RPS Film Imaging

JPEG2000 Compression


Digital Cinema JPEG2000 encoder

Our encoder was designed specifically for the demands of digital cinema and has been refined constantly since it's creation in 2008. Now in it's fourth major revision, it generates the very finest pictures available anywhere using our proprietary variable bit rate encoding scheme.

Variable bit rate (VBR) encoding allows the DCP's picture data rate to vary depending upon the complexity of the picture to be compressed. On the other hand, constant bit rate (CBR) encoding compresses every frame to the same size regardless of it's complexity and how grainy or noisy it is. Thus, the amount of damage the compression does to each frame will vary depending on the source image. The VBR compressed image will always have the amount of compression damage strictly limited (and are thus sometimes called constant quality encoders)

Most mastering facilities naively turn down the bitrate of their CBR encoder to make DCPs of a size suitable for distribution. The CBR encoder then creates images where the encoder damage can (and does) become visible; using our VBR encoder this will never happen, while still keeping the DCP size as small as possible.

The following graph demonstrates this using the industry standard PSNR quality measure, illustrating how a CBR encoder's quality can vary dramatically while our VBR encoder tries to maintain a given quality measure. These are the unmanipulated results from a 60 second commercial – Nova Scotia Tourism, comparing a CBR encoder running at 85Mbit/s against our VBR encoder with the quality set to 45dB PSNR and the maximum bitrate set to 125Mbit/s.

Because our VBR encoder is controlling the bitrate intelligently we achieve a higher average PSNR measure – 45.45db compared to the CBR encoder – 45.28db. Our DCP is also considerably smaller – 710Mbytes compared to the CBR encoder at 1280Mbytes.




 

RPS Film Imaging