Help:Recommendations for uploading images
Images can be uploaded in various formats. If you are uploading many quality images, the following recommendations may help to choose the best format:
For photographic images, the choice is easy: these are pixel images, and while a completely loss-less format like PNG has some advantages over JPG, a low-compressed JPG (e.g. 98 % quality) is generally very good. Normally you should not convert a JPG to a PNG file—previous quality losses can not be recovered.
When converting images for uploading yourself, provide them in a high to moderately high resolution. Do not downscale them for web-use to 400-800#8239;px: The Wiki will automatically scale images and can do so better with higher resolution images (1500#8239;px or above). When compressing images to JPG, choose a low compression between 90 and 98#8239;% to avoid artefacts. Note that artefacts in JPG images accumulate, i.e. opening and saving a JPG file after modification repeatedly will create very notable quality losses.
For line drawings or graphics, the best images for self-created drawings are vector images. These can be scaled from small to large without loss of quality. Many files like Microsoft or LibreOffice, Adobe Illustrator, Visio, etc. provide such format. Unfortunately, the standardized, web-enabled format for this type of graphic, the SVG Format is poorly supported by Office software. If you can export a vector in SVG format, this is wonderful and the images are directly visible in your wiki pages.
However, we realize that it may often be more practical to use pixel-based formats here as well. If you do so, please avoid using JPG and use PNG or TIFF instead. JPG is optimized for continuously changing colours, and has problems with hard colours like black and white lines. Often a PNG image with loss-less compression is smaller than a JPG for this type of pixel images.
Summary:
A preferred (optimal) upload format for images in order of preferred file formats is suggested to be like:
→ ? ─ already in vector format ─────────────────────────── original file format plus │ (Inkscape, LibreOffice Draw, SVG (Scalable Vector Graphic), PNG │ Visio, Powerpoint, CorelDraw, │ Adobe Illustrator, Freehand, …) └ else │ color? (16 Mio) ├── …or… ──┬ photo? ────────────────── JPG (98%), PNG, TIFF │ gray? (256 colors) ├─ graphic/color fields? ── PNG, TIFF; only exceptionally JPG (98%) │ ├── diagram/line drawing? ─ PNG, TIFF; avoid JPG! │ └─── icon? ──────────────── PNG; avoid JPG! └── BW ────────────────── diagram/line drawing? ─── PNG, TIFF (1 Bit)