image_size with respect to aspect ratios

Question

I have image assets that I load externally and insert programmatically. There are 3 different asset classes:

 landscape, portrait, and 1:1

The default image_sizes are creating a lot of clutter that's of no use to me. So I've disabled those and added my own custom ones.

But Wordpress is generating resized assets that fits every asset class, despite it only being relevant for 1/3rd. Since the only condition for making a resized asset seems to be exceeding a width/height threshold.

Is it possible to indicate which specific image sizes you want Wordpress to create when you insert an image asset at file_put_contents or wp_update_attachment_metadata, specifically for this one asset, instead of dictating the sizes that should be created globally? Such that we only create the extra sizes relevant to landscape assets when we know we're insert landscape assets?

Or alternatively, can you create a custom image_size that factors in aspect ratio and not just raw pixel dimensions?

Answer 1

Right before image subsizes are created, there's a filter called intermediate_image_sizes_advanced that lets you modify the list of sizes.

Here's code that you could expand on — right now it just removes the thumbnail as a proof of concept:

function remove_image_sizes_before_generation( $new_sizes, $image_meta, $attachment_id ) {
    $width = $image_meta[0];
    $height = $image_meta[1];

    // ... Calculate aspect ratio and remove the image sizes that aren't relevant
    unset( $new_sizes['thumbnail'] );

    return $new_sizes;
}

add_filter( 'intermediate_image_sizes_advanced', 'remove_image_sizes_before_generation', 10 , 3 );

The nice thing about doing it this way is that the image will then "remember" what sizes it doesn't have, even if they are registered sizes — for example, it won't show up in drop-downs where you insert the image.