resize from small images to large

Question

I want to create large images though my original image is smaller.

I have original images 1024x768 in my media library, and i want to resize these images to 1920x1080px in my WordPress posts.

I used add_image_size( 'large', 1920, 1080, true );

but it is not working, please tell me what to do to get large image sizes

Answer 1

Found a solution here that is working:

http://www.binarynote.com/how-to-perfectly-upscale-image-in-wordpress.html

function binary_thumbnail_upscale( $default, $orig_w, $orig_h, $new_w, $new_h, $crop )
{
    if ( !$crop ) return null; 
    $aspect_ratio = $orig_w / $orig_h;
    $size_ratio = max($new_w / $orig_w, $new_h / $orig_h);
    $crop_w = round($new_w / $size_ratio);
    $crop_h = round($new_h / $size_ratio);
    $s_x = floor( ($orig_w - $crop_w) / 2 );
    $s_y = floor( ($orig_h - $crop_h) / 2 );
    return array( 0, 0, (int) $s_x, (int) $s_y, (int) $new_w, (int) $new_h, (int) $crop_w, (int) $crop_h );
}
add_filter( 'image_resize_dimensions', 'binary_thumbnail_upscale', 10, 6 );

As gurung says, it is not ideal and Wordpress doesn't upscale for a reason but if you know what you do and use Wordpress more as a framework to suit your specific needs, this will get the job done. In my case, it solves some grid layout issues.

I hope it helps.