All flags supported by libjpeg-turbo are present here (descriptions are taken from libjpeg-turbo header). When you need to pass flags to any function in this wrapper use a list containing the following symbols (the order does not matter):

• :bottomup — The uncompressed source/destination image is stored in bottom-up (Windows, OpenGL) order, not top-down (X11) order.
• :fast-upsample — When decompressing an image that was compressed using chrominance subsampling, use the fastest chrominance upsampling algorithm available in the underlying codec. The default is to use smooth upsampling, which creates a smooth transition between neighboring chrominance components in order to reduce upsampling artifacts in the decompressed image.
• :fast-dct — Use the fastest DCT/IDCT algorithm available in the underlying codec. The default if this flag is not specified is implementation-specific. For example, the implementation of TurboJPEG for libjpeg[-turbo] uses the fast algorithm by default when compressing, because this has been shown to have only a very slight effect on accuracy, but it uses the accurate algorithm when decompressing, because this has been shown to have a larger effect.
• :accurate-dct — Use the most accurate DCT/IDCT algorithm available in the underlying codec. The default if this flag is not specified is implementation-specific. For example, the implementation of TurboJPEG for libjpeg[-turbo] uses the fast algorithm by default when compressing, because this has been shown to have only a very slight effect on accuracy, but it uses the accurate algorithm when decompressing, because this has been shown to have a larger effect.
• :stop-on-warning — Immediately discontinue the current compression/decompression/transform operation if the underlying codec throws a warning (non-fatal error). The default behavior is to allow the operation to complete unless a fatal error is encountered.
• :progressive — Use progressive entropy coding in JPEG images generated by the compression and transform functions. Progressive entropy coding will generally improve compression relative to baseline entropy coding (the default), but it will reduce compression and decompression performance considerably.