Minimal preview creation

From version 10.4, core preview sizes (those with IDs 'col', thm' and 'pre') will always be created, either at upload time or when previews are recreated. This will occur even if one of the following options is enabled
• $offline_job_queue
• $enable_thumbnail_creation_on_upload
• $preview_generate_max_file_size
All other previews, including e.g. image tiles, image alternatives, ffmpeg alternatives and unoconv derivatives will be created later by the relevant offline scripts.

Excluding file types from minimal preview generation

You can optionally use the following configuration option to prevent immediate creation of core preview sizes ('col', 'thm' and 'pre') for the specified file extensions when one of the offline preview options are configured.
$minimal_preview_creation_exclude_extensions = [];
$minimal_preview_creation_exclude_extensions[] = "tif";