The mention of "4K" is significant in this context. While the adult industry has largely shifted to digital streaming, the major Japanese studios like S1 have increasingly adopted 4K cameras and mastering processes. This allows for higher bitrates and sharper images, which is a key selling point for physical media (Blu-ray) collectors and digital downloaders.

Furthermore, the original camera negatives for SSIS-903 were reportedly shot on 6K sensors, downsampled to 4K. This means the 4K release contains more detail than the original 1080p release, which was a downscale of the same 6K footage. You are seeing the maximum fidelity the source material can provide.