JpxDecodeFilter Class

Definition

The JPXDecode filter: JPEG 2000 images, from a JP2/JPX file or a raw codestream, decoded in managed code. Decode only.

public sealed class JpxDecodeFilter : IImageFilter, IStreamFilter

Remarks

ISO 32000-2 §7.4.9 and Table 87; ITU-T T.800 | ISO/IEC 15444-1 Annexes A (codestream syntax), B (packets and progression), C (MQ decoder), D (EBCOT tier-1), E (reconstruction), F (inverse wavelet transform), G (DC level shift and component transformation) and I (JP2 boxes). The codestream's width, height and precision win over the image dictionary; with a ColorSpace in the dictionary, the image has that many channels.

All of Part 1: main and tile-part headers (COD, COC, QCD, QCC, RGN, POC, PPM, PPT, with their precedence), any number of tiles, tile-parts (in TPsot order) and layers, any precinct and code-block partition, the five progressions and progression volumes, SOP and EPH markers, packed packet headers, tier-1 with every code-block style, region-of-interest Maxshift, the 5/3 and 9/7 filters with dequantization, the RCT and ICT, the DC level shift and sub-sampled components (replicated over the image grid).

The JP2 wrapper follows ISO 32000-2 §7.4.9: with an Indexed ColorSpace the codestream's indices are the samples; with another ColorSpace its first N colour channels (in channel definition order) are, and the JP2 colour boxes are ignored; without one, the palette and component mapping, the channel definitions and the colour specification of highest precedence decide the channels and the colour model (ColorModel, IccProfile), sYCC, YCbCr and CIELab converted to RGB. With SMaskInData the opacity channel becomes Alpha, premultiplied for SMaskInData 2 or a premultiplied channel definition.

Reduced resolutions (issue #362): asked for a reduction d by Reduction, the image facet decodes resolutions 0 to N_L − d of every tile-component (ITU-T T.800 B.5), skipping tier-1 for the code-blocks of the dropped sub-bands and the inverse DWT of the dropped levels, which gives the image at 1/2^d, as opj_decompress -r d does. The header offers the fewest decomposition levels of any tile-component (MaxReduction), and no more than keep the image origin on the reduced grid. The packets of dropped resolutions are still read in order where the progression interleaves them (PCRL, CPRL, LRCP with several layers, progression order changes); in RLCP, RPCL and LRCP with one layer they are the tile's last and are not read (B.12.1). Only viewers ask for it.

Through Decode(ReadOnlyMemory<Byte>, IBufferWriter<Byte>, FilterContext) the output is the colour samples of DecodeImage(ReadOnlyMemory<Byte>, ImageFilterContext) in the §8.9.3 layout, at the bits per component of the greatest precision (rounded up to 8 or 16 for 3 to 7 and 9 to 15). Lenient repair: a truncated codestream decodes what is present (JpxCodestreamTruncated); strict mode throws instead. Stateless and thread-safe.

Properties (1)

Methods (3)