Which common image formats are open or royalty-free?
Pearsonartphoto mentioned several raster formats. A couple of other file formats that are used for vector based files:
- SVG (open standard) http://en.wikipedia.org/wiki/Scalable_Vector_Graphics
- PDF (originally proprietary, now open standard) http://en.wikipedia.org/wiki/PDF
A decade later, the raster side of things hasn't changed much. Two more formats have in later years become available, WebP and AVIF, both spinoffs of video intra frame coding, VP8 and AV1 respectively. You may occasionally stumble upon them on the web as they are optimised to produce small file sizes.
These are open and royalty free in the sense that it is believed that all relevant patents have irrevocable grants.
In image archiving, it's not uncommon to use the open and royalty free FFV1 intra-only video format for single image storage, as it has favourable performance at scale.