# OgImage 
type OgImage =
    {
        Url: string
        Alt: string option
        Width: int option
        Height: int option
    }
| | | |---|---| | Assembly | `Partas.Nacara.Plugins.OgImage` | The image a page is shared with: what a link preview shows. ## Declared inside | | | |---|---| | [`FrontMatterImage`](/Partas.Nacara.Plugins/reference/partas-nacara-plugins-ogimage/nacara-plugins/ogimage/frontmatterimage/) | What a page's front matter says about its image | ## Fields 
Url: string
An absolute url, or a path in the output such as `/images/card.png`. A path is made absolute with the site's origin, since a crawler reading the tag has no page to resolve it against. 
Alt: string option
What the image shows, for a reader who cannot see it. 
Width: int option
Width in pixels, so a crawler can lay the preview out before fetching it. 
Height: int option
Height in pixels.
## Functions and values 
[<Literal>] DataKey: string = "og-image"
Where the resolved image is stored on a page, as an `OgImage option`. `None` means the page has no image, having opted out or found no fallback. 
absoluteUrl (site: SiteInfo) (url: string) : string
The absolute url a crawler is given for an image. A path is taken from the root of the output, under the site's base url. Without an origin there is nothing to make it absolute with, so it stays root-relative. 
altKeys (value: string list) (options: OgImageOptions) : OgImageOptions
The front matter keys the alt text of a plain path is read from. | Parameter | | |---|---| | `value` | The value to use. | | `options` | The options so far. | 
apply (site: SiteInfo) (image: OgImage) (html: string) : string
A rendered page with its image described in the head. A head that already names an `og:image` is left alone: the theme chose. 
create () : IPlugin
Og-image tags, with the default options: front matter only, no fallback. 
createWith (configure: OgImageOptions -> OgImageOptions) : IPlugin
Og-image tags, configured. | Parameter | | |---|---| | `configure` | Given the defaults, the options to use. | 
defaultImage (value: OgImage) (options: OgImageOptions) : OgImageOptions
The image of every page nothing else gave one. | Parameter | | |---|---| | `value` | The value to use. | | `options` | The options so far. | 
defaults: OgImageOptions
excludeCollections (value: string list) (options: OgImageOptions) : OgImageOptions
Collections whose pages get no image at all. | Parameter | | |---|---| | `value` | The value to use. | | `options` | The options so far. | 
fallback (value: Page -> OgImage option) (options: OgImageOptions) : OgImageOptions
The image of a page whose front matter names none, asked before the default. | Parameter | | |---|---| | `value` | The value to use. | | `options` | The options so far. | 
fromFrontMatter (options: OgImageOptions) (mapping: YamlMappingNode) : FrontMatterImage
Read a page's image out of its front matter. | Parameter | | |---|---| | `options` | Which keys to read. | | `mapping` | The page's front matter. | 
frontMatterKeys (value: string list) (options: OgImageOptions) : OgImageOptions
The front matter keys a page names its image under, first match wins. | Parameter | | |---|---| | `value` | The value to use. | | `options` | The options so far. | 
image (url: string) : OgImage
An image with nothing but its url. | Parameter | | |---|---| | `url` | An absolute url, or a path in the output. | 
localPath (url: string) : string option
The output path a site-relative image is served from, when it is one. 
register (site: Site) : Site
Add og-image tags to a site. 
registerWith (configure: OgImageOptions -> OgImageOptions) (site: Site) : Site
Add og-image tags to a site, configured. | Parameter | | |---|---| | `configure` | Given the defaults, the options to use. | | `site` | The site being described. | 
resolve (options: OgImageOptions) (frontMatter: FrontMatterImage) (page: Page) : OgImage option
The image a page ends up with, front matter first and then the fallbacks. | Parameter | | |---|---| | `options` | The fallbacks. | | `frontMatter` | What the page's front matter said. | | `page` | The page, handed to `Fallback`. | 
tags (site: SiteInfo) (image: OgImage) (html: string) : string list
The head tags for an image, skipping any the head already has. | Parameter | | |---|---| | `site` | For the origin that makes a path absolute. | | `image` | What to describe. | | `html` | The rendered page, to see what its head already says. | 
withAlt (alt: string) (image: OgImage) : OgImage
The same image, with alt text. 
withSize (width: int) (height: int) (image: OgImage) : OgImage
The same image, with its dimensions in pixels.