class ActiveStorage::Variant

def specification
  @specification ||=
    if WEB_IMAGE_CONTENT_TYPES.include?(blob.content_type)
      Specification.new \
        filename: blob.filename,
        content_type: blob.content_type,
        format: nil
    else
      Specification.new \
        filename: ActiveStorage::Filename.new("#{blob.filename.base}.png"),
        content_type: "image/png",
        format: "png"
    end
end