "wp-post-image". They also get a class depending on the size of the thumbnail being displayed You can style the output with these CSS selectors:
img.wp-post-image img.attachment-thumbnail img.attachment-medium img.attachment-large img.attachment-full
You can also give Post Thumbnails their own class.
Display the Post Thumbnail with a class "alignleft":
<?php the_post_thumbnail('thumbnail', array('class' => 'alignleft')); ?>
Source File
External Resources
- Everything you need to know about WordPress 2.9’s post image feature, by JustinTadlock.com
- The Ultimative Guide For the_post_thumbnail In WordPress 2.9, by wpEngineer.com
- New in WordPress 2.9: Post Thumbnail Images, by Mark Jaquith
- Simple WordPress thumbnail function, by Vladimir Prelovac
Related
Post Thumbnails: has_post_thumbnail(), the_post_thumbnail(), get_post_thumbnail_id(), get_the_post_thumbnail(), add_image_size(), set_post_thumbnail_size()
