Use imagor as Thumbnail Generator

OpenCloud creates previews (thumbnails) of images and documents, which are displayed in the file list and in the preview app. By default, the built-in thumbnails service generates these previews.

As of OpenCloud 9.0.0, you can replace the built-in thumbnail generator with imagor. imagor is a fast image processing server based on libvips and can read image formats that the built-in generator does not support.

This guide explains how to enable imagor in a deployment based on the opencloud-compose deployment example.

Benefits

Feature	Built-in generator	imagor
Previews for common formats such as JPEG, PNG, and GIF	Yes	Yes
Previews for HEIC and HEIF, for example iPhone photos	No	Yes
Previews for AVIF	No	Yes
Open HEIC, HEIF, and AVIF images in the preview app	No	Yes
Additional formats such as PSD, XCF, and BMP	No	With the ImageMagick variant
Additional container	No	Yes

The OpenCloud container image intentionally does not include a HEIC decoder. Without imagor, OpenCloud does not create previews for HEIC, HEIF, and AVIF files, and users can only download them.

How It Works

As of OpenCloud 9.0.0, the webdav service handles all thumbnail requests and manages the thumbnail cache. To create a preview, it sends the source image to a thumbnail generator. The built-in thumbnails service and imagor use the same interface, so imagor can replace the built-in generator without further changes.

The opencloud-compose deployment example provides a module that:

• Starts imagor as an additional container.
• Connects imagor to the OpenCloud container through an internal network without access to the internet.
• Configures OpenCloud to send preview requests to imagor.
• Enables previews for HEIC, HEIF, and AVIF files, including image sequences.

Prerequisites

• A running OpenCloud deployment based on opencloud-compose.
• OpenCloud version 9.0.0 or later.
• A current version of the opencloud-compose repository that contains the file thumbnails/imagor.yml.

If you are running an older OpenCloud version, follow the Standard Upgrade Guide and the Upgrade 9.x.x guide first.

All commands in this guide are run in the root directory of the opencloud-compose deployment.

Enable imagor

Update the opencloud-compose Repository

Update your local copy of the opencloud-compose repository:

git pull

Check that the imagor module is available:

ls thumbnails/imagor.yml

Add the Module to COMPOSE_FILE

Add thumbnails/imagor.yml to the end of the existing COMPOSE_FILE variable in your .env file, for example:

COMPOSE_FILE=docker-compose.yml:traefik/opencloud.yml:thumbnails/imagor.yml

Keep all files that are already part of your deployment.

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Make sure that the .env file contains only one active COMPOSE_FILE line. If there are several lines, only the last one is used.

Alternatively, add the module directly to the startup command:

docker compose -f docker-compose.yml -f traefik/opencloud.yml -f thumbnails/imagor.yml up -d

Restart OpenCloud

Apply the changes:

docker compose up -d

Docker Compose starts the imagor container and restarts OpenCloud. OpenCloud waits until imagor is ready.

Verify the Configuration

Check that the imagor container is running and healthy:

docker compose ps imagor

The status must be Up and (healthy).

Check that OpenCloud uses imagor as thumbnail generator:

docker compose exec opencloud printenv WEBDAV_THUMBNAILS_GENERATOR_URL

The output must be http://imagor:8000.

Finally, test the previews in the Web Client:

1. Upload a HEIC image, for example a photo taken with an iPhone.
2. Check that a preview is displayed in the file list.
3. Open the image. It is displayed in the preview app.

Previews are created when they are requested for the first time. This also applies to HEIC, HEIF, and AVIF files that were uploaded before you enabled imagor.

Optional Settings

You can adjust the imagor module with the following variables in your .env file:

Variable	Default	Description
IMAGOR_DOCKER_IMAGE	shumc/imagor	Container image of imagor.
IMAGOR_DOCKER_TAG	1.9.14	Version of the imagor container image.
IMAGOR_MAX_SOURCE_SIZE	50000000	Maximum size of a source image in bytes.
THUMBNAILS_ADDITIONAL_SOURCE_TYPES	image/heic,image/heif,image/avif,image/heic-sequence,image/heif-sequence	Comma-separated list of additional MIME types for which previews are created.

important

If you set THUMBNAILS_ADDITIONAL_SOURCE_TYPES, the value replaces the default list. To keep previews for HEIC, HEIF, and AVIF files, include their MIME types in your list.

If imagor cannot read a file of an additional type, no preview is created for this file.

Use the ImageMagick Variant

The ImageMagick variant of imagor supports additional formats such as PSD, XCF, and BMP. To use it, set the container image in your .env file and add the MIME types of the additional formats to THUMBNAILS_ADDITIONAL_SOURCE_TYPES:

IMAGOR_DOCKER_IMAGE=ghcr.io/cshum/imagor-magick
THUMBNAILS_ADDITIONAL_SOURCE_TYPES=image/heic,image/heif,image/avif,image/heic-sequence,image/heif-sequence,<additional-mime-types>

Restart OpenCloud to apply the changes:

docker compose up -d

vorsicht

The ImageMagick variant is slower, uses more memory, and has a larger attack surface than the standard image. Use the standard image unless you need the additional formats.

Security

The imagor module is configured with restrictive security settings:

• imagor runs in an internal network and cannot connect to the internet.
• imagor only processes images that OpenCloud sends to it. Loading images from URLs is disabled.
• The container runs with a read-only file system, without Linux capabilities, and with no-new-privileges.

Do not publish the imagor port. imagor does not authenticate requests.

Limitations

• Source images larger than 7680 × 7680 pixels are not processed.
• Animated images with more than 100 frames are not processed.
• Files in end-to-end encrypted folders have no server-side previews, because the server only stores encrypted data.

Disable imagor

To return to the built-in thumbnail generator:

1. Remove thumbnails/imagor.yml from COMPOSE_FILE in your .env file.

2. Apply the changes and remove the imagor container:

   docker compose up -d --remove-orphans

Previews for HEIC, HEIF, and AVIF files are no longer created.

Troubleshooting

No Previews Are Displayed for HEIC Files

• Check that you are running OpenCloud version 9.0.0 or later.
• Check that thumbnails/imagor.yml is part of COMPOSE_FILE.
• Check that OpenCloud uses imagor as described in Verify the Configuration.
• If you set THUMBNAILS_ADDITIONAL_SOURCE_TYPES, check that the list contains image/heic.

The OpenCloud Container Does Not Start

OpenCloud waits until imagor is healthy. Check the status and the logs of the imagor container:

docker compose ps imagor
docker compose logs --tail=40 imagor