I am using odoo online where I have created a custom model (x_images) for a custom app (Images). 

I am using a kanban view to list images records with actual images (image widget). My problem is that the images uploaded (in x_image field) are quite big (3mb) so the kanban view performance is really bad. I want to create thumbnails in field (x_image_s) and use that field instead of x_image. I tried to use tools.image_get_resized_images() in the compute functionality (from GUI since I am using Odoo Online hosted by Odoo) to store a resized image in x_image_s but couldn't make it work. How can I solve my issue?