UniWiki:Manual of Style/Images: Difference between revisions

An image sometimes includes a familiar object to communicate scale. Such ''[[Wikipedia:Fiducial marker|fiducial markers]]'' should be as culturally universal and standardized as possible: [[Wikipedia:Ruler|rulers]], [[Wikipedia:Match|matches]], [[Wikipedia:Battery (electricity)|batteries]], [[Wikipedia:Playing card|playing cards]], [[Wikipedia:Pen|pens]]/[[Wikipedia:Pencil|pencils]], [[Wikipedia:CD|CDs]]/[[Wikipedia:DVD|DVDs]], [[Wikipedia:Soda can|soda cans]], [[Wikipedia:Football (ball)|footballs]] (soccer balls), people, vehicles, and famous structures such as the [[Wikipedia:Eiffel Tower|Eiffel Tower]] are good choices, but many others are possible. Such objects as coins, banknotes, and sheets of paper are less satisfactory because they are specific to given locales, but may be better than none at all since at least the general scale is still communicated.

*An image's size is controlled by changing its width{{snd}}after which software automatically adjusts height in proportion. (Most references to an image's "size" really mean its width.)

Images can greatly increase the [[bandwidth (computing)|bandwidth]] cost of viewing an article{{snd}}a consideration for readers on slow or expensive connections. Articles carry reduced-size [[thumbnail]]s instead of full images (which the user can view by "clicking through" the thumbnail) but in some file types a thumbnail's reduced dimensions doesn't translate into a concomitant reduction in file size. (In most browsers you can see a thumbnail's size by right-clicking for its "Properties".)

* [[GIF]] images with a frame size larger than 12.5 million pixels (measured as pixel height × pixel width × number of frames in the animation) cannot currently be displayed in thumbnail form in Wikipedia articles. A thumbnail of a GIF image can be considerably larger in kilobytes than the original image file.

* Animated [[GIF]] images have a few additional restrictions. Images larger than 12.5 million pixels (measured as pixel height × pixel width × number of frames in the animation) currently will only show the first frame of the animation in a thumbnail. When not using a GIF animation at its original frame size, consider creating an Ogg [[Theora]] movie of the animation.

* The [[Portable Network Graphics|PNG]] format is useful for storing graphics that contain text, line art, or other images with sharp transitions. It can achieve the same graphical results as a GIF file, and in many cases do so with a higher rate of [[file compression]]. For this reason, PNG format files are usually preferred to the GIF format.  (However, for certain types of images, PNG thumbnailing is not as efficient as GIF thumbnailing, when Wikimedia GIF thumbnailing is enabled.) For images with substantial editing, or for which further editing may be warranted, uploading a PNG as well as a JPEG is common (PNG is lossless compression, so repeatedly saving edits on a PNG will not result in loss of quality.)

* A [[JPEG]] or other compressed image format can be much smaller than a comparable GIF or PNG format file. When there is no apparent difference in quality, such as with a photograph that has no sharp graphical transitions, a compressed image format such as JPEG may be preferable for reasons of download performance. Wikipedia is often able to achieve much better compression of JPEG photograph thumbnails than comparable PNG images, and with little perceptible loss of quality. Repeatedly loading and resaving an image as JPEG will result in loss of quality, however, as will using low settings for the JPEG; as such, if you've made edits, it can be helpful to save a PNG or TIFF copy before closing the image editor and upload that as well; this copy can then be used to generate a new JPEG after further editing.  

* Where an image consists solely of line art, charts text and simple graphics, an [[Scalable Vector Graphics|SVG]] file can be significantly smaller than other graphics formats. This is because the data is encoded as a series of drawing commands, rather than as [[raster graphics]]. There are [[open source]] applications available for rendering graphics in SVG format. However, SVG thumbnails are rendered as PNGs.

<code>px</code> works the same as <code>upright</code> for users with the usual base width setting of 220px, but works counterintuitively for readers whose base width is set to a different value (see [[Help:Preferences#Files]]). For example, an image coded <code>275px</code>{{mdashb}}presumably to make it wider than most images on a particular page{{mdashb}}is actually rendered ''smaller'' than most images if the user has changed his base width to 300px. In contrast, <code>upright</code> responds gracefully to changes in the user's base width, maintaining the relative size of images in any given article by enlarging or reducing all of them proportionately.

However, a thumbnail can '''not''' be displayed larger than the original uploaded image. For example, if an image is coded <code>thumb|330px</code> or <code>thumb|upright=1.5</code> (for a reader with the usual base width of 220px), but the original uploaded file was only 200px wide, then the article thumbnail will still be displayed at only 200px.