Since the JPBD only includes the main episodes, the specials were produced using the USBD.
The source quality is mediocre, suggesting that the production team hardly engaged in sakuga, with simplistic image colors and the application feeling heavy, akin to an oil painting. This cost-effective production method mitigated some common artifacts, such as aliasing and color banding, but also introduced more defects, like evident ringing and DCT noise. The entire film exhibits strong dynamic noise: on the one hand, the excessive dynamic noise acted as a safeguard for the flat areas, rendering the color banding less detectable; on the other hand, after the destruction by the encoder, noise around the lines left noticeable DCT noise. The ringing, likely affected by both post-production sharpening and the encoder's damage, with USBD's encoding parameters being inferior to JPBD's, resulted in more ringing and DCT noise.
In terms of processing, aside from conventional anti-aliasing, de-banding, and compensatory sharpening, we adaptively removed excessive noise, including DCT noise, and then compensated with some dynamic noise to preserve the viewing quality, supported by combined de-ringing to restore the lines.