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 tileImage="true" footerHeight="50">
        <scale>300</scale>
        <scale>900</scale>
        <scale>1800</scale>
        <scale>3200</scale>
        <useFor>
            <!--view>fullscreen</view-->
        </useFor>
        <tileSize>
            <scaleFactors>4</scaleFactors>
            <size>1024</size>
        </tileSize>
    </zoomImageView>
</viewer>

The individual configuration parameters are explained below:

Parameter	Description
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.

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>