A callback function that can be used to modify the DCT coefficients after they are losslessly transformed but before they are transcoded to a new JPEG file. This allows for custom filters or other transformations to be applied in the frequency domain.
Arbitrary data that can be accessed within the body of the callback function
One of the @ref TJXOP "transform operations"
The bitwise OR of one of more of the @ref TJXOPT_CROP "transform options"
Cropping region
Lossless transform