JPEG 2000 Reliable Video Quality from Production to Archiving Jean-Baptiste Lorent and Jerome Meessen, intoPIX

Today, the broadcast industry is increasingly turning its attention towards JPEG 2000. In recognition, the JPEG committee is currently finalizing the standardization of a new profile specifically dedicated to broadcast applications. This should be of no surprise as already the JPEG 2000 compression format guarantees the highest image and video quality while also offering many other properties that are particularly useful to the industry.

JPEG 2000 momentum in broadcast: why now?

Just a few years after its formal adoption by the digital cinema industry, JPEG 2000 is now being recommended in broadcast through various industry initiatives and standards. And: The JPEG committee is close to announcing the publication of its dedicated broadcast profile. Under the impulse of the Video Service Forum, JPEG 2000 transport over MPEG-2-TS is under standardization. Recently, several product manufacturers together formed the JPEG 2000 Alliance promoting the benefits of this format. Lastly, a wave of archiving initiatives are today favouring JPEG 2000 over other formats – including uncompressed TIFF – for saving their audio-visual heritage for future generations.

There is a good reason behind this momentum; the role of video compression formats has fundamentally changed over recent years. With ever growing transmission and storage capacity, coupled with increasing content quality and quantity, the problem is not the ability to robustly compress the content anymore. Today, the challenge is to manage the quality of the content and the access to it over entire workflows.

Formats offering compression ratios superior to JPEG 2000, such as MPEG-4 AVC/ H.264, still have to cope with the challenging consumer context where mobility, shared networks and wireless will remain key aspects. Today’s professional broadcasters prefer to avoid intrinsic image degradation in order to ensure and maintain a reliable image/ video quality from acquisition and production through to distribution and preservation: just what JPEG 2000 offers.

How does JPEG 2000 work?

Firstly, JPEG 2000 is an intra-frame compression format, i.e. each video frame is compressed independently as a still picture. This provides a quality guarantee, but does create a barrier to strong compression factors. Again, it all depends on the expectation of the format. For example, if the purpose of compression is the distribution of essence and no further editing is expected, long-GOP MPEG should typically be preferred. However, if the purpose is production, I-only compression formats are ideal.

After a pre-processing phase, mainly dealing with colour de-correlation, the video frames are passed through recursive low (L) and high (H) pass wavelet filters (see Figure 1). This process is known as the Discrete Wavelet Transform (DWT). It corresponds to an intra-component de-correlation that restructures the image by concentrating the image information in a small and very localized area. The recursive DWT also leads to a multi-resolution image representation. Next, the data is quantized and encoded in the Entropy Coding Unit. The quantization and the coding together achieve the compression before organizing the code stream according to a rate- distortion optimization.

Figure 1. The wavelet transform: the key step of the JPEG 2000 compression. 18

EMERGING STANDARDS