解决方案:

Rails.application.routes.url_helpers.rails_representation_url(picture_of_car.variant(resize: "300x300").processed, only_path: true)

在此处提供了答案.

对于一个变体，您需要使用 rails_representation_url(variant) - 这将构建一个类似于 rails_blob_url 构建的 URL，但专门针对该变体.

for a variant you need to use rails_representation_url(variant) - this will build a url similar to the one that rails_blob_url builds but specifically for that variant.