From Just Solve the File Format Problem
Lossless JPEG may refer to:
- The standard lossless modes of the original JPEG format
- The JPEG-LS format (which is fundamentally lossless, but supports a kind of lossy compression)
- A lossless JPEG transformation. A lossless JPEG transformation is not a format; it refers to the process of editing (e.g. rotating or cropping) a lossy JPEG image without causing any additional loss of image quality.
- (Incorrectly:) A high quality lossy JPEG. Many people have the reasonable belief that the highest available quality setting (e.g. "100%") will produce a lossless JPEG, but that is almost never the case. JPEG quality settings are defined by the application, so we can't say for sure, but the highest quality setting is usually still lossy.
Less-likely things it could mean:
- Only the lossless form of JPEG-LS
- The lossless form of JPEG XT
- The nonstandard SmartScale features promoted by the IJG libjpeg software, when used to achieve lossless DCT compression
- The set of all formats that are lossless and have JPEG in their name, which could even include some forms of JPEG 2000 and JPEG XR