Other image options
Preferred Formats
This feature is still in development and not yet in the release version.
The preferredFormats property is a feature of the IIIF Image API version 3.
It allows the publisher to suggest that the client ask for a different format from the default JPEG. For example, if publishing line art, .png might be better.
Canvas Panel (and <img-service/>) will use the preferred format(s) automatically if consuming a IIIF Image API 3 endpoint (and if they are available), but it also supports the concept as a client property; using Canvas Panel on a web page you can state a preference as a consumer, regardless of whether the server has this property. This works for Image API version 2 services as well:
<canvas-panel iiif-content=".." preferred-formats="png"></canvas-panel>
<canvas-panel iiif-content=".." preferred-formats="webp,jpg"></canvas-panel><!-- equivalent to just "webp" -->
(Demo forthcoming when feature is implemented)
If the format is not available, the tag will fall back to the default jpg.
Preferred Qualities
This feature is still in development and not yet in the release version.
This is very similar to the behaviour of preferred-formats. It allows you to provide a hint to Canvas Panel that you would like a quality (in IIIF Image API terms) that is different from default. If the quality is unavailable, canvas panel will fall back through the list, or request default if there is no other possibility.
Unlike preferred formats, there is no equivalent preferred qualities in the Image API - the provider of the service can choose what default means, but they can't choose what png means - the two features are not exactly equivalent.
If you know that your application is making calls to a server that provides special or custom quality support, this is how you can pass the required values:
<canvas-panel iiif-content=".." preferred-quality="bitonal"></canvas-panel>
<!-- or same for image-service -->
<image-service src=".." preferred-formats="webp" preferred-quality="posterised,craquelure"></image-service>