RAW file preview
All RAW files are like containers which include - 1 to1 pixel data generated by camera sensor (without any manipulation) + colour coding info + metadata data + optional previews + data verification info.
- When you convert it to JPEG/PNG or any other format you compress that data into smaller and accessible format.
- DNG RAW was one of the original standardised RAW formats which described how the data will be packaged when camera/scanners generate similar data.
- CR2/CRW (Cannon), NEF (Nikon) etc. are proprietary formats which are built upon original RAW standards.
- Few camera companies still use DNG as RAW format generated by their cameras.