How to work with images using damfn

This page explains how to work with images and other assets stored in the Magnolia Digital asset management using damfn templating functions in template scripts.

Imaging modules

If you use a Magnolia bundle, the required and optional modules are already included.

If you created a custom webapp, add the following modules in the pom file of the webapp of your bundle. The modules may have dependencies to other modules but these dependencies are handled by Maven dependency management.

Required modules

Modules required for basic image operations.

artifactId version

artifactId	version
`magnolia-dam-imaging`	3.0.4
`magnolia-imaging-support`	3.4.4

magnolia-dam-imaging

3.0.4

magnolia-imaging-support

3.4.4

Optional modules

Modules required when using a Rendition of an asset, such as size variations of an image. Recommended.

artifactId version

artifactId	version
`magnolia-site`	1.4
`magnolia-templating-essentials-imaging`	1.5.2

magnolia-site

1.4

magnolia-templating-essentials-imaging

1.5.2

Selecting the image in dialog with a link field

To select an image in a dialog use the Link field, it stores a reference to the selected asset.

Example - code fragment from a dialog definition

form:
  tabs:
    - name: tabImage
      fields:
        - name: image
          class: info.magnolia.ui.form.field.definition.LinkFieldDefinition
          targetWorkspace: dam
          appName: assets
          identifierToPathConverter:
            class: info.magnolia.dam.app.assets.field.translator.AssetCompositeIdKeyTranslator
          contentPreviewDefinition:
            contentPreviewClass: info.magnolia.dam.app.ui.field.DamFilePreviewComponent

Displaying an image

To render an image, you need to get a link to the asset. Use the link as a value in the src attribute of the img element.

Getting an image link with an itemKey

Use the #getAssetLink(itemKey) method if you have the itemKey of the image. See: Get link for asset. For instance, the textImage component stores the itemKey in the image property. This is a very common use case.

Example: Getting an image link with an itemKey. Assume that this code is executed in a component template. The current content node has a property named image where the itemKey is stored.

[#assign imgItemKey = content.image!]
[#if imgItemKey??]
    [#assign imgRef = damfn.getAssetLink(imgItemKey)!]
    [#if imgRef??]
        <img src="${imgRef}"/>
    [/#if]
[/#if]

Getting an image link for an asset

Use the #getLink() method if you already have the asset. Since an Asset object is a Java bean you can use its public method #getLink(). You may even use the dot notation.

Example: Getting an image link for an asset

[#assign myAsset = damfn.getAsset("jcr","/photos/pool.jpg")!]
[#if myAsset??]
    <img src="${myAsset.getLink()}"/>
[/#if]

[#assign myAsset = damfn.getAsset("jcr","/photos/dilbert.jpg")!]
[#if myAsset??]
    <img src="${myAsset.link}"/>
[/#if]

Displaying resized images

Best practice

If you need different sizes of the same image, do NOT upload multiple copies (variations) of the same image to your DAM repository. Instead, upload the image only once and define image size variations in your theme.

Defining image variations

Configure your image variations in a theme. Each variation should be a node under <my-theme>/imaging/variations. The variation node name such as small-square is what you will be referencing in your template scripts. It is also known as rendition name.

Example: Defining three image variations in a theme.

Theme variations configuration

Property Description

Property	Description
`imaging`	optional Image variations for the various renditions of an image on the page.
`class`	required VariationAwareImagingSupport provides support for variations.
`enabled`	optional Enables and disables variation support.
`variations`	required Map of image variations.
`<variation‑name>`	required The name of the variation, a.k.a the rendition name. Choose a name that describes the variation. The name is used in template scripts to reference the variation. Add one node for every variation.
`class`	required You can use one of the available classes or create a custom one. The available properties depend on the class used for the variation. Any custom class must implement Variation. Magnolia Templating Essentials module provides: SimpleResizeVariation that resizes images to a defined size in pixels (see below for available properties). ImageOperationProvidingVariation that allows you to create your own image operation chain using the `mte` image generator.
`<properties>`	Add properties that are supported by the class used.

imaging

optional

Image variations for the various renditions of an image on the page.

class

required

VariationAwareImagingSupport provides support for variations.

enabled

optional

Enables and disables variation support.

variations

required

Map of image variations.

