CCSDS 122.0-B-1

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CCSDS 122.0-B-1 is a CCSDS Lossless to Lossy Image compression standard released on November 2005. This CCSDS standard is a discrete wavelet transform (DWT) transform coder followed by a Rice encoder & a Bitplane encoder on the similar lines as Embedded Zerotree Wavelet by Shapiro.

Encoder[edit]

CCSDS 122.0-B-1 is a 3 Level 2D-DWT using a biorthogonal 9/7 (LPF/HPF) tap filters, followed by a bit-plane encoder. It has some design commonalities with ICER and JPEG2000 that use similar wavelet coding schemes.

The encoder can use either floating point or Integer DWT. Integer DWT is the lossless coding scheme, while the floating point DWT contributes to the lossy scheme.

Lesser known features

9/7 INTEGER TRANSFORM

  • An alternative transform in this Recommended Standard is a non-linear approximation to a 9/7 DWT. This extra available non-linear transform can be used to achieve lossless compression.

Known flaws[edit]

In the encoder's current form an image pixel dynamic range of up to 16 bits is supported, whereas ICER and JPEG2000 support 24 and 32 bitplanes.

This compression format is sensitive to bit corruption in the deep space channel, but it is unclear if this sensitivity is greater than ICER or JPEG2000.

The effects of a single bit error can propagate to corrupt reconstructed image data to the end of the affected segment. Measures must be taken to minimize the number of potential bit errors on the transmission link.

There is a known partial fix, but it is not mandatory.

The transport mechanism for the delivery of the encoded bitstream shall support, in the event of a bit error, the ability to relocate the header of the next segment.

In case the encoded bitstream is to be transmitted over a CCSDS space link, several protocols that have built in error correction and detection can be used to transfer the sequence of segments (the highest coding level in this image format).

Lack of updates to the standard are also a problem, as the last revision to the encoder was in November 2005. Unlike ICER that has been used in products and projects outside the space agencies, this image compression system has no history of use outside the space agencies.

References[edit]

  1. Active CCSDS recommendations
  2. CCSDS 122.0-B-1 description
  3. CCSDS