FORMAT



JPEG 2000

The JPEG 2000 format is used primarily within the DCP (Digital Cinema Package) format.

It is characterised by very high quality image reproduction.

The JPEG 2000 compression technology was developed by the Joint Photographic Experts Group to overcome the challenge of existing JPEG compression techniques reaching their limits as digital images were increasing in resolution and size. This increase in compression needed to produce manageable file sizes was leading to less and less acceptable results.

In contrast to the JPEG standard, which achieves data reduction through a discrete cosine transform  (DCT), JPEG 2000 uses a discrete wavelet transform (DWT).

In simple terms, the main difference is that in a DWT, the image is viewed by the codec as a whole, and is not broken down into a block structure. This means that JPEG 2000 compression is free of the unsightly blocky artifacts and moiré patterns perceived at higher compression ratios in JPEG (and MPEG) codecs.

The JPEG 2000 compression process is mathematically lossless when applying a compression factor of c.2:1 meaning that exact image information is always maintained.  In this scenario, the output quality is maintained even if the encoded images are converted back into a video signal and then re-compressed using the same codec.

JPEG 2000 images remain visually lossless for compression ratios up to 20:1, in spite of the signification data reduction. Where higher levels of  compression of about 50:1 to 100:1 are used, the encoded output becomes lossy. Degradation is, however, mild and still provides an advantage over the results of JPEG or MPEG-compressed images with comparable factors. Visual artifacts appear as a slight blur in image areas of high contrast (high-frequency areas) or near the edges of the image.

Because this encoding method has been on the market since 2000 and is license-free, software support is now widely available.

Existing applications have adapted JPEG 2000 profiles. The following table compares the four typical application profiles.

JPEG2000 Profiles

  • Live Broadcast Contribution: HD, YUV, 4:2:2 or 4:4:4, 10-bit, lossy, <100Mbit/s

  • High Quality Delivery For Broadcast: HD, YUV, 4:2:2 or 4:4:4, 10-bit, nearly lossless, up to 1Gbit/s
  • Digital Cinema: 2K/4K, XYZ, 4:4:4, 10-bit, visually lossless, < 250Mbit/s
  • Digital Cinema Archiving: 2K/4K, XYZ, 4:4:4, 16-bit, mathematically lossless, >1Gb/s