<variation‑name>

required

The name of the variation, a.k.a the rendition name. Choose a name that describes the variation. The name is used in template scripts to reference the variation. Add one node for every variation.

class

required

You can use one of the available classes or create a custom one. The available properties depend on the class used for the variation. Any custom class must implement Variation.

Magnolia Templating Essentials module provides:

SimpleResizeVariation that resizes images to a defined size in pixels (see below for available properties).
ImageOperationProvidingVariation that allows you to create your own image operation chain using the mte image generator.

<properties>

Add properties that are supported by the class used.

On the node /modules/site/config/themes/<your-theme>/imaging you must specify the class property. The used class must implement ImagingSupport. MTE module provides VariationAwareImagingSupport which is a good choice for our use case here.

Add one node for every required variations below <your-theme>/imaging/variations. The name of such a node is the name of the variation. also known as the rendition name. In the example above we have defined the renditions small-square, thumbnail and medium.

For every variation you have to configure some properties. The available properties depend on the class you use in the variation. You can implement your own class. The definition class must implement the Variation interface.

In the example above we use SimpleResizeVariation. This class is provided by the magnolia-templating-essentials-imaging module. Your webapp bundle must contain the module.

Properties of SimpleResizeVariation:

Property Description

class

required

Class must implement SimpleResizeVariation.

height

optional*

An integer to define the height in pixels. You must configure either height or width or both.

width

optional*

An integer to define the width in pixels. You must configure either height or width or both.

crop

optional, default is true

Defines whether cropping the image is allowed to fit the desired aspect ratio.

Example: A source image in the DAM is 800x800 px (square). In a variation you define the desired target size as 200x100 (rectangle) so the aspect ratio changes. By default crop=true which means cropping is allowed. Magnolia first resizes the image to 200x200 and then crops equally from the top and bottom to reach 200x100. No image distortion happens. If you set crop=false Magnolia squishes the image, resulting in distortion, to achieve the desired 200x100.

You must define either width or height. If you do not define either, the renderer internally throws an ImagingException but displays the default size, the size of the original uploaded image. When you define both width and height, the image is resized accordingly and is cropped if the ratio does not fit. If you define only width or only height, the other property is calculated accordingly based on the ratio of the original image.

Make sure the site where you want to display the image variations references the theme. In the Site app, the theme name property must be the same as the main node of the configured theme, in this example my-theme.

Getting an image variation

Example: Getting an image variation (asset rendition) with an itemKey. Assume that content in this example stores the itemKey in the image property.

[#assign imgItemKey = content.image!]
[#if imgItemKey??]
    [#assign myMediumRendition = damfn.getRendition(imgItemKey, "medium")!]
    [#if myMediumRendition??]
        <img src="${myMediumRendition.getLink()}"/>
    [/#if]
[/#if]

Example: Getting an image variation (asset rendition) for an asset.

[#if myAsset?? && myAsset.isAsset()]
    [#assign myThumbnail = damfn.getRendition(myAsset, "thumbnail")!]
    [#if myThumbnail??]
        <img src="${myThumbnail.getLink()}"/>
    [/#if]
[/#if]

Image variation cache

Magnolia caches image resources to improve performance. Any dynamic images generated by the Imaging module are also cached at two levels: in the imaging workspace and in the actual cache like any other page or document. This means that once the system generates an image, you keep getting the same cached image on subsequent requests.

Disable image cache during development

During developing it is helpful to disable caching of generated images completely. Go to Configuration > /server/filters/servlets/ImagingServlet/parameters, create a new property storeGeneratedImages, and set its value to false.

Remove the property or to set it to true after having finished image variation development. Do not use this property in your production environment!

Deleting imaging variations in the imaging workspace

Once image variations are stored in the imaging workspaces, they remain there. After you remove the storeGeneratedImages property, any cached image variations are served from the imaging workspace again. Delete the nodes from the workspace.

Option 1: Groovy script. In the script, examples-theme is the name of your theme. You can run this script in the Groovy console or add a new script and run it.

session = MgnlContext.getJCRSession('imaging')
images = session.getNode('/examples-theme')
images.remove()
session.save()

Option 2: Delete the nodes in the imaging workspace in JCR Browser app.