Storefront themes “Gridport” theme, change the size of the blog thumbnail

Change the size of thumbnail that appears on the Grdidport Blog page.

The change here is for the thumbnails you see when you click blog on your menu or click a blog category and see a list of posts. These are created when you set a image to be “featured image” in your post.

to change it you would have to get into the PHP source code. A very simple edit.
Specifically you have to edit the file theme-functions.php which is in the sub folder “includes” in the Gridport theme folder. New to PHP editing? see the Tools note at the end of this post.

Save a copy of your the PHP file somewhere safe before editing so you can always go back if you mess up something.

about line 590 you will find the highlighted code.

// Add support for WP 2.9 post thumbnails
if ( function_exists( 'add_theme_support' ) ) { // Added in 2.9
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size( 55, 55, true ); // Main theme thumbnails
	add_image_size( 'thumbnail-large', 75, 75, true ); // Large thumbnails
	add_image_size( 'thumbnail-wide', 300, 100, true ); // Wide thumbnails
	add_image_size( 'main-image', 285, 280, true ); // Main (latest) image
	add_image_size( 'main-image-pictures', 290, 280, true ); // Main (pictures) image
	add_image_size( 'lead-image', 540, 250, true ); // Post Page Main image
}

Change those numbers 75, 75. Remember if you make it too big you may end up with blank lines where there was not enough room next to the thumbnail for a long word.
You will find it effects all new uploads of featured image. A thumbnail rebuild plugin may save you having to upload existing ones again. Search this in plugins “AJAX Thumbnail Rebuild” try that one first.
Remember when uploading images, set to full size and use as featured image.