Extension:PageImages/zh

The PageImages extension collects information about images used on a page.

Its aim is to return the single most appropriate thumbnail associated with an article.

Since MediaWiki 1.29, PageImages provides OpenGraph protocol metadata for articles on the wiki for 3rd parties like Facebook to extract.

API
The PageImages extension provides image information by adding a  to the  API for.

配置
$wgPageImagesBlacklist is an array of sources for image blacklists. Blacklisted images will never be selected as page images. Examples:

More than one source can be used at the same time.

$wgPageImagesBlacklistExpiry determines how long the blacklist will remain cached, in seconds. Default: 15 * 60 (15 minutes).

$wgPageImagesExpandOpenSearchXml if set to true, PageImages will override the image detection in the API module with its own, more accurate results. 默认为“false”.

$wgPageImagesNamespaces is an array of namespaces PageImages will be activated on. 默认为“NS_MAIN”.

The blacklist itself should contain a wikilinks to blacklisted files, the rest of content is irrelevant (and can contain links to other pages). 例如：

Remember that file links that result in images being added to the page will not work (these files are blacklisted for a reason, right?), so don't forget the  in front of the links.

工作原理
When a page is saved with a local image, the parser runs the hooks  and. The PageImages extension responds to these (and other hooks) and inserts a new property for the page into the table. The property name is  and its value is the name of the image.

The extension only stores the chosen image name. Other features may display the image, such as Page information, Hovercards, and Mobile search while typing.

How can I check which image is associated with a page?
Page images will be listed on the ?action=info page.

How does it select images?
All images in the page are collected and a score for each image is calculated. The image with the highest score is selected as the page image. If the wiki is configured such that images contain metadata that specifies images are not freely licensed, the image with the best score that is also freely licensed is also stored. If no suitable image is found or all the images score badly (i.e. has a negative score), the page will not have any images.

If $wgPageImagesLeadSectionOnly is true, only images in the lead section will be considered. Currently it is true for only Wikipedia projects, all other projects can pull images from outside the lead.

How are images scored?
The best possible page image on Wikimedia wikis is one of the first four images in an article which has a width/height between 400-600px and a height/width which is twice the value of the other dimension.


 * The algorithm is configurable.
 * Scores are calculated by a combination of:
 * Image widths as defined in $wgPageImagesScores['width']
 * In Wikimedia wikis, images smaller than 119 pixels are weighted highly negatively. Images with widths between 400px-600px are favoured, with a preference for the lower bound.
 * Images inside galleries are scored separately using $wgPageImagesScores['galleryImageWidth']
 * In Wikimedia wikis gallery images which are smaller than 100 are disregarded.
 * Position in document is also considered as defined in $wgPageImagesScores['position']
 * On Wikimedia wikis, only the first 4 images that appear in the document are considered.
 * The ratio of the image's width to height is considered $wgPageImagesScores['ratio']
 * On Wikimedia wikis the best possible images are images where the height is half the width or the height is double the width. Any images for which the ratio is less than 0.5 will score negatively and be discarded.

Be more technical please...
Pageimages populates images whenever the LinksUpdate hook runs.

In PageImages this is executed in LinksUpdateHookHandler::doLinksUpdate

Can I exclude certain page images?
Yes! There is a blacklist on every wiki that administrators can edit, at MediaWiki:Pageimages-blacklist (example). Any images that appear here will not be page images for any article.

What about just for one particular article?
Sadly not at the current time. Please use the blacklist or move the image outside the lead section.

How can I see the page image for a page?
Using the  link in the sidebar (or adding  to the URL) you'll be able to see the current image choice.

How can I purge a bad image?
The pageimage only changes when a link in an article changes. For emergencies, please add/remove links from the page, reverting if necessary. Purging will not work. For larger emergencies please file a Phabricator ticket.

Why is my page image a blank box?
This likely relates to video content in your article. If a video file begins with a blank screen, that will become the default thumbnail for the video and if used as the page image, it will become the page image. We are currently working on a fix for this, that will allow you to change the default thumbnail of a video. See: phab:T92457 and phab:T22647 for further information.