1.11.3 Image view configuration

For the image display OpenSeadragon based on the IIIF Image API is used. A separate configuration block exists for the display, in the <viewer> section.

Goobi viewer installations using the crowdsourcing module can configure the image display there separately under <zoomCrowdsourcingView> if desired.

The configuration block has the following form:

config_viewer.xml

<viewer>
    <zoomImageView type="default" tileImage="true" footerHeight="50">
        <scale>300</scale>
        <scale>900</scale>
        <scale>1800</scale>
        <scale>3200</scale>
        <useFor>
            <!--view>fullscreen</view-->
            <!--mimeType>image/png</mimeType-->
        </useFor>
        <tileSize>
            <scaleFactors>4</scaleFactors>
            <size>1024</size>
        </tileSize>
        <navigator enabled="false" />
        <thumbnailGallery enabled="false" />
        <doublePageNavigation enabled="true" default="false" />
    </zoomImageView>
</viewer>

The individual configuration parameters are explained below:

@type	Specifies the type of image display. Possible options are default and sequence. The standard image display is default, while the value sequence enables navigation through the images without reloading the page. You can navigate between the images in the image container by scrolling up and down. The default value is default.
@tileImage	Specifies whether to display the image as a whole or tiled.
@footerHeight	The absolute height of the footer in pixels. To switch off the footer completely, you can enter a value of "0" here.
/scale	This configuration is only considered for tileImage="false". Then it specifies the width of the displayed image in pixels. This is not the width of the image display defined in the HTML code, but the size of the image loaded for display. This configuration can be repeated at will to display the image in different resolutions. Larger versions of the image are reloaded when the image display is zoomed.
/tileSize	This configuration is only considered for tileImage="true". It consists of two sub-configurations: scaleFactors and size.
/navigator/@enabled	If active, a small preview is available within the image display to show where you are in the overall image. The default value is false.
/thumbnailGallery/@enabled	If active, thumbnail navigation is available within the image display. This setting only makes sense with the type="sequence". The default value is false.
/doublePageNavigation/@enabled	If a work has more than one image, it can be displayed in a double-page view. Support for this can be switched on and off globally with the enabled attribute. The default value is true.
/doublePageNavigation/@default	The default attribute can be used to control whether the double page view is also active by default when a work is opened. The default value is false.

scaleFactors is a comma-separated list of scaling factors by which the tiles for the display are scaled down. For example, if factors 1 and 32 are specified, only tiles that display the image in 1/32 scale will be displayed. When zooming in, these tiles are replaced by tiles that show the image in full resolution. It is common, but not mandatory, to scale in powers of two. However, these values are only guidelines for the underlying OpenSeadragon implementation, which typically uses multiple magnifications between the specified values.

size determines the size of the individual tiles in pixels. Which section of the actual image they represent depends on the scaleFactor used. With a scaleFactor of 4 and a size of 512, a 2048 x 2048 pixel section of the original image is displayed per tile.

This configuration can be repeated at will if you want to use different tile sizes.

By default, the images are always scaled to the width of the image container to ensure consistent display. However, this leads to problems if, for example, a book spine or an internal leporello is digitized. Then the displayed images are either enormously large and long, or extremely narrow and wide.

To counteract this effect, the Goobi viewer now limits the image display to a height of 1200px as soon as certain threshold values are exceeded. The threshold value is calculated by dividing the image width by the image height. It is set with the following configuration element:

config_viewer.xml

<viewer>
    <limitImageHeight lowerRatioThreshold="0.3" 
                      upperRatioThreshold="3.0">true</limitImageHeight>
</viewer>