awaforge

Filters — ISO 32000-2 §7.4

AGPL-3.0-onlyRelease 2L4

The /Filter + /DecodeParms chain on streams. Every filter exposes { decode, encode }.

Module PDF filter Abbrev. Spec Deps
pdfFlate FlateDecode Fl §7.4.4 pdfErrors, zlib (@awacloud/fw)
pdfAsciiHex ASCIIHexDecode AHx §7.4.2 pdfErrors
pdfAscii85 ASCII85Decode A85 §7.4.3 pdfErrors
pdfRunLength RunLengthDecode RL §7.4.5 pdfErrors
pdfFilterDispatch orchestrator — §7.4 pdfErrors + the four above

Coverage (decode / encode)

The table below describes the decoders map that pdfFilterDispatch ships out of the box.

Filter decode encode Notes
FlateDecode yes yes /Predictor 1, 2 and 10–15 supported in both directions.
ASCIIHexDecode yes yes Encodes uppercase, wraps every 32 bytes.
ASCII85Decode yes yes Handles z and ~>.
RunLengthDecode yes yes Greedy encoder.
DCTDecode passthrough passthrough The PDF stores the raw JPEG bytes.
JPXDecode passthrough passthrough Raw JPEG 2000.
Crypt passthrough passthrough Real handling lives in the crypto layer.
LZWDecode not registered — An implementation exists on the pdfLegacyDeprecatedFilters extra (lzwDecode/lzwEncode, over @awacloud/fw/io/compress/lzw).
CCITTFaxDecode not registered — Implementations exist on pdfCcittFaxDecoder and on pdfLegacyDeprecatedFilters (ccittFaxDecode).
JBIG2Decode not registered — Header-only support on the pdfJbig2Read extra.

No extra auto-registers itself into the dispatch map: wire the ones you need with dispatch.register(name, impl) — see pdfFilterDispatch.

Fl, AHx, A85, RL, LZW, DCT, JPX and CCF are recognised as abbreviations and expanded to the full filter name before dispatch — so an unregistered LZW raises pdf/filter/unsupported under the name LZWDecode.

Common pattern

const dispatch = runtime.resolve('pdfFilterDispatch');
const decoded = dispatch.decode(streamObj);

See also