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Function Reference/add image size

Contents

Description

Registers a new image size. This means that WordPress will create a copy of the Featured Image (formerly known as post thumbnail) with the specified dimensions when you upload a new image.

Note: To enable featured images, or post thumbnails, the current theme must include add_theme_support( 'post-thumbnails' ); in its functions.php file. See also Post Thumbnails.

Usage

<?php add_image_size$name$width$height$crop ); ?>

Parameters

$name
(string) (required) The new image size name.
Default: None
$width
(int) (optional) The post thumbnail width in pixels.
Default: 0
$height
(int) (optional) The post thumbnail height in pixels.
Default: 0
$crop
(boolean/array) (optional) Whether to crop images to specified height and width or resize:
  • false - Soft proportional crop mode.
  • true - Hard crop mode.
  • array - Can specify positioning of the crop area.
Default: false

Reserved Image Size Names

thumb, thumbnail, medium, large, post-thumbnail

The names "thumb" & "thumbnail" are just alias, so exactly the same.

For a detailed explanation and "why", read further inside the image_downsize() article.

However, if needed, you can always set the options yourself:

update_option('thumbnail_size_w', 160);
update_option('thumbnail_size_h', 160);
update_option('thumbnail_crop', 1);

Examples

A theme's functions.php file.

if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support( 'post-thumbnails' );
        set_post_thumbnail_size( 150, 150 ); // default Post Thumbnail dimensions   
}

if ( function_exists( 'add_image_size' ) ) { 
	add_image_size( 'category-thumb', 300 ); //300 pixels wide (and unlimited height)
	add_image_size( 'homepage-thumb', 220, 180, true ); //(cropped)
}

Crop Mode

Set the image size by resizing the image proportionally (that is, without distorting it):

add_image_size( 'homepage-thumb', 220, 180 ); // 220 pixels wide by 180 pixels tall, soft proportional crop mode

Set the image size by cropping the image (either from the sides, or from the top and bottom):

add_image_size( 'homepage-thumb', 220, 180, true ); // 220 pixels wide by 180 pixels tall, hard crop mode

Using the New Image Sizes

Now that you've defined some custom image sizes, there are a variety of ways that you can use them.

For Featured Images

To use your custom image sizes for a post's featured image, you can use the_post_thumbnail() in the appropriate theme template file...

<?php 
    if ( has_post_thumbnail() ) { 
        the_post_thumbnail( 'your-custom-size' ); 
    } 
?>

For Media Library Images (Admin)

You can also make your custom sizes selectable from your WordPress admin. To do so, you have to use the image_size_names_choose hook to assign them a normal, human-readable name...

add_filter( 'image_size_names_choose', 'my_custom_sizes' );

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'your-custom-size' => __('Your Custom Size Name'),
    ) );
}

For General Media (PHP/Templates)

You can output images (by size) directly from the WordPress Media Library using PHP as well. To do this, simply use wp_get_attachment_image()...

// Assuming your Media Library image has a post id of 42...
<?php echo wp_get_attachment_image( 42, 'your-custom-size' ) ?>

Note: If you just want the image URL instead of a pre-built <img> tag, you can use wp_get_attachment_image_src() instead.

Notes

Using the 'false' setting will fail to produce a new image in the upload directory if one of the image dimensions of the uploaded image are equal to the new image size.

Change Log

Source File

add_image_size() is located in wp-includes/media.php.

Resources

Regenerate Thumbnails - This plugin regenerate the thumbnails for your image attachments. This is very handy if you've changed any of your thumbnail dimensions (via Settings -> Media) after previously uploading images or have changed to a theme with different featured post image dimensions.

AJAX thumbnail rebuild - This plugin allows you to re-build the post thumbnails. Useful if you use add_image_size() after already having uploaded post thumbnails. (This plugin is slow, but never has out of memory errors).

Simple Image Sizes - This plugin allows you create new sizes of thumbnails directly from the "Media" panel. It allows you to regenerate the thumbnails too. The plugin adds the thumbnails to your post sizes and you can add them directly on your posts. You can choose the sizes you wanted to regenerate and the posts types too.

Related

Post Thumbnails: has_post_thumbnail(), the_post_thumbnail(), get_post_thumbnail_id(), get_the_post_thumbnail(), add_image_size(), set_post_thumbnail_size()

See also index of Function Reference and index of Template Tags.