Coding techniques for digital cinema Andreja Samčović University of Belgrade Faculty of Transport and Traffic Engineering

Introduction Film is the best presentation format for cinema content Film is already being replaced by digitally content Archives worldwide - to ingest, store, manage, conserve, access and preserve efficiently film content in digital form Easy and economical access to digital version Digital cinema (DC) intends to meet these requirements Best quality and uncomplicated access to the stored items

Digital Cinema Initiatives In recent years, digital multimedia devices become more and more popular in people’s daily life With the development of digital technology, digital cinema has been putting into practice Digital cinema is a new kind of application for super high definition video To establish an industrial standard for digital cinema, a joint venture of 7 major Hollywood studios, Digital Cinema Initiatives (DCI), founded in March 2002, and put forward specification in 2005

Digital Cinema Initiatives The DCI (Digital Cinema Initiative) specification published in 2005 has selected JPEG2000 instead of H.264 as the video coding standard for digital cinema It shows that JPEG2000 has a better performance in the field of super high definition video coding Until now, only a few basic tests have been done to compare between JPEG2000 and H.264 coding standards Moreover, the test resolutions and characteristics of input sequences are very limited JPEG2000 and H.264 are the latest image and video coding standards, respectively

JPEG 2000 JPEG 2000 standard Material eXchange Format Open Archival Information System (OAIS) reference model - own system architecture Commercial archives - stock-shot licensing companies, newsreel and future collections, producers, and distributors Public film archives - digitally projected cinema, home video and home cinema, internet and television distribution

File formats Two different file formats to store image, audio and metadata Each is able to store archived items in the best possible quality and to facilitate the access to the archived items Set of “modules”, produced at different places and for different purposes To create new metadata modules for different stuff, people and deals

JPEG-2000 coding technique JPEG-2000 Low-complexity standards for lossless image compression do not permit a control of the resulting bit- rate This is possible by using the wavelet based standard JPEG-2000, which allows for an embedded output bit stream that can be truncated at a desired quality level The drawback is increased complexity and a slightly worse performance for mathematically lossless compression JPEG-2000 is based upon a wavelet decomposition of the original image, with up to 5 wavelet decomposition levels

JPEG-2000 coding technique Each subband is divided into rectangular code-blocks, and each code-block is independently coded by an arithmetic codec using progressive bit planes The bit stream is created by using a sophisticated distortion minimization algorithm called EBCOT which gives, for each layer, the optimum contribution of each code block Reversible wavelet transforms were used, and the optional quantization was skipped An intensive simulation campaign showed that no appreciable gain is seen after the second wavelet level, and this level was taken as a reference We finally noted that colour space conversions (RGB, YUV, YCbCr, etc.) do not give any appreciable gain, so that images were compressed directly in their original colour space

Standardization for archival applications The requirements for archival applications: open standard (ISO standard : 2004) allows mathematically lossless as well as visually lossless compression advantage of allowing a scalable presentation of image data compression is performed on an intraframe basis only the use of wavelets and arithmetic entropy coding produces a hierarchical code stream, allowing to encode images at the desired maximum resolution and quality

Standardization for archival applications Figure 2. General encoding structure for JPEG 2000 RATE CONTROL RGB to YC b C r TRANSFORM WAVELET TRANSFORM QUANTI- ZATION ENTROPY CODING PACKETI- ZATION FINAL CODING STREAM

Standardization for archival applications Wavelet-based image compression standard To transform each colour component into a hierarchy of subbands Embedded block coding with optimized truncation (EBCOT) Context-adaptive arithmetic coding to efficiently represent a collection of binary symbols Bit rate and quality are the two primary optimization criteria for rate-control

Simulation results Digital cinema is different in several fundamental ways from other applications The resolution is higher, with a single frame of 4x10 3 data containing approximately 8x10 6 pixels The quality requirements are more stringent Cinema viewers tend to sit within 1,5 to 3 screen heights of the projected image Relative compression efficiency advantages for coding of digital cinema image sequences using JPEG 2000 and H.264 standards

Simulation results The test content used was from the DCI (Digital Cinema Initiatives) minimovie sequence “Confetti Title Screen” Resolution of 4096x1714 (sequence 4K), with 12 bits per colour and 4:4:4 colour sampling To reduce the amount of processing during the experiment, cropped region of size 512x208 (sequence 512) was used a) JPEG 2000; a) JPEG 2000; b) H.264 in which every frame is an I frame; b) H.264 in which every frame is an I frame; c) H.264 with an I frame of period 16, and with both B and P frames used between the I frames c) H.264 with an I frame of period 16, and with both B and P frames used between the I frames

Simulation results Figure 3. PSNR versus bit rate for 4K sequence

Simulation results Figure 4. PSNR versus bit rate for 512 sequence

Conclusion Film is being replaced by digitally content and this lacks film’s noise affordable and more certain future Practical solution - a system ready to be implemented and as an overall approach and model DC archive system is in its implementation phase To meet the needs of archiving and distributing both archival content and current digital productions Digitized analogue film and video, digital video and digital cinema products - to transcode them on demand for distribution