The decibels option specifies in decibels how lossy you want each background data chunk to be in relationship with the original document at the specified resolution. The values should increase between 16.0 and 64.0.
For example, --decibels=18.0,25.0,32.0 indicates the following:
Do not use this option with JPEG images, however, as it causes JPEG artifacts to be reproduced.
Supporting commands:
documenttodjvu, phototodjvu