I am developing a child theme based on the twentyten theme and now i notice the featured image in the WP backend (wp-admin) shows the wrong scaled image.

It shows the "twenty ten" size, meaning an image scaled to x198.

How do i show the featured image of my chosen size???


  • Where exactly do you want to use/see your custom image size output? Also: how/where did you define your custom image size(s)? Commented Mar 2, 2012 at 22:01
  • @ChipBennett, i defined the custom sizes in my child theme's functions.php. The custom images work fine in my child theme, it is just the backend featured image, which is the one defined by Twenty Ten theme and not my child theme. I thought i overwritten it by adding this to my child theme's functions.php add_theme_support('post-thumbnails'); set_post_thumbnail_size(150, 150, false);
    – alex
    Commented Mar 2, 2012 at 22:17
  • "the backend featured image" - WHERE EXACTLY are you seeing this featured image? Are you talking about the "Featured Image" meta box on the Edit Post screen, or somewhere else? Commented Mar 2, 2012 at 22:26
  • sorry yes that's the one: the featured image in the meta box on the Edit Post screen.
    – alex
    Commented Mar 2, 2012 at 22:35

2 Answers 2


First: why do you care the size of the thumbnail displayed in the "Featured Image" meta box on the Edit Post screen?

Second: that image size isn't defined by Twenty Ten (or any other Theme). It's defined by core, and is actually simply calling the original image size, and scaling it.


Whoops; that was wrong. :) That Meta Box is apparently displaying the 'thumbnail' image size. (And I had forgotten that one of my primary beefs with Twenty Ten / Twenty Eleven is that they screw with the default thumbnail size.)

Start here:

set_post_thumbnail_size( HEADER_IMAGE_WIDTH, HEADER_IMAGE_HEIGHT, true );

So, you were on the right track. :)

Next go to the define calls:

define( 'HEADER_IMAGE_WIDTH', apply_filters( 'twentyten_header_image_width', 940 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'twentyten_header_image_height', 198 ) );

So, the easiest way to override those defined sizes is via the twentyten_header_image_width and twentyten_header_image_height filters. e.g., in your Child Theme's functions.php file:

function wpse44268_filter_twentyten_header_image_width( $width ) {
    return '150';
add_filter( 'twentyten_header_image_width', 'wpse44268_filter_twentyten_header_image_width' );

function wpse44268_filter_twentyten_header_image_height( $height ) {
    return '150';
add_filter( 'twentyten_header_image_height', 'wpse44268_filter_twentyten_header_image_height' );

These will define the post thumbnail as 150x150. Change the return values to suit your needs.

  • 1/ the thumbnail displays a wrong part of the image 2/ i do think it's in Twenty Ten as 198px height isn't the original height and i see define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'twentyten_header_image_height', 198 ) ); and the thumbnail has this height. Also when i add a custom post type with post thumbnail support it will show the featured image dimensions i have defined for the custom post type. Really like to show the proper feature dimensions, so
    – alex
    Commented Mar 2, 2012 at 23:38
  • See updated answer; while I'm still not sure why the cropping of the image in that meta box is a big deal, you're right that Twenty Ten is mucking with the thumbnail image size. Commented Mar 2, 2012 at 23:53
  • Tx for the explanation, i am almost there. I have used your code suggestions, but i had to alter TwentyTen functions.php as well. Just this tiny bit set_post_thumbnail_size( HEADER_IMAGE_WIDTH, HEADER_IMAGE_HEIGHT, true); to set_post_thumbnail_size( HEADER_IMAGE_WIDTH, HEADER_IMAGE_HEIGHT, false); I have tried to add set_post_thumbnail_size( HEADER_IMAGE_WIDTH, HEADER_IMAGE_HEIGHT, false); to my child functions.php, but it still crops the image like it is set to true. As i don't want to alter the parent theme i am wondering how i can make this work from child's functions.php
    – alex
    Commented Mar 3, 2012 at 12:31
  • oh and another thing i notice. I have to delete the images and reupload the images to get the dimensions change to work. Which i don't understand as the same image formats are already in the uploads directory.
    – alex
    Commented Mar 3, 2012 at 12:36
  • Just try regenerating your thumbnails. Use a Plugin like Regenerate Thumbnails or Ajax Thumbnail Rebuild. Commented Mar 3, 2012 at 14:46

Changing the header image size to change the thumbnails size! You can do this without touching the parent theme file - in fact, any update will likely break your custom code. This is the point of child themes…

All you need to do is use add image size in your child theme:

 if ( function_exists( 'add_image_size' ) ) { 
    add_image_size( 'my-new-thumb', 150, 150,false );

And call this into the post_thumbnail in your template.

  • For one, the filters are applied from the child theme, so the parent one is not touched in the above answer. For another the OP was asking about the backend. Ain't no template used there... Commented Oct 26, 2012 at 1:47

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