I'm glad that WP 4.4. ships with a built-in responsive image feature. But I'm not that happy with it.

I have set up some custom image sizes in my functions.php:

add_image_size('post-thumbnails', 600, 600, true);
add_image_size('news-large', 1024, false);
add_image_size('news-small', 500, false);
add_image_size('3-col', 500, 375, true);
add_image_size('presscutting', 600, 850, true);
add_image_size('medium-large', 768, false); // just added today for devices support
add_image_size('full-feature-image', 2000, false);
add_image_size('gallery-image', 800, 600, true);

As I figured, images that aren't cropped (cropping set to false) are added to the srcset. An image is output in the frontend like (line breaks added for better readability):

<img width="2000" height="1335"
class="attachment-full-feature-image size-full-feature-image"
http://mywebsite.com/cms/wp-content/uploads/2015/03/image-300x200.jpg 300w, 
http://mywebsite.com/cms/wp-content/uploads/2015/03/image-768x513.jpg 768w, 
http://mywebsite.com/cms/wp-content/uploads/2015/03/image-1024x683.jpg 1024w, 
http://mywebsite.com/cms/wp-content/uploads/2015/03/image-500x334.jpg 500w" 
sizes="(max-width: 2000px) 100vw, 2000px">

But now my problem: On my screen, only the images specified with 1024px width are shown, although it hast a 1600px screen resolution. So all the images look blurry.

How can i make WP and/or my browser use the 2kpx image instead? Would I have to add new image sizes for, let's say 1280px, 1440px, 1600px, 1968px? Or is there a simpler way of telling WP / the browser to use the larger image instead of showing a blurry and way too small version?

  • Can you please try this out with the correct way to use add_image_size? You always set the width argument to false - this should be an integer (third argument).
    – fischi
    Dec 10, 2015 at 9:33
  • Ok, done that and added height-value of 9999. Resized thumbnails. No avail.
    – rob_st
    Dec 10, 2015 at 9:44
  • The default of the max_srcset_image_width filter is 1600.
    – birgire
    Dec 10, 2015 at 10:06
  • Good to know @birgire - but that doesn't help much. How do I change it (there seems to be no documentation yet) - and will a change solve my problem?
    – rob_st
    Dec 10, 2015 at 14:38

2 Answers 2


Concerning documentation there is this blog post on the Make Blog:

Responsive Images in WordPress 4.4

To increase the 1600px limit mentioned in the comments try this:

add_filter('max_srcset_image_width', function($max_srcset_image_width, $size_array){
    return 2000;
}, 10, 2);

Finally as already mentioned you should fix your calls to add_image_size

add_image_size('news-large', 1024, false);

needs to be

add_image_size('news-large', 1024, 0, false);
  • Thank you. I've set the height to 9999 - does it make any difference? I'll try it out.
    – rob_st
    Dec 11, 2015 at 8:40
  • Thank you, that made it work. Although it is basically the same answer as this one and actually I prefer named functions - I accepted yours because you were first :-)
    – rob_st
    Dec 14, 2015 at 14:50
  • I think this might be the answer I need, but I don't know what value $size_array should have. Sep 18, 2018 at 14:57

I solved the same issue by adding an extra size to the srcset with a filter function that you can add in your functions.php:

function filter_max_srcset( $max_width, $size_array ) {
    if ( $size_array[0] === 1800 ) {
        $max_width = 1800;
    return $max_width;
add_filter( 'max_srcset_image_width', 'filter_max_srcset', 10, 2 );

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